Radioactive isotopes for research, medicine, technology

AstroNuclPhysics Nuclear Physics - Astrophysics - Cosmology - Philosophy Physics and nuclear medicine

1. Nuclear and radiation physics
1.0. Physics - fundamental natural science
1.1. Atoms and atomic nuclei
1.2. Radioactivity
1.3. Nuclear reactions
1.4. Radionuclides

1.5. Elementary particles
1.6. Ionizing radiation


1.4. Radionuclides
In this chapter we will approach the origin and properties of the most important radionuclides - important either in terms of physical or general science, or radionuclides used in various fields of science and technology, including medicine, in industrial applications, radionuclides occurring in the environment, etc.   Mendeleev's periodic table contains 118 now known elements. However, there are significantly more radionuclides than stable nuclides, a total of over 2000 are known. Within a single element, several radioisotopes are usually represented , sometimes even ten or more.

Natural radionuclides
In addition to stable chemical elements, radioactive elements of natural origin also occur in very low concentrations in the natural environment . These natural radionuclides can be divided into three categories according to their origin and formation :

To sum up, long- lived radioisotopes with a half-life of more than about 100 million years occur in our terrestrial nature . Of the shorter ones, only those that are continuously created by natural processes - cosmic radiation or in the decay chains of long-term isotopes. All other short-lived radioisotopes, formed during stellar nucleogenesis in large quantities (especially in supernovae) , have not been preserved on Earth - they are sometimes called extinct, defunct, vanihed, extinct radionuclides ; their former existence is evidenced by the observed surplus of stable products of their decay (cf. below " Radiometric dating ", passage " Dating using decayed radionuclides "). Such important extinct radioisotopes are iodine 129 I , aluminum 26 Al, and iron 60 Fe, whose radioactivity may have been involved in the formation of the protoplanetary disk, planets, and asteroids at the beginning of the solar system's development.

Radioactivity in the environment
All nature (terrestrial and space) contains a small amount of radioactivity , especially the above-mentioned natural radioactive elements. Compounds of primary and secondary radionuclides (radioactive decay series) enter the soil , water and air
(especially through gaseous radon) from rocks during their erosion . During the combustion of coal , some natural radionuclides are released into the air (especially radon 222 Rn, polonium 210 Po and lead 210 Pb), which accumulate at greater depths due to the decay of the primary natural radionuclides uranium and thorium. During volcanic activity , the ejected clouds of volcanic smoke and dust contain a significant amount of radon radionuclides, polonium-210, lead-210 from great underground depths. Compounds of cosmogenic radionuclides also enter the biosphere from the atmosphere. From soil, water and air, natural radionuclides get into plants and in the food chain into animals and humans.
  In our environment, therefore, we are constantly exposed to ionizing radiation from cosmic rays and natural radionuclides in the air, in surrounding objects, in soil and rocks, building materials, even in our bodies.


Fig.1.4.2. Scintillation spectrum of gamma radiation of clay
(sample of 200g of arable land from Central Moravia) . Weak gamma peaks from the secondary radionuclides of the uranium and thorium decay series (isotopes of bismuth, thallium, lead) and a relatively significant 1460 kV peak of the primary radionuclide potassium 40-K are evident.

In recent decades, this has been approached by radiation exposure to artificial radiation sources - X-rays, accelerators, artificial radionuclides. Especially in targeted use in medical radiodiagnostics and radiotherapy, and possibly also from unwanted radioactive contamination (radiation accidents, nuclear waste) - 5.2, part " Sources of radiation by ionizing radiation ". The favorable and unfavorable biological effects of that natural and artificial radiation are discussed in detail in 5.2 " Biological effects of ionizing radiation ".

Geological significance of natural radioactivity
Although the relative content of natural radionuclides in the "building" material of the Earth is not high, their total amount in the Earth's interior and crust is so large, that the energy released by them can have considerable geothermal significance .
  
According to current geological knowledge, our planet Earth consists of several layers. The solid surface consists of a relatively thin layer of earth's crust , the so-called lithosphere (Greek lithos = stone ) , about 5-50 km thick (depending on whether we are in the sea, land, mountains). The Earth's crust is not solid, but is "broken" into individual lithospheric plates which move slowly relative to each other. Below it lies the Earth's mantle (further divided into the upper and lower mantle), which is to some extent malleable (plastic) and forms the largest part of the volume and weight of the globe. It consists of partially molten rocks with a temperature of about 600-1250 C. Thermal convection takes place in the mantle , through which heat is transferred from the inner part of the Earth to the surface. The plasticity of the mantle, on which the individual parts (plates, "floes") of the earth 's crust and the convection of heat "float" is the driving force of continental shifts, plate tectonics and volcanic activity *). Inside the Earth is the Earth's core (Moon size) in which the temperature is likely to exceed 4000 C; its outer part is fluid, the inner core at the very center of the Earth is (according to indirect geological measurements) solid. The solid iron inner core of the Earth "floats" and rotates in the liquid outer core, which generates a geomagnetic field. This magnetic field creates a "shield" against ionizing cosmic radiation and the solar "wind". Without him, life on the planet would not be possible.
*) These are "ordinary" volcanoes located in places where lithospheric plates collide. However, beneath the thin shell of the earth's crust, in the earth's mantle, like a "time bomb", massive streams of hot molten rocks rise by thermal convection . If it melts to the surface, under great pressure they erupt as destructive supervolcanoes .
  Total
heat flux from the Earth's interior is estimated at about 45 Terawatts *). Such a massive heat flux is difficult to explain by the heat remaining inside the Earth (due to the long time of about 4.5 billion years since the Earth's origin) , or tidal gravitational action during the Earth's rotation, the Moon's orbit around the Earth and the Earth around the Sun (1.2, passage " Gravitational gradients - tidal forces " in the book "Gravity, black holes ...") . The radioactive decay of natural radionuclides could contribute about 60% to the development of heat in the Earth's interior . After 8-10 TW, the decay series of 232Th and 238 + 235U isotopes could supply , 40 K of radioactive potassium would contribute 3-5 TW of heat flux.
*) The average density of geothermal heat flux at the Earth's surface is about 65-100 mW / m2 , which is less than ten thousandths of the intensity of incident solar radiation.
  It has also been hypothesized that a natural fission nuclear reactor similar to the one found in the Oklo mine could operate inside the Earth
(see 1.3, section " Nuclear reactors ", section " Natural nuclear reactors? ") . Billions of years ago, when the concentration of fissile uranium 235 U was still high enough, this is quite likely. In order for such a reactor to function even at the present time, when the share of fissile 235U considerably decreased, the concentration of uranium in the material inside the Earth would have to be significantly higher than in the rocks we know of the earth's crust; about it we have no evidences.
  We have relatively little information obtained indirectly about the structure of areas inaccessible to us. Important data on the distribution of radioactive elements in the Earth's interior could be obtained by detecting neutrinos , so-called geoneutrinos , formed during
b- radioactive decay of natural radionuclides, which freely pass from the Earth's interior through thick rock layers to the surface (see 1.2, section " Neutrinos - "ghosts" between particles ", passage" Neutrinos from natural radioactivity ") .

Radioisotope (radiometric) dating
The independence of the rate (half-life) of radioactive decay from external conditions *) allows the use of the exponential decay law of radioactivity as a kind of clock - a natural "chronometer".
*) Situations where the course and rate of radioactive decay may depend somewhat on external radiation or chemical factors are discussed in 1.2, section " Independence of radioactive decay on external conditions ".
  The basic idea of using radioactive decay to measure time is simple. If we know the initial number N
0 (at time t = 0) of radioactive nuclei of the parent nuclide X with a known half-life T1/2 in the sample, then by measuring the absolute activity A(t) of the sample, or the ratio of the concentration of parent X and daughter Y isotopes, at some later time t we can determine from the decay law this time t , elapsed from the sample (t = 0) to the time of measurement - thus the age of the sample . From the decay law of radioactivity (derived in 1.2, part " General laws of transformation of atomic nuclei ") N X (t) = N X (0) .e -l .t = N X (0) .e - t. (Ln2 / T 1/2 ) = N X (0) .2 - t / T1/2 ; N Y (t) = N X (0). [1 - e -l .t ] = N X (0). [1 - e - t. (Ln2 / T 1/2 ) ] = N X (0) [1 - 2 - t / T 1/2 ], for the sought age t the formula follows
         t = T
1/2 . [1 + N X (t) / N Y (t)] ,
where N
X (t) is the current amount of the parent element X and NY (t) is the current amount of the daughter element Y in the test sample (the initial amount of N X (0) of the parent radionuclide is usually unknown, sometimes we try to estimate it, eg at 14C) .
  All materials (on Earth and in space) contain a small amount of natural radionuclides with long half-lives. The rates of their radioactive transformation can, under certain conditions, be used to determine the ages of various objects and samples of materials. This method of determining the age of samples is generally called radioactive, radioisotope or radiometric dating , or radioisotope chronometry ; according to the investigated nuclides then eg radiocarbon dating
(using carbon-14, described below), potassium-argon or uranium-lead dating. It is used in archeology, paleontology, geology ( geochronology ) and astronomy (age of meteorites and planets).
  There are two basic conditions that should be met for accurate radioisotope dating :
1. The initial conditions are known - the concentrations or ratios of the parent and daughter isotopes at the time of the natural origin of the investigated material (at time "0");
2. The investigated materials must be closed or isolated systems from their inception , so that no parent or daughter isotopes have escaped or entered them.
  These conditions are never 100% met, so "straightforward" radiometric dating is not completely accurate. It will be outlined below which methods can be used to perform independent calibrations and increase the accuracy and reliability of radioisotope dating
(so-called isochronous and cocondon dating is described ) .
Radiocarbon dating method (also called carbon chronometry )
using radiocarbon
14C to produce the effect of neutrons ejected cosmic rays from nuclei of atoms on the nitrogen in the higher-layer earth's atmosphere n a + 14 N 7 14C6+ p + (see 1.6, section " Cosmic radiation ", Fig.1.6.7) . This creates about 2 atoms of 14C per second per 1 cm3 of atmosphere. Carbon 14 C, as a long-term radionuclide (T1/2 = 5730 years, pure b - , energy 158keV) constantly contaminates the biosphere , oxidizes to 14CO 2 in the atmosphere , enters the biocycle - the food chain of living organisms on Earth. Through photosynthesis, it gets from the atmosphere into plants, from there through food into the bodies of animals. It is therefore contained in all living organisms. The concentration of 1 atom of 14 C is stabilized to about 8.10 13 atoms of ordinary 12C; one gram of natural carbon in all living organisms contains an activity of about 0.25 Bq 14C. After the organism dies, its metabolic contact with the atmosphere and the supply of 14C are interrupted, so that the concentration of radium carbon begins to decrease by its radioactive b -decay 14 C 14 N + e - + n with a half-life of 5730 years . This also changes the relative proportion between the carbon isotopes 14 C, 13 C and 12 C.
  From the ratio between the relative proportion of radioactive isotope
14C and stable isotopes of carbon in the studied historical object of biological origin (eg wood, remains of organisms, etc.) we can approximately determine the age of this object - the time that has elapsed since the death of the organisms from which the object originated. This method was first used by W.F.Libby in 1946.
  In the simplest case, we measure the specific activity of 14 C in the investigated historical object of biological origin and compare it with the equilibrium specific activity of radiocarbon in the atmosphere and in living organisms. Sensitivity of 14 C activity measurements using proportional or scintillation detectors with liquid scintillators (see 2.6, section " Liquid scintillators"), due to the half - life of 14 C 5730 years, limits the time range of this method to about 30 000 years. Substantially lower values of 14 C / 12 C can be determined by mass spectrometry (see 2.6 , section" Magnetic spectrometers "). The precondition for the correctness of radiocarbon chronometry is that the ratio of 14 C / C12 in the past, was always the same during the period from which the measured samples originated. In order for this ratio to remain constant, the intensity and composition of cosmic rays and their effects on the upper atmosphere must remain constant. The primary cosmic rays coming from interstellar space are likely to be constant for at least 10 5 years. However, the component coming from the Sun is time-varying depending on solar activity (occurrence of sunspots). The effect of cosmic rays on the upper atmosphere depends on how strong the shielding from the Earth's magnetic field is. The intensity of the geomagnetic field fluctuates by about 50% in time periods of about 10 4 years. Another problem is the anthropogenic influence (human civilization activity) on the distribution of radionuclides in the atmosphere. It is both the burning of fossil fuels that affect the CO 2 content in the atmosphere, and the carbon dioxide released into the atmosphere by nuclear tests, especially in the 50s. Determining the concentration of radiocarbon is also of considerable ecological importance . For accurate radiocarbon chronometry, all these influences are distorting, it is necessary to take a correction, compile a calibration curve by comparison with other independent methods (eg with dendrochronology - dating using annual rings in the wood of old trees) .
Luminescent dating - optical and thermoluminescent , 
is based on the "deposition" of electrons released during long - term irradiation of materials with natural radiation in metastable levels and their subsequent release by heating or light irradiation of the sample (see 2.2, passage " Thermoluminescence and photoluminescence dosimetry ", paragraph " Luminescent archaeological dating ").
Long-time minerals dating
Radiocarbon method is not applicable for dating inorganic materials such as rocks y, and also for very long periods of time over millions or billions of years . Here, under certain circumstances, the decays of other long-term natural ones can be used radioactive isotopes, such as the decay of potassium 40K to argon , the decay of the radioactive isotope rubidium 87 to strontium, or the decay of uranium and thorium to the final element of the decay series - lead. Radioactive dating by determining the relative proportion of daughter radiogenic decay products with respect to the parent nuclides makes it possible in geology to determine the absolute age of rocks *), the duration of individual geological epochs, the age of meteorites, the Earth, the Moon and the solar system. However, the accuracy of these methods is, in addition to the technical difficulties of determining small amounts of nuclides, limited by the variety of samples found and their previous destinies.
*) Age of rocks
Under the age of mineralsin mineralogy and geology, the time interval from the time of mineral formation by solidification and crystallization from molten matter to the present (measurement times) is understood . It is assumed that during solidification, the material composition of the mineral is closed ("preserved"), which then does not change otherwise than radioactive transformation.
Note: Due to the small concentrations of the investigated radionuclides and their long half-lives, a simple method of measuring the radioactivity of samples cannot be used. Determination of the concentration of analyzed nuclides is performed by mass spectrometry (see 2.6 , section " Magnetic spectrometers ") .
Potassium - argon method for determining the age of minerals
The K-Ar dating methodin nuclear geochronology uses the decay of natural (primordial) radioactive potassium 40 K with a half-life of 1.26 billion years to stable argon 40 Ar. Natural potassium consists of three isotopes: 39 K (93.258% - stable), 40 K (0.0117% - radioactive) and 41 K (6.73% - stable). The radioactive isotope 40 K decays with a half-life of 1,28.10 9 years in two ways: b -  (89.1%) 40 K 40 Ca + e - + n for calcium; b +  (10.9%) 40 K 40 Ar + e + + n to argon . In a mineral containing potassium from the moment of its formation in crystalline form (and closure), the radioactive isotope of potassium 40 K decreases and a stable isotope of argon 40 Ar, resulting from the conversion of 40 K, accumulates . The age of the mineral can be determined by measuring the content of both isotopes. The 40 K content is determined by measuring the potassium content of the mineral and the known proportion of the isotope 40 K in the potassium. To determine the content 40 Ar, the sample is heated in vacum to a temperature of about 2000 C, whereby argon gas is released from the crystal lattice and the 40 Ar content is determined by mass spectrometry.
  A complementary and refining method of the K-Ar dating method is the argon-argon ( 40Ar /39Ar ) dating method . The mineral sample is first irradiated with neutrons in a nuclear reactor, whereby a reaction of 39 K (n, p) 39Ar takes place on the nuclei of a stable isotope of potassium 39 K. The irradiated sample is then heated in vacum to release both argon isotopes and their content is determined by mass spectrometry. The age of the mineral is determined from the ratio of the contents of the two isotopes of argon (since the amount of 39Ar formed by the reaction with neutrons is proportional to the potassium content of the mineral).
Rubidium-strontium dating
is based on the beta - -radioactive conversion of the natural primordial isotope rubidium-87 : 87 Rb 87 Sr + e - + n to strontium-87 with a half-life of 4,8.10 10 years. If the mineral contains at least a small amount of rubidium, this very slow radioactive transformation causes the content of natural rubidium 87 Rb to decrease and the content of radiogenic strontium 87 Sr to increase since the mineral was formed by crystallization from molten rock . The age of the mineral can be determined from the measured ratio of both isotopes. A complication, however, is that minerals may contain certain amounts of natural strontium and thus of the 87 Sr isotope of non-radiogenic origin *). Therefore, in order to accurately determine the age of the analyzed mineral, it is necessary to correct the determined content of 87Sr to the content of non-radiogenic 87Sr. The determination of another isotope strontium - 86Sr is used for this (again by mass spectrometry). On the basis of the known ratio of 87Sr / 86Sr isotope in natural non-radiogennic strontium (in minerals containing no rubidium), can then be from determined whole content of 87Sr, to subtract the content of non-radiogenic 87Sr.
*) The nuclei of the 87 Sr isotope of non-radiogenic origin were formed together with other strontium isotopes during the nuclear synthesis of elements in space (in supernovae), not by radioactive transformations of 87 Rb.
Dating of rocks by decay of uranium and thorium to lead
This method U-Pb, Th-Pb is based on measuring the current amount of the parent element X (uranium 235 U, 238U or thorium 232 Th) and the end daughter element Y of the respective decay series (lead 207 Pb, 206 Pb or 208 Pb) - see above " Natural decay series ", Fig.1.4.1. From the decay law of the relevant parent element X with a half-life T1/2 , we then obtain for the resulting age t the relation:
             t = T1/2 . [1 + N X (t) / N Y (t)] ,
where N X (t) is the current amount of the parent element X and N Y (t) is the current amount of the daughter element Y (of the relevant lead isotope).
A suitable mineral that serves as a "carrier" for uranium or thorium is zirconium silicate ZrSiO4 , which is commonly found in rocks of volcanic origin. During the formation of a zirconium crystal, uranium or thorium, but not lead, easily enters its crystal lattice. Therefore, when dating, we can assume that all the lead in the sample is of radiogenic origin - it was formed by the decay of uranium or thorium. .............
..... concordant dating - below ...........
Dating using decayed radionuclides
The above methods of radiometric dating require that a certain amount of a small but measurable portion of the initial parent radionuclide. This can be a problem with the oldest samples originating, for example, from the beginnings of the formation of our solar system. In such a case, paradoxically, dating with radioisotopes with a shorter half-life that have already decayed ("died out") and are not present in the sample may help . However, their breakdown products , stable daughter nuclides , are present in the sample . By measuring the concentration of these extinct radionuclide daughter products by mass spectrometry, the relative age of the analyzed sample can then be determined. In co-production with the isochronous technique, it is possible to calibrate, for example, the U-Pb method and specify the determination of absolute age.
  This category includes 129I - 129Xe iodine-xenon chronometry. When the supernova explosion occurs, among others, as well as large amounts of radioactive iodine 129 I is created. The radionuclide iodine 129 I with a half-life of 15.7 million years (which is the current view seems long, but the astronomical point of view is quite short ...) converts beta - -radioactivity to the stable xenon isotope 129Xe . In xenon isolated from stone meteorites of chondrites , a higher content of the isotope xenon 129 Xe was found than corresponds to its usual representation in natural xenon . Surplus 129Xe in chondrites created by radioactive decay of the isotope 129 I ( radiogenic 129 Xe), which was chondrite material enclosed in the formation of a solid silicate composition after cooling the hot gaseous nebula of supernova. In the protoplanetary stage of our solar system, this occurred in the period between about 4.8-4.5. 10 9 years, before the formation of our planetary system.
  In practical use, iodine-xenon chronometry is a relatively complex isochronous laboratory method. The samples are irradiated with neutrons in a nuclear reactor, whereby the stable iodine 127I isotope is converted to radioactive 128 I by neutron capture and the subsequent beta conversion to stable xenon 128Xe. After irradiation, the sample is heated and the released xenon is analyzed in a mass spectrometer, comparing the content of 129- and 129-xenon. ......
Determining the time of formation of meteorites
Meteorites, especially some stone types called chondrites , are among the oldest bodies in our solar system. They were formed when the protoplanetary disk cooled, before the formation of planets (.....). ... link ..... Isochronous dating method
Simple dating methods can be adversely affected by ignorance and variability of initial conditions (different concentrations of parent and daughter nuclides) and the possibility of migration of relevant nuclides between the analyzed material and the environment. To eliminate these effects and refine long-term radioisotope dating, the so-called isochronous method was developed . This more complex (but very elegant) method uses the collection of mineral samples from two or better several different parts (components) of the analyzed rock and performs isotope analysis using three isotopes : not only the parent and daughter element, but also the content of another isotope of the daughter element.
  Thus, we have in the analyzed material the starting parent radioactive nuclide X , which decays with a time T1/2 to a stable daughter radiogenic nuclide Y; the relevant daughter element has yet another stable Y isotope (of non-radiogenic origin). Because all isotopes of a daughter elementY have the same chemical properties, the ratio of these isotopes N Y / N Y in the whole analyzed rock is the same. In contrast, the X isotope has different chemical properties and the initial N X / (N Y + N Y ) ratio is different for different minerals at the time of rock formation. Due to the decay of the radioactive isotope X , the relative proportions of N X / N Y and N Y / N Y in different rock minerals will be different after a sufficiently long time .
  The amount of nuclide Y in the analyzed material consists of the original initial amount N Y(0) and the nuclei formed by the radioactive decay of the radionuclide X . From the law of exponential decay of the parent radionuclide X implies the growth period the concentration of the daughter nuclide a stable radoiogennho Y' relationship N Y' (t) = N Y' (0) + N X (t). [e l . t - 1] . Dividing this relationship by the amount N Y of another stable isotope Y we get the equation for the nuclide concentration ratios:
             [N Y / N Y ] (t) = [ N Y / NY ] (0) + [N X / N Y ] (t) . [e l . t - 1] .
If we choose the time t as a parameter, it is in the ratios of nuclide concentrations the linear equation y = a.x + b, whose graph is a line called an isochron (Greek isos = the same, chronos = time - isochron is a line connecting on the graph of a place with the same time occurrence of the displayed phenomenon) . The slope of this line tg a a = e l . t - 1determines the time t (age), the intersection point (intercept) with a vertical axis b = [ N Y' / N Y ] (0) specifies otherwise unknown initial ratio nuclides Y' and Y .
  Therefore, we measure the current content of N X (t), N Y (t), N Y (t) of these three isotopes in several samples and plot the ratio N X / N Y on the horizontal axis and the ratio N Y / N Y on vertical axis (Fig.1.4.3 left). Using the least squares method, we interpolate the linear regression function - representing the line isochron . If the dependence N Y / N Y is a linearly increasing function of N X / N Y (individual points "fit" well on a straight line), this indicates a good correlation between the measured loss of radioisotope X and the measured increase of the daughter isotope Y. The regression line has the form y = a.x + b, where b represents the original ratio of the elements N Y (0) / N Y (0). The resulting age t is then determined from the relation:
             t = (ln2 / T1/2 ) . [N Y (t) / N Y (t) - N Y (0) / N Y (0)] / [N X (t) / N Y (t)] ,
where T1/2 is the half-life of the initial parent nuclide X . The initial ratio N Y (0) / N Y (0) is found from the regression line.

Fig.1.4.3. Isochronous and concordant analysis in long-term radiometric dating.
Left: Linear regression function - isochron for Rb / Sr dating - interpolated points [ N X / N Y , N Y / N Y ] from several samples of the same rock. Right: Concordia curve for 235 U + 238 U dating, together with discordia (error line) fited with measured values of samples of the same rock.

  The great advantage of the isochronous method is its independence from the original isotope ratio of the daughter element: this unknown original ratio is obtained from the regression line. The original ratio of Y and Y isotopes may have been very different in the past, and yet we get the same age . If the points in the isochron graph do not lie on a straight line, this indicates some events that have disrupted a closed rock system throughout history . The resulting value of age will then not be accurate , and from the regression analysis we can determine the mean square error of the obtained average value.
  The most commonly used triplets of isotopes for the isochronous dating method are listed in Table ( X- the parent parent radoionuclide, Y - its stable daughter nuclide, Y - another stable isotope of this daughter element) :

X T 1/2 [years] Decay of radionuclide X Y Y Y
87 Rb 4,72.10 9 b - : 87 Rb 87 Sr + e - + n        87 Sr 86 Sr
147 Sm 1,06.10 11 a : 147 Sm 143 Nd + a            143 Nd 144 Nd
176 Lu 3.8.10 10 b - : 176 Lu 176 Hf + e - + n     176 Hf 177 Hf
187 Re 4.3.10 10 b - : 187 Re 187 Os + e - + n     187 Pers 186 Pers
235 U 7,04.10 8 a, b - : 235 U 7 a + 4 b + 207 Pb  207 Pb 204 Pb
238 U 4,5.10 9 a, b - : 238 U 8 a + 6 b + 206 Pb  206 Pb 204 Pb

As mentioned above, the reliability and accuracy of long-term dating techniques is, in addition to technical difficulties, limited by the variety of samples found and, in particular, by ignorance of their previous destinies over millions or even billions of years in their history. In exact archaeological, paleontological and geological dating, therefore, great emphasis is placed on the agreement of the results obtained by various independent methods - we are talking about the so-called concordant dating (lat. Concordantiae = agreement, consent, conformity ) .
Concordant radioisotope dating
In radioisotope dating, compliance can be analyzed using two different radionuclides , mainly uranium
235 U and 238 U. It is used here that two radioactive clocks imaginarily, "ticking" inside the sample: the faster "ticking" uranium-235 transforms with a half-life of 700 million years, the slower clock is based on uranium-238 with a half-life of about 4.5 billion flight. Comparing the results from both of these chronometers makes it possible to refine the determination of the age of the sample.
  Two isochronous equations follow from the decay laws for both uranium :
          [ 206 Pb / 204 Pb ] (t) = [ 206 Pb / 204 Pb ] (0) + [ 238 U / 204 Pb ] (t) . [e l238U . t - 1] ,
          [ 207 Pb / 204 Pb ] (t) = [ 207 Pb / 204 Pb ] (0) + [ 235 U / 204 Pb ] (t) . [e l 235U . t - 1] .
If from several measured samples of the same rock we get using these equations two identical independent values of age t - there was a concordance (consent), it is a significant indication of accuracy of the dating method.
  From these two isochronous equations we can also create a so-called concordance diagram (Fig.1.4.3 on the right). Plot the ratio 207 Pb / 235 U on the horizontal axis (on a linear scale) and the ratio 206 Pb / 238U *) on the vertical axis . We use the time t as a parameter: for different values of t we graphically plot the points { [ 207 Pb / 235 U ] (t) ; [ 206 Pb / 238 U ] (t) } . This creates a theoretical curve called a concordia, each point of which gives a concordant value of age t and the ratio of the concentrations of lead and uranium isotopes, provided that no nuclides have entered or escaped from the sample. The values of specific samples from the analyzed mineral are then plotted in this graph. We get points that do not generally lie in the concordia, because the assumption of closure may not be met. Since all isotopes of uranium and isotopes of lead have the same chemical properties, their the leakage from the material is the same and the measured values of the uranium to lead ratio should lie on a straight line. Therefore, we intersect a straight line with the measured points - called discordia (Latin inconsistency, non- contention , discrepancy ) , whose intersections with the concordia represent the initial time t0 crystallization of the material ("maximum age") and time t ("minimum age") corresponding to a possible metamorphosis event during the history of the sample. The concordant diagram serves as an internal check of the dating method, allowing to detect events that violated the conditions of correct dating.
*) These are 207 Pb and 206 Pb radiogenic lead : the initiation of 207 Pb (0) and 206 Pb (0) is subtracted from the total measured amount of these isotopes using the isochronous method .
Determination of the age of the Earth and the Solar system 
Radiometric dating with the help of radionuclides with a very long half-life has been significantly applied not only to geological minerals, but also to determine the age of our planet Earth and the entire solar system. Using only geological methods, determining the age of the Earth is problematic, inaccurate, basically impossible. Due to geological processes - weathering, plate tectonics, volcanism, hydrothermal processes - the chemical and physical composition of the rocks changed significantly.
  In the first half of the 20th century. was the main pioneer of radiometric dating of rocks, geochronology, A.Holmes, who with the gradual refinement of uranium-lead methods determined the age of rocks in the range of about 1.5-3 billion years. His successor, C.C.Patterson, also used the uranium-lead method on the age of meteorites from the early periods after the formation of our planet. Meteorites as cosmic bodies are more advantageous for dating because they have not been altered by any geological processes. In 1965, Patterson measured samples from meteorites found near the Barringer impact crater in Arizona and reached an age value of 4.55 billion years. These measurements were repeated many times, averaging 4.56 billion years
( 1% deviation).
  So this is the value of the age of the planet Earth and at the same time the whole Solar system. All the material in the solar system was formed at about the same time, the various chemicals, including radioactive isotopes, formed together. This is shown by measurements of different meteorites from different regions of the Solar system - individual planets formed at virtually the same time
(from an astronomical point of view).
  On the formation of stars and planets and their chemical evolution, see 4.1, part "
Evolution of stars", on primordial cosmological nucleosystesis 5.4, part "Lepton era. Initial nucleosynthesis" in monograph "Gravity, black holes and space-time physics". For determining the ages of various objects in the universe (stars, galaxies, the entire universe), see 4.1, passage "Ages of objects in the universe".

Production of artificial radionuclides
For the needs of current science and technology, industry and healthcare, we are far from sufficient with a few radionuclides of natural origin
(natural radionuclides uranium 235 and 238 are, however, the basis of fission nuclear reactors and nuclear energy based on them) . So we have to make radionuclides artificially .


Fig.1.4.4. By bombarding the target nucleus A with an accelerated elementary particles, the nuclear reaction produces the resulting core B .
The resulting nucleus B is initially formed usually in the excited state B', followed by deexcitation of gamma photon emissions. This is usually not important for the production of radionuclides, except in situations where the excited nucleus is metastable with a longer half-life.

In order to produce a radioactive nucleus from a stable nucleus, it is necessary to change the number of protons or neutrons so that the equilibrium configuration is disturbed. As discussed in the previous 1.3 "Nuclear reactions", we achieve this according to Fig.1.4.4 by bombarding initial target nucleus A suitable particles - protons or neutrons (or alpha-particles, deuterons, occasionally heavier ions) that enter into the nucleus and bring about appropriate changes there - nuclear reactions ; the resulting nucleus B is formed (mostly in the excited state B , after the gamma radiation then in the ground state) , which is often radioactive .
Production equation and yield 
Thus, if we irradiate a target containing N atoms of the initial irradiated element (nuclei
A ) with a beam of particles (protons or other charged particles from a cyclotron, or neutrons from a nuclear reactor) with intensity I [number of particles / cm2 / sec.], the atoms of the resulting radionuclide ( B ) will gradually accumulate in the target . During the irradiation time t , the activity A(t) of the desired radionuclide in the target will be approximately given by the production equation
                         A (t) = I. N.
s . (1 - e -l .t ) ,
where
s [cm2] is the effective cross section of a given nuclear reaction and l [s -1 ] is the decay constant of the emerging radionuclide (related to the half-life by the relation l = 0.693 / T1/2 ). The amount of activity produced is thus directly proportional to the intensity of the irradiating beam I, the amount of target substance and the effective cross section of the reaction *). Initially, this amount is approximately proportional also to the irradiation time t , but the effect resulting from radioactive decay of the radionuclide, expressed saturation factor (1 - e -l T), the increase in the number of generated nuclei gradually slows down and after about 5-6 half-lives of the resultant radionuclide B, the saturation state (approx. 98%) is already achieved , the rate of production and disintegration is balanced, the activity no longer increases during further irradiation. The resulting activity of the produced radionuclide B is then A = I.N.s .
*) These regularities apply under simplified assumptions of a homogeneous and time-constant beam of radiation and a thin target containing many times more starting atoms (
A ) than the number of emerging nuclei ( B ).


Dependence of the effective cross section of nuclear reactions on the energy of bombarding with neutrons (left) and protons (right).

The effective cross section of a nuclear reaction, and thus the yield of production, depends significantly on the energy of the irradiating particles. This dependence is generally complex and diverse for different types of production reactions.
  When irradiated with neutrons , the effective cross section for slow neutrons is usually higher
(although some reactions take place on the contrary with higher energy neutrons) . With increasing energy, the efficiency decreases monotonically, as faster neutrons remain in the field of nuclear forces for a shorter time, thus reducing the likelihood of a nuclear reaction. In the region of tens and hundreds of eV, the energy dependence appears to be a complex structure of resonant maxima and minima (caused by discrete levels of nucleon energies in the nuclei) .  
  Irradiation with protons (as well as deuterons or heavier positive particles) leads to nuclear reactions only when a certain threshold energy required to overcome the repulsive electrical (Coulomb) barrier around the nucleus *) is reached , with the cooperation of the tunneling phenomenon. Therefore, the effective cross section initially increases significantly with energy, reaches a maximum and then decreases monotonically
(because energy protons quickly pass through the region of the nucleus and in this short time the nuclear reaction is less likely to take place) . For the simplest reaction (p, n) in medium-heavy nuclei, the threshold energy of protons is about 5 MeV and a maximum yield of aboud 10 MeV. For more complex reactions, with alpha-particles and heavier nuclei, the yield curve is shifted to higher energies, 20MeV and higher.
*) Under this energy, a proton can penetrate the nucleus only through a quantum tunneling phenomenon (1.1, passage " Quantum tunneling phenomenon "), with a much lower probability.
  These laws of energy dependence apply not only to the required production reactions, but also to possibly other parallel "parasitic" reactions running in the target material, in which radionuclides other than the required ones are formed - radionuclide impurities . It is therefore necessary to set a certain optimal energy , guaranteeing a high production yield with a minimum content of radionuclide impurities.


Fig.1.4.5. Production of radioisotopes by irradiation of target nuclei in a nuclear reactor (left), a neutron generator (middle) and a cyclotron (right).

Production of radionuclides in a nuclear reactor
The easiest way is to irradiate the nuclei with neutrons - since the neutron does not have an electric charge, it does not cause electric repulsive forces and even a slow neutron willingly enters the nucleus. The most common reaction here is simple neutron capture (n,
g ) : N A Z + n o N + 1 B Z + g *) , but reactions of type (n, p), (n, a ) can also occur . Irradiation with neutrons generally produces nuclei with an excess of neutrons, which usually show radioactivity b- . The nuclear reactor is an intense source of neutrons (1.3, part " Nuclear reactors ") , so that these b- radionuclides are produced by irradiating a suitable target material in the irradiation chamber of the reactor - Fig.1.4.5 on the left. Some reactions of radionuclide production by neutron irradiation are, for example: 6Li(n,a)3H, 14N(n,p)14C, 32S(n,p)32P, 98Mo(n,g)99Mo, .... Specific methods for producing a number of important radioisotopes are described below in the section " Properties of some of the most important radioactive isotopes ".
*) Note: Neutron capture during the formation of radioactive nuclei is also used in a very sensitive method of chemical composition analysis - neutron activation analysis . Irradiation of the examined sample with neutrons results in the formation of radionuclides ("activation"), after which therelevant radionuclide and the corresponding (inactive) starting nuclide can be determined byspectrometric analysis of the emitted radiation energies (especially g) of the activated sample, using calibration also its content in the investigated material. The method is described in more detail in Chapter 3 "Application of ionizing radiation", 3.4, section " Neutron activation analysis ".
  Another frequently used method for the production of radionuclides in a nuclear reactor is the irradiation of uranium with 235 U neutrons, which causes the fission of uranium nuclei into smaller nuclei that are radioactive, eg :
235U + n 236U 131I + 102Y + 3n
                        
137Cs + 97Y + 2n
                        
133Xe + 101Sr + 2n
                        
99Mo + 135Sn + 2n
                        
155Sm + 78Zn + 3n
            ......... and other radionuclides.
  From these fission products , the required radionuclides (e.g.
131 I, 99 Mo, 133 Xe and others) are then isolated by radiochemical methods. Since the heavy nuclei of uranium have a significantly higher percentage of neutrons than the medium - heavy nuclei formed by their fission, these radionuclides have an excess of neutrons and show radioactivity b - .
  A less commonly used method for the production of radionuclides is their chemical separation from fission products of uranium as fuel in the reactor. In a nuclear reactor, 235U (or 238U) uranium nuclei split after the entry of neutrons into two nuclei, chemically falling into the middle part of Mendeleev's periodic table, which are mostly radioactive . The most common nuclei formed in this way are, for example, 131 I, 137 Cs, 90 Sr, .... Spent fuel cells from the reactor contain a large amount of these radionuclides (of the order of TBq). However, it is very difficult to radiochemically isolate individual radionuclides from this diverse mixture so that the radionuclide obtained does not contain traces of other radionuclides - in order to have a satisfactory radionuclide purity, was not contaminated.
Accelerator-controlled neutron generator
In addition to nuclear reactors, accelerators can also be intense sources of neutrons. Protons accelerated to high energies are allowed to strike a (primary) heavy metal target (lead, bismuth, tungsten), where they cause fragmentation reactions in which a number of particles and fragments, especially large numbers of neutrons , are ejected from the target nuclei . The neutrons slow down in the moderator
(it can be water, which also cools the target) and hit the production targets , located around the place of neutron formation, in which the nuclear reactions produce the desired radioisotopes - Fig.1.4.5 in the middle.
  This method is still rather experimental, but it seems relatively promising . In addition to the production of radionuclides, it also enables the disposal and reprocessing of radioactive waste with long-term radioisotopes and the extraction of nuclear energy from thorium - it is discussed in more detail in 1.3, section " Nuclear reactors ", section "
Accelerator-controlled transmutation technology ADTT ".

Production of radionuclides in the accelerator
For the production of positron
b+ -radionuclides, on the contrary, it is necessary to add protons to the nucleus. In order for the p+ proton to enter the nucleus, it must be accelerated to a high energy of the order of hundreds of keV to several MeV in order to overcome the repulsive electrical Coulomb force of a positively charged nucleus with its kinetic energy. The most common proton accelerators are cyclotrons ( 1.5, passage " Cyclotron ") , which accelerate protons by electromagnetic forces during many orbits in a circular path (maintained by a magnetic field) to high energies. The proton beam is then led out from the circular path by the magnetic field and impinges on a suitable target material - Fig.1.4.5 on the right. Depending on the energy of the protons, a number of reactions can take place. The simplest of these is the radiation capture of a proton (p, g ): N A Z + p + N + 1 B Z + 1 + g , but reactions of the type (p, p), (p, n), (p, d), (p, a ) also occur, especially at higher energies and in heavier nuclei.
  For the purpose of the nuclear reaction and transmutation, in addition to protons, the nuclei can be irradiated with other fast charged particles: deuterons d - take place mainly reactions (d, n), (d, p),
a-particles - reactions ( a , p), ( a , n) *) occur , or even heavier nuclei or ions .
*) Note: Nuclear reactions ( a , n) are also used as neutron sources . For this purpose need not have a helium nucleus artificially accelerated, but suffice with suitable a -radionuklides which we mix homogeneously with a suitable target material - some light elements, which give a high yield of neutrons in reaction ( a , n). The most suitable is beryllium in the reaction 9 Be ( a , n) 12 C, which we mix with a suitable a-radiator - used eg 210 Po, 226 Ra, 239 Pu, 241 Am. These mixtures are hermetically closed or sealed in metal or glass containers and serve as portable laboratory sources of neutrons, so-called neutron generators , used eg in neutron activation analysis (3.4 " Neutron activation analysis ").
  Nuclei with an excess of protons are mostly beta + -radioactive or decay by electron capture; according to the method of their production, they are sometimes referred to as cyclotron radionuclides . Some reactions of radionuclide production by proton irradiation are, for example: 18O (p, n) 18 F, 13 C (p, n) 13 N, 11 B (p, n) 11 C, ....; deuterons eg 10 B (d, n)11 C, 56 Fe (d, n) 57Co, ...... Specific methods for producing a number of important radioisotopes are described below in the section " Properties of some of the most important radioactive isotopes ".
Acceleration of negative ions - the possibility of increasing the fluence power of the external beam from the cyclotron
In the cyclotron is a standard accelerated heavy positively charged particles - protons, deuterons, alpha particles, or heavier nuclei such as carbon
12C. For small cyclotrons used for the production of radioisotopes , an important requirement is the high intensity - fluence power - of proton or deuteron beams. At energies around 40MeV, a relatively large current in the beam of about 2-5 mA is achieved. However, this maximum power can only be fully utilized when irradiating an internal target installed inside a vacuum accelerator tube. However, for the routine production of radionuclides, it is more advantageous to lead the particle beam to irradiate the external targets . In classical cyclotrons accelerating positive particles, the resulting beam is extracted with an electrostatic deflector . However, considerable dissipative heat is generated at the partition of this deflector, which is a limiting factor for achieving a high fluency performance of the extracted beam.
  This disadvantage is largely eliminated by the technology of acceleration of negative ions
(1.5, part " Cyclotron ", passage " Acceleration of negative ions ") . Hydrogen or deuterium atoms are supplied with two electrons in an ion source in an electric discharge, creating negative H - or D - hydrogen ions with two electrons. These are then accelerated in the cyclotron. After the necessary acceleration, a thin carbon foil is inserted into the path of negative ions H - in the appropriate path , which " stripping " removing their both light electrons and releases the desired heavy P + or d + . This reverses the direction of curvature in the magnetic field, causing their rapid removal from the field of the cyclotron to the external volume corresponding energy, with minimal thermal dissipation. This leads to considerably higher performance production of radionuclides in the outer disc. This is particularly important for the production of more actions for scintigraphic diagnosis radioisotopes (4.8 " radionuclides and radiopharmaceuticals for scintigraphic ') and a biologically-targeted radionuclide therapy (3.6" radioisotope therapy "), in nuclear medicine.

Modification of irradiated material in the target. Radionuclide purity.
The basis for the production of the required radionuclide is :
Selection of a suitable production nuclear reaction
- the starting nuclide and the type of firing particles and their energy, which implies the required irradiation equipment (nuclear reactor, neutron generator, cyclotron) and its properties.

Preparation of a suitable target
of irradiated nuclide, its chemical form and design. We can irradiate either the starting element directly in elemental form or its suitable compound . Isotopic enrichment is often required irradiated materials in the target - this increases the yield of the reaction and facilitates the subsequent radiochemical separation. Isotopic enrichment of target materials is technologically very demanding and expensive. Therefore, after irradiation and separation of the formed radionuclide, the remaining enriched material is recycled for repeated irradiation.
  The material to be irradiated in the target is used in all three common states :
l   Target in the solid phase consists of a crystalline form (powder or amorphous material), the starting target element or its compound. It is often a metallic form of a given heavier element or its alloy. After irradiation, the target material is used either directly (encapsulated and a closed emitter is formed ) ordissolves in a suitable acid or hydroxide and performs radiochemical separation and preparation of the required chemical form of the radioisotope (or radioisotope designation of a radiopharmaceutical for nuclear medicine).
l A liquid target consists of an ampoule with a starting element or its compound which is liquid at normal temperature or is dissolved in a suitable solvent - most often an aqueous solution . After irradiation, a radiochemical separation is performed in the liquid preparation and the resulting radioisotope is introduced into the required chemical form or radiopharmaceutical.
l
The gas target consists of compressed gas enclosed in a suitable ampoule or chamber  (most often they are inert gases xenon, argon, krypton, ...) . At the end of the irradiation, the radioisotope formed (contained in the enclosure of the chamber or absorbed on the walls) is washed with water or dilute acid; other radiochemical modifications are analogous to the above targets. In the case of isotopically enriched gas, it is recycled for reuse.
  After irradiation, the target material contains not only the desired radionuclide (at least never in 100% concentration), but also a number of other atoms and possibly other radionuclides formed by other (parallel "parasitic") reactions. As a rule, therefore, the irradiated material must be subjected to a demanding procedure of radiochemical separation of the required radionuclides.
Radionuclide purity,   
indicating the percentage ratio of the activity of the desired radionuclide to the total activity of the preparation, is an important parameter of the quality of the produced radionuclide. For technological and medical applications, a high radionuclide purity is generally required , better than 99.9% - or a radionuclide impurity content of less than 0.1%. Radioinuclide impurities can be disruptive during analytical or imaging measurements, or cause increased radiation exposure of the patient
(also discussed 4.8, section " Radionuclides and radiopharmaceuticals for scintigraphy ", passage " Radionuclide purity of radiopharmaceuticals ") .

Secondary radionuclides from decay products. Radionuclide generators.
Some radionuclides are transformed into daughter nuclei, which are not stable, but are again radioactive - they are secondary radioisotopes . Obtaining these secondary radionuclides from the decay products of other radionuclides can be an efficient way to "produce" them.
  This method is of particular importance for short-lived radionuclides , which are formed as daughter nuclei of radionuclides with a substantially longer half-life. The relevant parent radioisotope, prepared by irradiation at an accelerator or reactor, can be easily transported to a remote laboratory, where a daughter short-lived radionuclide can be separated from it continuously or repeatedly, which is thus available for a much longer period of time
(given by the half-life of the parent radionuclide). A device that makes it possible to repeatedly separate a short-lived radionuclide formed by the decay of another longer-lived radionuclide is called a radionuclide generator . Different physico-chemical properties make it possible to separate the parent and daughter elements in the generator. A generator is a system containing a tightly bound parent radionuclide with a longer half-life, from which the resulting daughter radionuclide with a shorter half-life (which is no longer firmly bound to the parent radionuclide carrier) can be separated (detach) either chemically (in the liquid phase), hydrodynamically (elution ) or by blowing with air. The advantage of radionuclide generators is the possibility to use appropriate short-term radionuclides even in workplaces remote from the nuclear reactor or cyclotron. The kinetics of radionuclide generators in terms of decay equilibrium of parent and daughter radionuclides is analyzed in 1.2, section " Mixtures of radionuclides, decay series, radioactive balance ".
  A typical example of a radionuclide generator is a molybdenum-technetium generator
99Mo / 99mTc (described in more detail in 1.2, section " Gamma radiation ", passage " Radionuclide generators ", see also below " Molybdenum-Technetium "), where beta-decay of molybdenum 99Mo (T1/2 = 66 hours) produces metastable technetium 99mTc (T1/2 = 6 hours), which is a pure gamma emitter (Eg = 140keV) and has a wide application in scintigraphy in nuclear medicine - see chapter 4 " Radionuclide scintigraphy ", 4.8 " Radionuclides and radiopharmaceuticals for scintigraphy ", where the principle of operation and technical design of the 99Mo- 99mTc generator is drawn in Fig.4.8.1 . A rubidium-krypton generator used in ventilatory lung scintigraphy is described below in the section " Rubidium-Krypton ". In the field of PET scintigraphy, the germanium-gallium generator 68Ge / 68Ga is finding an increasingly important application (see gallium Ga-68 below) .
  The  table shows several more frequently used radionuclide generators :

Parent radionuclide (T1/2 ) Type of decay Daughter radionuclide (T1/2 ) Type of decay The resulting nuclide
68 Ge (275 d) EC 68 Ga (1.14 hrs) b + , EC, g 68 Zn
81 Rb (4.7 hrs) b + , EC 81m Kr (13 sec) g 81 Cr
82 Sr (25 days) EC 82 Rb (75 sec) b + , EC, g 82 Cr
90 Sr (28 years) b - 90 Y (2.6 days) b - 90 Zr
99 Mo (2.78 days) b - 99m Tc (6 hours) g 99 Tc
113 Sn (115 days) EC 113m In (1.66 hrs) g 113 In
188 W (69.4 days) b - 188 Re (16.98 hrs) b - 188 Os
227 Ac (21.77 years) a, b - series 227 Th (18.7 days) ,
223
Ra (11.4 days)
a, b - series 207 Pb
         
         

"In vivo generators" in nuclear medicine
In nuclear medicine, suitable compound of radionuclides - the radiopharmaceutical - are applied to the internal environment of the organism, where their enter into metabolic processes, and by their biochemical pharmacokinetics may accumulate in certain target tissues and organs. If this radiopharmaceutical is labeled with a radionuclide that converts not to a stable, but to another radioactive isotope with a shorter half-life, then after its uptake, another shorter radionuclide is generated and accumulated in vivo in the target tissue, which "cooperate" with the primary parent radionuclide. If this in vivo generated daughter radionuclide emits g- photons or positrons, can be used for scintigraphic imaging (planar, SPECT, PET - Chapter 4 " Radioisotope scintigraphy ") ; if emits alpha particles or beta- (event. Auger electrons) , can serve (or contribute to) the radionuclide therapy - 3.6 "Radioisotope therapy". This situation, when a longer-term radionuclide applied to the organism by its radioactive transformation creates a daughter short-term radionuclide (or the whole decay series) in the target tissue, is sometimes called an in vivo radionuclide generator - in the context of the above laboratory radionuclide generators .
  A certain problem with in vivo generators is the release - dissociation - of daughter atoms from radiopharmaceutical molecules, leading to impaired stability and redistribution of daughter radionuclides . In addition to chemical processes - changes in the valence (oxidation number) of atoms during radioactive transformation - the backscattering of nuclei during radioactive emission of alpha, beta and partially gamma quanta also contributes to this (1.2, passage " Accompanying phenomena during radioactivity ", paragraph " Backscattering cores ") . The kinetic energy of the backscattering of nuclei usually exceeds the binding energy many times the relevant atoms in the chemical bond *). Radiochemical methods evolve labeling of biomolecules, which penetrate inside the target cells and which are internalized , while the daughter atoms may be sufficiently long to keep in target cells.
*) This manifests itself mainly in alpha-radioactivity. E.g. with an alpha particle emission of 4-7 MeV, a kinetic energy of approx. 60-100 keV is transmitted to the daughter nucleus with a nucleon number of approx. 220 by back reflection. The chemical binding energy of the respective atoms in the biomolecules (conjugates, for example with monoclonal antibodies) is only about 2-5 eV.
  A typical example of an in vivo generator used is radium 223 Ra which is applied as a radiopharmaceutical in the form of chloride. It is taken up in bone metastases, in which 223-radium decays "in vivo" with a half-life of 11.4 days by a whole cascade of alpha-transformations (in combination with an insignificant alpha-beta branch) to other short-lived radionuclides: 223 Ra (11.4d .; a ) 219 Rn (4s .; a ) 215 Po (1.8ms .; a ) 211 Pb (36.1min .; b - ) 211 Bi (2.2min .; a ) 207 Tl (4.8min .; b - ) 207 Pb (stab.) - see radium 223 Ra below for details . One complete radioactive transformation of the 223 Ra nucleus in the whole decay series to a stable 207 Pb releases a total nuclear energy of almost 30 MeV, mainly by four alpha-particles, with a high radiobiological effect; gamma photons are also generated, which can be used to gammagraphically monitor the distribution of the radiopharmaceutical. However, radium 223 Ra does not allow chelating bonds to more complex biomolecules such as monoclonal antibodies, so its use is very limited ( 223 Ra-chloride for palliative therapy of bone metastases) .
A more promising radionuclide type " in vivo generator " is thorium 227 Th , which (unlike radio) allows using type macrocyclic ligand DOTA chelating binding of 227 Th with monoclonal antibodies to form radioimmunoconjugates , which are specifically sequester in tumor cells. High energy a particles capable emitted in radioactive transformations, they can effectively destroy these tumor cells - see thorium 227 Th below for details .
   Another radionuclide that could work very well as an in vivo generator in targeted alpha-therapy is actinium 225 Ac, which decays with a half-life of 10 days by a cascade of 4 alpha transformations (in combination with an insignificant alpha-beta branch) to other short-lived radionuclides: 225 Ac(10d .;a) 221 Fr (4.8m .;a) 217 At (32ms .;a) 213 Bi (46 m .;b - ) 213 the (4mwith .;a) 209 Pb (3.3H .;b - ) 209 Bi (Stab.), is released energy about 27 MeV - see actinium 225 Ac below for details . Here, too, the accompanying gamma radiation is generated, which can be used for scintigraphic imaging. Radiopharmaceuticals labeled with 225 Ac (including monoclonal antibodies, eg 225 Ac-Trastuzumab or 225 Ac-PSMA-617) are being tested for the treatment of leucemia, lymphomas, neuroendocrine tumors, gliomas, melanomas, and are very promising in the prostate. This "in vivo generator" method of therapy proves to be significantly more effective than the previously tested application of 213 Bi alone (the disadvantage of which is the short half-life of 46 minutes) .
  Therapeutic use of in vivo radionuclide generatorsis discussed in more detail in 3.6, passage "
Alpha and beta radionuclides for therapy ".

Chemical compounds of radionuclides. Radioisotope marking. Radioactive preparations.
Radioactive nuclei - radionuclides - are normally part of the atoms
(which have the same chemical properties as non-radioactive atoms) that make up the radioactive substance . Only in exceptional cases is it a pure radioactive element , mostly radioactive compounds of own radioisotope atoms with other non-radioactive atoms, often in a mixture with other substances. A radioactive substance specifically prepared for laboratory, technical or medical use is often called a radioactive preparation .
  Natural radionuclides (described above in the section " Natural radionuclides") are dispersed in the natural environment with a very low concentration. The heavy elements uranium-238,235 and thorium-232 are contained in the earth's crust in minerals in the form of oxides, silicates or phosphates. Potassium K-40 is abundant together with normal non-radioactive potassium. Tritium H-3 is in the form of "heavy" water 3 H 2 O, carbon C-14 is in the atmosphere in the form of carbon dioxide 14 CO 2 . In plants, radio-carbon and tritium are incorporated into virtually all biomolecules in cells, and later in animal and human cells.
  A special field of radiochemistry deals with chemical reactions with the participation of radioactive atoms. The targeted chemical attachment of the atoms of a particular radionuclide to the molecules of a given substance is called radioisotope labeling . The labeled substance - preparation - is then mostly used as a radioindicator for various analytical and diagnostic procedures (3.5 " Radioisotope tracking methods " and 4.8 " Radionuclides and radiopharmaceuticals for scintigraphy ") , or as a radiotherapeutic in biologically targeted radioisotope therapy (3.6, section " Radioisotope therapy ") .
  Chemical reactions of labeling with the desired radionuclide generally do not proceed in 100% yield. Therefore, in the resulting preparations, in addition to the required radioactive substance itself, there is always a small amount of unbound activity and possibly other radioactive substances, that have different radiochemical properties and may be disruptive impair the binding specificity of the labeled substance in laboratory, diagnostic or therapeutic applications. In addition to the radionuclide purity discussed above, the radiochemical purity of the preparations is therefore an important quality parameter . It is the share of the declared chemical compound of a given radionuclide in the total activity of the preparation.
  
Part of the generated ionizing radiation is absorbed inside material of the radioactive preparation, self-absorption of radiation in the sample occurs . This absorbed radiation can cause chemical changes in the material (5.1, section " Effects of radiation on the substance ") - radiolysis of the labeled substance by its own radiation (most often beta or alpha). During this radiation decomposition, the required labeled substance decreases and other substances with different properties are formed instead. This worsens the radiochemical purity of the preparation. In particular, radiolabeled complex organic molecules readily undergo radiolysis. The higher the specific activity of the preparation , the faster the radiation decomposition takes place .

Radionuclide decay (transformation) schemes
The so-called transformation schemes are used for a clear and comprehensive presentation of various types of radioactive transformations and energy levels in specific atomic nuclei (Fig. 1.4.6). The parent and daughter nuclei are represented in these diagrams by means of horizontal lines (representing the energy levels of the nuclei), the position of which in the diagram is determined as follows: the proton number Z is on the horizontal axis , the position in the vertical direction is given by the nucleus energy E *). The basic energy state of each nucleus is marked by a thick line , the excited states of the nucleus are drawn in thin commas (with data on energy and possibly other characteristics), at the appropriate vertical height above the baseline. For the basic states of radioactive nuclei, the half-life is indicated , for special purposes event. also other characteristics (eg spin). The basic state of a stable core is sometimes drawn by a combination of a thick solid line with hatching below. Metastable energy levels are drawn by semi-bold dashes with an indication of the lifetime (half-life) of this metastable excited state.
*) In the practical drawing of decay schemes, the exact proportions of energy values and proton numbers are usually do not strictly comply with a positions of lines. Only approximate relations are fulfiled - states with higher energy are drawn more upstairs, lines for a larger proton number Z are more to the right of cores with a smaller Z .
  The radioactive alpha and beta transformation of nuclei is to draw by an oblique arrow to the left or right, connecting the parent and daughter nuclei at their respective energy levels, which takes place in a given process; next to this arrow is writen the type of transformation (
a, b, EC) and the corresponding quantum energy of the radiation. Deexcitation of excited levels, ie isomeric transitions g, are drawn by perpendicular arrows connecting the higher levels with the corresponding resulting lower levels, or with the baseline state of the daughter core. For arrows showing nuclear transformations and dexcitation, their relative representation [%] (probability, intensity) is given - the average number of emitted quanta (alpha, electrons or positrons, photons) per 100 transformations . At the bottom of the decay scheme (below the daughter nucleus line, or to save space in another free space in the figure), the total conversion energy Q [keV or MeV] is listed.
  Close to the horizontal commas showing the fundamental and excited energy states of nuclei, their energies are given in the decay diagrams. The values of this energy are determined relative to the ground state of the daughter nucleus, to which the energy "0" is assigned . The basic state of the parent nucleus then has the energy Q and possibly the excited states of the daughter nucleus have correspondingly lower energies.
Branched transformation 
A more complex situation occurs in the case of branched transformation , when a given parent nucleus is transformed by two different types of radioactivity (with a certain probability) into two different daughter nuclei with different ground state energies - see 1.2, passage "
Mixed (combined) radioactivity - branched transformationsThen we have two different values ??of the total energy of transformation Q and two series of energy levels of daughter nuclei. For each branch of radioactive transformation, energies are calculated independently . The ground state of one daughter nucleus is assigned energy "0" The same is done for the second daughter nucleus in the second branch of the transformation, the parent nucleus then has two different initial energy values, which we attribute to it from the side of the diagram to which the type of transformation is directed. A typical example of this situation can be seen in the decay scheme of 186 Re , 192 Ir , 152 Eu and several others.
  Figure 1.4.6 shows some of the simplest typical decay schemes :


Fig.1.4.6. The simplest typical conversion schemes of radioactivity
a, b+ , b- , b-+ g and branched transformations EC+ b- .

On the far left it is a pure decay a (mechanism according to Fig.1.2.2 in 1.2) , where with the radiation of the particle a (helium nuclei 4 He 2 ) the parent nucleus N A Z transforms into the ground state of the daughter nucleus N-4 B Z-2 about lower energy; the nucleus B is shifted to the left by two places, as it corresponds to the proton number Z-2, and down according to the energy difference. For the arrow (a double arrow is used for the alpha) showing the transformation itself, the type of transformation and the corresponding quantum energy of the emitted radiation are indicated.
  Next to it is the conversion scheme of pure radioactivity
b+ ( NA Z N B Z-1 + e + + n ), where the daughter nucleus B is shifted by one place to the left relative to the parent nucleus A , which corresponds to a reduction of the proton number by 1.
  Furthermore, Fig. 1.4.6 shows the decay scheme of pure radioactivity
b- ( N A Z N B Z + 1 + e - + n, according to Fig.1.2.3 in 1.2), where the parent core A is transformed into the basic state of the daughter core B , shifted by one place to the right.
  For simplicity, we have so far disregarded the fact that the net conversion of
a or b to the basal level of the daughter nucleus occurs in only a small percentage of cases; usually the daughter nucleus is formed in an excited state, followed by deexcitation - combined radioactivity a + g or b + g . The penultimate decay scheme in Figure 1.1.5 on the right represents an example of the radioactivity b of a specific 137Cs nucleus , which with a half-life T1/2 = 30 years is transformed into a daughter nucleus 137Ba, which is stable. Only about 6.5% of cases go to the basal state of barium, while as many as 93.5% of cases go to the excited state of the nucleus 137Ba with an energy of 662 keV, shown by a horizontal comma. The vertical down arrow shows the deexcitation of this excited state by emitting a photon of radiation g with this energy 662 keV (the properties of this important radionuclide 137Cs are described in more detail below in the passage " Cs-137 ") .
  On the far right of Fig. 1.4.6 is an example of the above-mentioned branched radioactive transformation of one parent nucleus by two different types of radioactivity to two different daughter nuclei
(the example is a simplified scheme of radinuclide 186Re, described in more detail below in passage 186 Re ) .
  The decay patterns of some radionuclides are quite complex, with a number of cascading transformations of corpuscular and a number of excited energy levels, between which isomeric transitions occur accompanied by gamma radiation quanta. That correspond to the complex spectra of such radionuclides. Spectrometric analysis of the emitted radiation is then the main method of recognizing the structure of nuclides.
  In the following section " Properties of some of the most important radionuclides " we present specific decay schemes of a number of more important and more frequently used radionuclides, together with their radiation spectra and other properties, including applications :

Properties of some most important radioactive isotopes
Of the large number of radionuclides (now more than 2000 are known), some of which occur in nature, but most are produced artificially, only less than a tenth are important and practical. Here we will get acquainted with some radioisotopes that are particularly interesting or important from the point of view of natural science or for practical applications . We will describe these important radionuclides in more detail with the indication of their properties, decay schemes and radiation spectra *), methods of origin or production and their use. In the introduction to the description of the properties of individual radionuclides, we always make a brief mention of the physico-chemical properties of the relevant elements; although the radiation behavior of the respective radionuclides is
not directly related to these properties (radioactivity is a property of the atomic nucleus, not the electron shell), they are important for radiochemistry of radioisotope preparation and their behavior and distribution in nature, including living organisms, or applications in medicine. In addition, many non-radioactive isotopes are important in nuclear and radiation processes: whether as a source of bombardment particles, as target materials, components of detection media, shielding and collimating materials. For a comprehensive understanding of nuclear and radiation physics, it is useful to reflect all these contexts...
*) Gamma radiation spectrometry
of some used radionuclides we performed at our Department of nuclear medicine in Ostrava-Poruba, within its modest possibilities, in the 70's and 80's on a scintillation NaI (Tl) detector (size 5x5cm) and a semiconductor Ge(Li) detector with the help of a 4096-channel analyzer ICA-70, later using a Canberra-Packard computer analyzer. We no longer have a Ge(Li) detector at our workplace
(ended service...) and the semiconductor spectra below were acquired at the HPGe detector of the spectrometric laboratory of the SJB and SRO regional center in Ostrava-Zbeh with the kind cooperation of colleagues Ing. J.Lušnk and Ing. J.Rada- the author thanks them very much !
  The spectra of soft gamma radiation and characteristic X-rays
(with energies lower than 30 keV, for which the detection efficiency of the coaxial high-volume HPGe detector is already very low) were measured separately on a planar semiconductor detector with a beryllium input window.
Some of these measurements were mostly performed many years ago on analog spectrometers, so we built them into our spectra by scanning and interpolating the original graphs of the spectra - we apologize for event. distortions and degraded quality.
   Many years ago, we tried the beta radiation spectrometry very improvised with the help of plastic scintillators and liquid scintillators, which is definitely not optimal
(unfortunately we never owned a magnetic spectrometer ...). We do not mention continuous spectra of beta radiation for individual radionuclides in our treatise also because they are quite "dull" and uninteresting - visually they are similar to "eggs like eggs", only stretched to higher or shrunk to lower maximum energies. Relevant information from them can be obtained only by demanding computer analysis using the Fermi-Kurie graph method (2.6 " Measurement of beta, proton and neutron radiation. Liquid scintillators."; at that time we calculated it manually and plotted it graphically on graph paper...). Conversion and Auger electrons with discrete spectra of characteristic energies would be interesting, but at our workplace we didn't have an instrument to measuring...


Scintillation and semiconductor detector used in gamma-spectrometry of radionuclides.
Left: Scintillation probe - NaI (Tl) scintillation crystal + photomultiplier with shielding. Middle: Analog-to-digital converter (ADC) and computer (CPU) multichannel analyzer. Right: Semiconductor Ge (Li) / HPGe detector with preamplifier and Dewar vessel with cooling liquid nitrogen.

Common features of gamma-spectra of radionuclides
Despite all the differences between the energy and the intensity of gamma rays emitted by different radionuclides, the gamma-spectra of all radionuclides have some similar features :

In the beginning photon spectrum in low energy are often seen the peaks of the characteristic X-rays, emitted at electron jumps between the inner shells in the excited atomic shells of the daughter element. These excitations of atoms during radioactive transformations occur in two ways :
1. Internal conversion of gamma radiation
(1.2., Passage " Internal conversion of gamma radiation and X "), when electrons from higher energy levels in the atomic shell jump to the vacancies after conversion electrons. Particularly g -fotony low energy (units or tens of keV) to have a high conversion ratio. Also, some isomeric transitions, highly forbidden due to the spin "mismatch" between the excitation and the ground state of the nucleus (an example is the isomeric 131m Xe ), are realized by an internal conversion mechanism.
2. Electron capture
(1.2, passage " Electron capture (EC) "), in which electrons from higher levels of the atom immediately jump to the vacancies after the captured electrons (usually in the K shell). Thus, especially with radionuclides transformed by electron capture, that the characteristic X-rays are highly represented or even dominant (see eg 125 I ).
  In our gamma spectra, measured by scintillation NaI (Tl) and semiconductor HPGe detector, peaks K
a,b of characteristic X-rays are displayed only for medium and heavy radionuclides (for some lighter radionuclides we measured low-energy peaks of characteristic X-rays separately on silicon semiconductor detector as mentioned above). We will present and analyze the characteristic X-rays in our spectra, only if it is significant - it is clearly visible in the spectra and has a radiation significance.
If a radionuclide emits more gamma-ray energies, the strongest gamma-lines are usually in the lower and medium energies (tens to hundreds of keV), while higher energies are usually represented with significantly lower intensity (see "Magnified sections of spectra" below).
Magnified sections of spectra

In our basic spectra we will list only the most important nuclear levels and radiation energies of a given radionuclide, which are used in applications and are measurable by commonly available detection techniques. The peaks of the weakly represented gamma radiation energies are lost in the spectra graphically displayed on a normal scale (given by the height of the most intense peak) in the region around zero values. To display them, we therefore use an enlarged section of the spectrum, shifted above the horizontal axis; while the energies correspond to the basic scale on the horizontal axis. These magnified sections are marked with a magnification sign "
< ", an up arrow and a magnification multiple - eg " < 16 x "- slight magnification, or " << 256 x "- strong magnification. This situation often occurs when the radioactive transformation occurs to a larger number of excited states of the daughter nucleus. Then it is usually more likely to lower energy levels than to higher excited states - the gamma spectra are represented with a higher intensity peaks at lower energy as the high energy peaks are much weaker, are often visible only at high magnification and long acquisition time. This is what they shown in the enlarged section of the spectrum.
Differences in scintillation and semiconductor gamma spectra
If we look at the images below gamma spectra of a number of radionuclides, we can at a glance see some significant differences between spectra measured scintilannm a semiconductor detector:
  Photopeaks for scintillation spectrum are rounded and soft, as if "blurred" - energy resolution is relatively imperfect (approx. 10% for test line 662keV 137Cs) , close gamma-lines merge into one photopeak. The semiconductor spectrum consists of very sharp and narrow peaks - the energy resolution is about 30 times better. Some compact peaks from the scintillation spectrum are decomposed into several gamma lines on the semiconductor spectrum ...
  In scintillation spectrum shows a significantly represented continuous component of Compton scattered radiation, especially in the region of lower energies. This continuous background is disturbing (especially in the "peak" region of the backscatter, which can interfere with the actual gamma peak of the radionuclide being measured) . In semiconductor spectra, the continuous component is strongly suppressed, because better energy resolution leads to narrow and high peaks (while maintaining the same area under the peak) , which automatically leads to a reduction in the relative height of the continuous background on a graphical representation of the spectrum, normalized to the maximum of the peak.
  We can observe some differences in the relative intensity of the peaks, which are caused by different energy dependence of the detection efficiency. The scintillation NaI(Tl) detector also measures the gamma line with high efficiency with energies of about 20-40keV, for which the coaxial HPGe detector (used by us) already has a very low (or zero end) sensitivity. Therefore, for example, characteristic X-rays usually have a significantly lower content on the semiconductor spectrum than on scintillation. For lighter radionuclides, X-ray peaks do not appear at all on this detector. A planar Ge(Li) or Si detector was used to measure them in some spectra.
Author's apology - distortion in the display of spectra

The original measured spectra of radionuclides from a multichannel analyzer (with high energy resolution and a number of details) had to be significantly reduced graphically for capacity reasons to display in our treatise. This often led to geometric distortion of the spectra, especially from semiconductor detectors - for example, to "shrinkage" of the lines of photopeaks, loss of some points in the curves and their disconnection, merging of nearby lines. As far as possible, I tried to "retouch" these distortions and liken the displayed graphs to the original spectrum. However, this has not always been completely successful, I apologize and welcome the comments of colleagues - experts of spectra ...
  The same applies to the display of more complex decay schemes of some radionuclides, where drawing nearby energy levels and arrows of transformations for similar reasons, the energy scales below the horizontal axes of the spectra are only approximate
(we are able to ensure the accuracy of displaying the positions of numerical values not better than about 10%) . For our purposes, however, this does not matter, because the exact values of the energies of the individual peaks, read from the original spectra (uncompressed, in digital form on the spectrometer), are explicitly descripted by the arrows denoting the respective photo peaks.
  The scale on the vertical axes of the measured number of pulses is relative, normalized to the value of 100.10
3 pulses.
  The individual radionuclides are basically listed in the order of proton and nucleon numbers , but with a number of minor exceptions - on the one hand according to the sequence of radioactive transformations (eg radium-223 is listed after radium-226, from which it is prepared), on the second hand, according to the importance and method of use of the respective radioactive isotopes (e.g. cobalt 57-Co is mentioned up to the far more important 60-Co) . If, for a certain element, its radioactive isotope do not "deserve" a separate section by their number or significance, two or three close elements are combined into one passage (eg nitrogen + oxygen + fluorine, chromium + iron, copper + gallium + germanium, transurans) and their isotopes are discussed in mutual context. This is logical especially in the case of continuity of parent-daughter radionuclide relationships (eg rubidium-krypton, molybdenum-technetium, decay series of heavy alpha-radionuclides) .
Diversity of radionuclides
Every radionuclide is certainly something interesting. However, describe in detail the properties of all known radioisotopes would be too lengthy and confusing *)
(and it would certainly go bezond the powers of the author...). Therefore, we do not mention here those radioisotopes that were once or several times, rather accidentally, in the context of the time, used in research of some natural processes, material and biological, or in nuclear medicine, and then no longer used - either because they have their one-off role already fulfilled, or have been replaced in practice by more advantageous radionuclides (which of course we present). We analyze in more detail radionuclides of particular interest from a nuclear and general natural-scientific point of view, or widely used in scientific and technical applications, medicine, industry (especially those that the author personally uses in analytical and measuring methods, or as calibration standards) . This choice may be somewhat subjective - I welcome the comments and suggestions of colleagues ..!..
*) It is not important to deal with, for example, extremely short-lived radionuclides that can not be used in any way - can be interesting at most in terms of nuclear physics, studies of strongly nonequilibrium nuclear configurations .
  For individual radionuclides, we present and display in the spectra mainly relevant energy levels and radiation, which can be detected by available radiometric techniques. Radiation intensity is given numerically in percentages (
eg "gamma 320keV (10%)" means that "10 gamma photons with an energy of 320keV are emitted per 100 conversions of the respective radionuclide" ). A large number of other, low-saturated levels and very poorly represented radiation energies, as well as their other characteristics (such as spin, multipolarity, parity, which are important only for nuclear research) can be found in detailed isotope decay tables. At our workplace, we mainly used the book edition of the " Table of isotopes " by Lederer, Hollander, Perlman (the new electronic version is " http://ie.lbl.gov/toipdf/toi20.pdf " ). Other new detailed tables in the electronic version are " http://ie.lbl.gov/toi/nucSearch.Lund univ. ") and " http://www.nucleide.org " from" Henri Becquerel Laboratory ".
Short-term and long-term radionuclides
One of the main factors determining the importance and use of radionuclides is the half-life . As mentioned above in section "
Natural radionuclides " have these natural radionuclides (primordial and cosmogenic) with very long half-lives, and the vast majority of significant artificial radionuclides used in science and technology or industry have a sufficiently long half-life - months, years, decades or more to allow them to long-term use mainly in the form of closed radiators .
  Exception are some short-term radionuclides used in nuclear medicine , which due to their chemical and pharmacokinetic properties find application in radionuclide diagnostics or therapy in the form of open emitters - labeled radiopharmaceuticals , applied directly to the body
(usually intravenously or orally, see Chapter 4 " Scintigraphy ", 4.9 " Clinical scintigraphic diagnostics in nuclear medicine ") . In this case, the short half-life may be an advantage in terms of the radiation exposure of the organism.
  Such short - lived radionuclides are mainly
technetium 99m Tc (T 1/2= 6 hours) and also light positron radionuclides: carbon 11 C (T 1/2 = 20.4 min.), nitrogen 13 N (T 1/2 = 10 min.), oxygen 15 O (T 1/2 = 122 sec.) and especially fluorine 18 F (T 1/2 = 110min.), which is taken up in the form of 18F-deoxyglucose and accumulates especially in tumor tissues, which are then imaged by positron emission tomography based on the coincident detection of gamma 511keV annihilation radiation (see 4.3 " Tomographic cameras " and 4.8 "Radionuclides and radiopharmaceuticals for scintigraphy , "part" Positron radionuclides "). Their properties, decay schemes and the spectrum of 511 keV are shown below(passage" oxygen, fluorine "). The shortest radionuclides used in nuclear medicine is metastable krypton 81 m Kr with a half-life only 13.1 seconds.

Hydrogen
The lightest and most widespread element in nature (the universe) is hydrogen H 1 ( hydrogenum - water-forming) , whose proton nuclei formed just after the Big Bang in the hadron era of the universe (1.1, part " Cosmic nucleogenesis ") ; accounts for 75% of total mass (baryonic) in the universe. It is the main "fuel" of thermonuclear fusion inside stars (" Gravity and evolution of stars ", part of the "Thermonuclear reaction inside stars") . It is very reactive, so in terrestrial nature it occurs practically only in compounds (elemental hydrogen occurs only in natural gas and volcanic gases) , of which the most important is water H2O. Along with carbon, hydrogen is the most important biogenic element . It has three important isotopes (in total, the isotopes 1 H 1 to 7 H 1 are known ). Basic "light" hydrogen 1H1 (called sometimes protium ) - relative representation of 99.9885 %, "heavy" hydrogen, deuterium, 2 H 1 (0.0115%) and "extra heavy" hydrogen tritium 3 H 1 (cosmogenic nuclide with trace representation), which is already radioactive.
Hydrogen 1 H ,
as already mentioned, the main "fuel" nuclear fusion inside stars. In nuclear technologies, hydrogen nuclei
- protons are main shelling particles in nuclear research, in the preparation of artificial radioisotopes (see above " Production of artificial radionuclides ") , in proton radiotherapy (3.6, section " Hadron radiotherapy ") .
Deuterium 2 H
- a heavier isotope of hydrogen, formed just after the beginning of the universe during
primordial nucleosynthesis (it is analyzed in more detail in the section " Lepton era. Initial cosmological nucleosynthesis " 5.4 monograph "Gravity, black holes and space-time physics ") . Deuterium is another non-radioactive isotope important in nuclear and radiation physics. Deuterium nuclei deuterons d = 2H are often used as shelling particles in cyclotrons. Heavy water is sometimes used as a moderator and coolant in fission nuclear reactors (1.3, section " nuclear reactors ") . Together with tritium, deuterium is most promising fuel for controlled thermonuclear fusion (1.3, section " Merging nuclei "); direct nuclear fusion of hydrogen nuclei 1H = proton in terrestrial conditions we cannot yet perform .
Tritium 3 H
Leaving aside the free neutron (which is
b- -radioactive n o p + + e - + n with a half-life of 13 min., max. energy beta 782keV), the lightest radionuclide is the hydrogen isotope tritium 3 H , which is with a half-life of 12.3 years converts by b- -radioactivity to the basic state of the helium isotope 3He: 3 H 1 3 He 2 + e - + n (its simple decay diagram is on the left in Fig.1.4.7) . Tritium is a pure beta emitter with a relatively low maximum energy of emitted electrons of 18.6 keV (red curve in Fig .1.4.7 on the right) .


Fig.1.4.7. Beta
- - radioactivity of some of the simplest isotopes.
Left: Conversion schemes of tritium
3H, carbon 14C and phosphorus 32P. Right: Continuous beta spectra of these radionuclides.
Note 1: The energy axis is nonlinear and irregular (illustrative only) in order to draw very energetically different spectra .
Note 2: The spectra were measured with a MarkIII Nuclear Chicago instrument with a toluene liquid scintillator (.2.6, section "
Liquid scintillators ", Fig.2.6.2), plotted and (with modifications) interpolated.
Note 3: The shape of the low-energy part of the spectrum (smooth growth from zero values - which is somewhat different from the actual shape of the initial part of the spectrum
b- - cf. 1.2, passage " Difference of energy spectrum b - and b + ", spectrum in the left part of the picture) is affected by low sensitivity of the instrument for low beta energy and electronic signal filtering to reduce noise pulses.

In terrestrial nature, tritium occurs as a cosmogenic radionuclide (see above the section " Natural radionuclides ", or 1.6, part " Cosmic radiation ", passage " Secondary cosmic radiation "). It also arises during the so-called ternary fission of heavy nuclei, especially uranium (1.3, section " Fission of atomic nuclei ") . The tritium content in nature has been significantly affected by human activity in the last few decades. A large increase in the content of 3H in the environment occured in 1960s as a result of tests of thermonuclear weapons in the atmosphere (at thermonuclear explosion of lithium deuteride 6Li2H tritium is formed by by the reaction 6 Li (n, a ) 3H - see 1.3, section " Compounding of atomic nuclei ", passage " Explosive thermonuclear reactions ") . In fission nuclear reactors, tritium is formed in circulating cooling water by the reaction of neutrons with deuterium 2 H (n, g ) 3 H; to a small extent with deuterium contained in ordinary water, more effectively when using heavy water as a moderator and coolant. Furthermore, in cooling water containing boric acid to control the reactivity of the fission reactor, tritium is formed by the reaction of 10 B (n, 2 a ) 3H. During the operation of nuclear power plants, therefore, a certain smaller amount of 3H (in the order of hundredths of cosmogenic tritium) enters the water and gas discharges .
  Tritium is a suitable excitation radionuclide in small electrical sources - beta - voltaic cells
- see 1.3, passage " Radionuclide volta cells ( "atomic batteries").
  For many applications in nuclear physics
(especially for thermonuclear fusion , in the future probably for energy use - 1.3 "Nuclear reactions and nuclear energy", part " Fusion of atomic nuclei ") , in biology and medicine, tritium is produced artificially by reacting neutrons with lithium:  6 Li (n, a ) 3 H, or is obtained from heavy water in reactors.

Helium
The second lightest and most widespread element in the universe, helium He
2 ("sun god element"), formed in the Lepton era after the Big Bang (primordial nucleosynthesis is analyzed in more detail in the " Lepton Era. Primary Cosmological Nucleosynthesis" section 5.4 of the monograph "Gravity, Black Holes and space - time physics"). However, it is rare on Earth - the reasons are given in 1.1, section " Cosmic nucleogenesis ". All helium in terrestrial nature is a product of the radioactive alpha-decay of uranium and thorium. Under normal conditions, helium is a chemically inert gas which, due to the very low liquefaction temperature (-269.9 oC = 4.2 oK) has an important application in cryogenic technology, especially in superconducting electromagnets . It has two stable isotopes: 4 He (98.999863%) and 3 He (0.000137%). Helium-4 is a very strongly bound nucleus, as it has both the proton and neutron shells filled, which are the lowest. Radioactive isotopes of helium have no practical significance, as they are very short-lived *). Of the 7 known radioisotopes of helium, 5 He is the "most stable" (formed by irradiation of beryllium with neutrons: 9 Be 4 + 1 n 0 6 He 2 + 4 He 2), which has a half-life of only 0.81sec! However, in nuclear physics, helium ( 4 He) is important as an efficient cooling medium (superconducting electromagnets of accelerators and tokamaks, cooling of sensitive detectors) and also as a product of thermonuclear hydrogen fusion (1.3 "Nuclear reactions and nuclear energy", part " Fusion of atomic nuclei " ) . Helium nuclei - alpha particles - are the essence of alpha-radioactivity.
*) Diproton: the short-term isotope of helium 2 He 2 , also called diproton 2p, has a certain interest in nuclear physics - consists of two protons, without neutrons. This state is very unstable and breaks down almost immediately by proton emission or beta + decay. A separate diproton was not observed, only in highly excited states, eg 18 No, the simultaneous emission of two protons was observed, which was interpreted as originating from the short-term bound state 2p.

Lithium, Berylium, Boron
Elements of this group, despite being very light, are relatively under-represented in nature for astrophysical reasons . They formed, as primordial elements , in small quantities in a rapidly expanding universe at the end of the Lepton era
(" Lepton era. Initial cosmological nucleosynthesis ") and in later stellar nucleosynthesis they no longer form, but are burned (1.1, part " Cosmic Alchemy - we are descendants of stars! " , passage" Representation of elements in nature " and 4.1 " The role of gravity in the formation and evolution of stars ", part" Evolution of stars " in book "Gravity, black holes, and physics of space ") .
Lithium Li 3 is a very soft light metal from the alkaline group (it is the lightest metal, and the same time the lightest element in a solid state at room temperature) , chemically highly reactive, so they occur in nature only in slouaninch It has two stable isotopes 6 Li (7.5%) and 7 Li (92.5%). Although lithium has no significant longer -lived radionuclides (the longest half-life is 0.84 s. It has 8 Li) , this element is important in nuclear physics. . 6 Li neutron absorber serves as a source material for producing tritium in a controlled thermonuclear fusion (1.3, part " Tokamak ") . A mixture of lithium and deuterium - lithium-6 deuteride 6 Li 2 H was misused as fuel for the "hydrogen" thermonuclear bomb (1.3, part "Fusion of atomic nuclei ", passage " Thermonuclear explosion ") .
Beryllium Be 4 is a hard gray metal that oxidizes easily in moisture; it is rare in nature (approximately 3-10 mg / kg in the earth's crust) in compounds such as emerald . It is used in special alloys in metallurgy. In nuclear physics, its low absorption (high transmittance) is used for low-energy X and gamma radiation - beryllium entrance windows sensitive detectors. Beryllium is also fabricated some sections of tubes in accelerators, in which there is interaction of the particles - to make the flying out particles easier (without significant absorption) to penetrate to the detectors.In a mixture with a-radionuklides, beryllium serves as a laboratory source of neutrons (see, e.g. passage " Neutron radiation and its interaction "in 1.6) . Beryllium has the only stable isotope 9 Be . Of the radioactive isotopes of beryllium, two cosmogenic radionuclides are of some scientific importance:
  Beryllium  7Be , with a half-life of 53.3 days, is converted by electron capture to a stable isotope 7Li - in 89.5% to the ground state, in 10.5% to the excited level of 478keV, during the deexcitation of which gamma radiation of this energy is emitted. The 7 Be isotope is formed in nature by cosmic rays in the atmosphere. These are mainly fission reactions of high-energy protons with nitrogen nuclei 14 N (p, 2 a ) 7 Be or oxygen 16 O (p, 10 B) 7 Be, then nuclear reactions of neutrons with nitrogen nuclei 14 N (n, 8 Li) 7 Be and oxygen 16 O (n, 10 B) 7Be. Its detection is used to study transport processes in the atmosphere. For research purposes in nuclear physics, the 7 Be isotope is artificially prepared by irradiating lithium with accelerated protons in a cyclotron by the reaction 7 Li (p, n) 7 Be. The isotope 7 Be is interesting for nuclear physics in that it first proved the dependence of the rate of radioactive transformation by electron capture on the chemical state of the isotope - see 1.2, section " Electron capture ", passage " Two peculiarities of EC ".
  Beryllium  10 Be is transformed into a stable isotope 10 B by b- radioactivity with a half-life of 1.6.10 6 years in the basic state. In the atmosphere, the action of cosmic radiation creates reactions with released neutrons: 14 N (n, p a ) 10 Be. Atoms of 10 Be are trapped in the atmosphere on aerosol particles and with rainwater reach the earth's surface, where they settle in the soil, oceans and glaciers. Measurement of this 10 Be
deposition (by mass spectrometry), due to its long half-life, is used to monitor some geological and oceanographic processes.
  A very hidden (deep inside massive stars) natural important radionuclide is one very short-lived isotope of beryllium :
  Beryllium 8 Be , due to its extremely short half-life 6.7.10-17 seconds, is completely insignificant from the point of view of "terrestrial" nuclear physics. Almost immediately after its formation, beryllium-8 breaks down into 2 alpha particles (helium nuclei). However, it is very important from the point of view of nuclear astrophysics : via Be-8, nuclear "helium" burns to carbon in the late stages of massive star evolution. In the specific conditions of high temperatures and pressures inside helium-rich massive stars (after "burning out" of hydrogen), even such a short lifetime of 8 Be is enough for the capture of 4 He nuclei in 8 Be to produce a large amount of carbon 12 C - it is discussed in 4.1 " The role of gravity in the formation and evolution of stars ", part " Evolution of stars " passage "Combustion of helium" book " Gravity, black holes and space-time physics ".
Boron B 5 is a semi-metallic element found only in compounds in terrestrial nature and has two stable isotopes: 10 B (19.9%) and 11 B (80.1%). Although boron has no useful radionuclides (all are very short-lived, the longest 0.77s. has 8 B), this element is very important in nuclear technology. The high effective cross section of the isotope 10 B for the absorption of slow neutrons makes it very suitable material for control rods in nuclear reactors , or the addition of boric acid into cooling water for reactivity control (1.3, section " Nuclear reactors ") .

Carbon
Carbon C 6 ( Carboneum ) is a very important element in space (formed by thermonuclear fusion of helium inside massive stars - We are descendants of stars! ) and in terrestrial nature (in the earth's crust about 200-800 mg / kg) . Carbon is a non-metallic element which, in addition to the amorphous form, occurs in several crystalline structures: graphite (graphite) , diamond (cubic structure, forming very hard, optically transparent crystals), fullerene (spherical "molecules" from networks of carbon atoms, e.g. C60 ). In terrestrial nature, it occurs mainly in compounds, the most important of which is gaseous carbon dioxide CO2 (approximately 0.04% in the Earth's atmosphere - it is important for photosynthesis in plants) , and of minerals, calcium carbonate CaCO3 . Carbon is able to form a huge amount of so-called "organic" compounds with hydrogen, oxygen, nitrogen, phosphorus and other elements, often to form very long, branched and cyclic molecules. Thanks to these very diverse combinations, which can react together again to form other complex specific substances, carbon compounds have become the basic building block of living matter - carbon is an essential biogenic element . Carbon has a number of isotopes 8 C - 22 C, of which only two isotopes 12 C (98.93%) and 13 C (1.07%) are stable. Important are two radioisotopes of carbon :
Carbon 14 C
From the radioactive carbon isotope is very important especially radiocarbon
14 C 6 , which is a half-life of 5730 years converts by b- -radioactivity 14 C 14 N + e - + n' to the ground state of nitrogen 14N7 . 14C is a pure beta emitter with a maximum energy of emitted electrons 156.5 keV (blue curve in the right part of Fig.1.4.7 mentioned above in passage 3 H ) . It occurs in nature as an important cosmogenic radionuclide (it is based on the radicarbon method of determining the age of archaeological objects, described above in the section " Radioisotope (radiometric) dating ", passage " Radiocarbon dating method ").
  The content of radiocarbon-14 in nature is also influenced by human activity. To a lesser extent there is a reduction in the content of 14 C in the environment by burning fossil fuels , of which over millions of years, the original content 14C has already disappeared by radioactive decay; Thus, CO2 generated by the combustion of fossil fuels does not contain 14 C and the proportion of natural radioactive 14CO 2 is thus diluted . Nuclear technologies, on the other hand, increase the content of radiocarbon-14 . The 14 C content increased significantly in the 1960s during nuclear weapons tests due to the 14 N (n, p) 14 C nuclear reaction by the effect of neutrons released during the explosion on nitrogen. A smaller amount of radio-carbon 14 C is also formed during the operation of fission nuclear reactors by the nuclear reaction 17 O (n, a ) 14C on oxygen in cooling water and by reacting 14 N (n, p) 14 C on nitrogen dissolved in cooling water; from the cooling water with ventilation, this small amount of 14 CO 2 gets into the air through the ventilation chimneys of the power plant.
  Like tritium, 14 C radio- carbon is produced artificially by neutron activation of 14 N (n, p) 14 C in a nuclear reactor for many applications, especially biological ones, especially tracking methods (3.5 " Radioisotope tracking methods ") .
Carbon 11 C
Another somewhat important radioisotope of carbon is short-lived positron
11C , which with a half-life of 20.36 min. converts mainly by beta + -radioactivity (99.75%) and to a small extent by electron capture (0.25%) to the ground state of boron 11 B. It is used (relatively rarely) in positron emission tomography (4.3 " PET cameras ", 4.8 " Radionuclides and radiopharmaceuticals for scintigraphy ") . The isotope 11 C is prepared in a cyclotron either by irradiating boron with accelerated deuterons in reactions 10 B (d, n) 11 C, 11 B (d, 2n) 11 C (taking place simultaneously with both stable isotopes of natural boron), or by irradiating nitrogen with protons: 14 N (p, a ) 11 C.
  In this connection we will mention three other light positron radionuclides used in positron emission tomography :

Nitrogen, Oxygen, Fluorine
Nitrogen N 7 ( Nitrogenium ) is an inert gaseous element at normal temperatures, forming the main part of the Earth's atmosphere (78% by volume). At -195 C it changes to a liquid state; liquid nitrogen is a very important cryogenic medium. Along with carbon, hydrogen and oxygen, nitrogen is an important biogenic element as part of the amino acids that make up proteins . Nitrogen has two stable isotopes 14 N (99.64%) and 15 N (0.36%). Radioactive isotopes of nitrogen have relatively short half-lives, less than 10 minutes. It is worth mentioning two of them :
Nitrogen
13 N
with a half-life T
1/2 = 9.96 min. converts by beta+ -radioactivity (99.82%) and to a small extent by electron capture (0.18%) to the basic state of carbon 13 C. The 13 N isotope is prepared in a cyclotron either by irradiating oxygen (in water) with accelerated protons by a nuclear reaction of 16 O (p, a ) 13 N, or by irradiating carbon with deuterons in the reaction 12 C (d, n) 13 N. Nitrogen 13 N is occasionally used in positron emission tomography in the form of ammonia and 13 N-labeled amino acids .
Note: Isotope 13N played an important role in the process of studying radioactivity: it was the first artificially prepared radioactive isotope. In 1934, F.Joliot and I.Curie discovered it in experiments with irradiation of boron with alpha particles (from polonium); was formed here by the reaction of 10 B ( a , n) 13 N.
Nitrogen
16 N
with a half-life T
1/2 = 7.13 sec. converts beta-- radioactivity (E b max = 4290keV and 10420keV) to the ground state (28%) and to the highly excited states of 6130keV (67%) and 7115keV (5%) of oxygen 16 O. During deexcitation, high-energy photons 6.13MeV are emitted and 7.1MeV. Isotope 16N is formed by the reaction of 16 O (n, p) 16 N fast neutrons with the basic oxygen isotope 16 O, mainly in the cooling water of the primary circuit of water-cooled nuclear reactors. The activity of the 16 N isotope in the circulating cooling water is proportional to the number of neutrons in the reactor core, i.e. the intensity of the chain fission reaction (the number of fissiones per second) and the thermal power of the reactor. Measurement of 16N activity by means of gamma-detectors attached from the outside to the primary water cooling water circulation pipe can therefore monitor the correct operation of the reactor.
Oxygen O 8 ( Oxygenium )   is a reactive gaseous element at normal temperatures, making up 21% (by volume) of the Earth's atmosphere. Together with carbon and hydrogen, it is the most important biogenic element. It has three stable isotopes: 16 O (99.76%), 17 O (0.04%), 18 O (0.2%). The radioactive isotope 15O is sometimes used in positron emission tomography :
Oxygen 15 O
with a half-life T
1/2 = 122sec. converts by beta+ -radioactivity (99.82%) and to a small extent by electron capture (0.12%) to the basic state of nitrogen 15 N. Isotope 15O is prepared in a cyclotron either by irradiating nitrogen (enriched with the 15N isotope ) by accelerated deuterons in a nuclear reaction of 15 N (d, 2n) 15 O, or by irradiating oxygen with protons in a 16 O (p, pn)15O reaction . Its use in PET is relatively rare due to the short half-life.
Fluorine F 9 is a green-yellow gas at normal temperatures, very reactive, so it occurs on Earth only in compounds. It belongs to the group of halogens - salt-forming elements (Greek halos = salt ) . It is relatively widespread (540mg / kg in the earth's crust) . It has a single stable isotope of 19F. Radioactive isotope 18 F is very widely used in positron emission tomography :
Fluorine 18 F
with half-life T
1/2 = 110min. converts by beta+ -radioactivity (96.86%) and electron capture (3.14%) to the basic state of oxygen 18 O. The isotope 18 F is prepared in a cyclotron most often by irradiating of oxygen (in water enriched with the isotope 18 O) by accelerated protons in reaction 18 O (p, n) 18 F, less often by irradiation of compressed neon with accelerated deuterons by nuclear reaction 20 Ne (d, a ) 18 F. In positron emission tomography PET is mostly used in the form of 18F-fluoro-deoxyglucose (FDG - 4.8 " Radionuclides and radiopharmaceuticals for scintigraphy ", part " Positron radionuclides " ).
Positron radionuclides
All positron radionuclides, if they are contained in the substance environment
(which is practically always) , emit gamma radiation with an energy of 511 keV (1.2, part " Radioactivity b + " ) during the annihilation positrons emitted with electrons e + + e - 2 g (1.2, part "Radioaktivity b+" and 1.6, section "Interaction of charged particles- direct ionizing radiation", Fig.1.6.1 below). The gamma-spectrum of "pure" light positron radionuclides, which we have discussed so far, is formed by a single annihilation e+e- peak 511keV *) with an intensity close to 200% - in 11 C (199.5%), 13 N (199.6%), 15 O (199.7%), 18 F (193.7%) Some other (heavier) positron radionuclides have a positron content of less than 100% and therefore the intensity of annihilation radiation is often significantly lower than 200% - see eg 22 Na (180.7%), 58 Co (29.8%), 64 Cu (35%), 68 Ga (177.8%), 89 Zr (45.6%); other gamma peaks are also present, from nuclear deexcitations.
*) It is interesting that the annihilation gamma peak 511keV is slightly wider in the spectrum, compared to the surrounding "nuclear" photopeaks, due to the Doppler expansion caused by different braking rates of positrons in the substance before annihilation with electrons
(discussed in 1.2, passage " Spectrum gamma radiation ") . This extension is only about 1.2 keV and is manifested only on semiconductor spectra (we have clearly observed them in our detailed spectrometric measurements, but these differences are not visible on the strongly grapfically reduced and contracted spectra shown below ...) .


Conversion schemes of positron radionuclides 11 C, 13 N, 15 O, 18 F and gamma spectrum of their annihilation radiation 511 keV.

Positron radionuclides are used mainly in nuclear medicine in the form of suitable radiopharmaceuticals, which are captured and accumulated especially in tumor tissues, the distribution of which is then imaged by PET positron emission tomography based on the coincidence detection of gamma 511keV annihilation photon pairs (see 4.3 " Tomographic cameras "and 4.8" Radionuclides and radiopharmaceuticals for scintigraphy ", part" Positron radionuclides ") . Of the above-mentioned light positron radionuclides, only fluorine 18 F is widely used , other positron radionuclides (C-11, N-13, O-15) only rarely, due to their short half-life.
  In our treatise we will gradually present a number of other important light, medium and finally heavy nuclides :

Phosphorus, Sulfur
These are important biogenic elements, abundant in the earth's crust, seawater and living organisms.
Phosphorus P 15 (lat. Phosphorus ) is a relatively widespread non-metallic element - content in the earth's crust about 1 g / kg. Phosphorus is a very important biogenic element found in all plant and animal cells. It is a binding phosphate component of genetic biomolecules DNA and RNA, energy molecules adenosine triphosphate, phospholipid cell membranes (5.2, part " Cells - basic units of living organisms ") . It is stored in bones in calcium phosphate, hydroxiapatite.
  Phosphorus has a single stable isotope 31 P. From a number of radioactive isotopes 24-46P most have short half-lives (minutes, seconds, milliseconds) . Due to the longer half-life, only two phosphorus radioisotopes are important :
Phosphorus 32 P 
With a half-life of 14.27 days, is converted by beta - radioactivity (Eb max = 1710 keV) to sulfur 32 S in the ground state, it is a pure beta emitter . In nature , a small amount of the 32P isotope is formed as a cosmogenic radionuclide in the atmosphere by nuclear reactions of secondary neutrons from cosmic rays. It is produced artificially in a nuclear reactor by irradiating of phosphorus in the reaction 31 P (n, g ) 32 P, or by irradiating sulfur-32 with fast neutrons by the reaction 32 S (n, p) 32 P.
  Radioactive
32 P is used as a radioindicator in laboratory methods of molecular biology and genetics for radiolabeling. 32P -phosphate molecular groups are incorporated into genetically important molecules of nucleotides, DNA, RNA, which can then be sequenced and detected radiometrically (autoradiographically) - 2.2, passage " Autoradiography ". 32 P can also be used to diagnose and treat cancer - tumor cells tend to take up more phosphorus compounds than normal cells.
Radiophosphorus 32 P, as a pure beta-radionuclide, was used for the treatment of hematological malignancies ( iv application of about 200-500 MBq in the form of phosphate), especially polycythemia - 3.6 " Radioisotope therapy ", passage "Treatment of hematological diseases of radiophosphorus 32P".
Phosphorus 33 P
is converted with a half-life of 32.97 days by beta
- radioactivity (Eb max = 248 keV) to sulfur 33S in the ground state. Radioactive 33 P is used in similar laboratory applications as phosphorus-32, in methods where lower beta electron energy is preferred (eg better resolution in autoradiography ) .


Conversion schemes of radionuclides 32 P, 33 P, 35 S and their beta spectra (the same note applies to the beta spectrum as in Fig.1.4.7) .

  Sulfur S 16 (lat. Sulfur ) is also highly reactive and therefore occurs in nature mainly in compounds, mainly in sulfides. It occurs as a pure element during volcanic activity. Contents in the earth's crust of about 0.03 to 0.09 %, concentration in sea water of about 900 mg/liter. Sulfur is also an important biogenic element, it is part of amino acids (cysteine, methionine) forming proteins. It has four stable isotopes: 32 S (94.99%), 33 S (0.75%), 34 S (4.25%) and 36 S (0.019%). Of the radioactive isotopes of sulfur, one has a practical application :
Sulfur 35 S
is converted with a half-life of 87.25 days by beta
- radioactivity (Eb max = 167.3 keV) to chlorine 35Cl in the ground state. Like 32 P, 35 S sulfur is formed in small amounts in the atmosphere as a cosmogenic radionuclide. The 35 S isotope is artificially prepared in a nuclear reactor by irradiating chlorine (potassium chloride) with neutrons by reacting 35 Cl (n, p) 35 S. Radioactive sulfur-labeled amino acids 35S-cysteine and 35S-methionine is used in biochemical research to study amino acid metabolism.

Sodium, Potassium
Sodium and potassium are the most common elements of the alkali metals , abundant in the earth's crust, seawater and living organisms. They are
soft (they can be cut with a knife) , light (they float on water) , silvery shiny metals, very reactive (they react particularly violently with water) , so they occur in nature only in compounds.
Sodium Na 11 (lat. Natrium ) is the most common alkaline element - content in the earth's crust 2.4-2.6 , concentration in seawater 10.5 g/liter. Sodium is one of the biogenic elements and is found in all cells of plant and animal tissues, as well as in extracellular fluid, cca 4% of salt NaC l...
It has a single stable isotope of 23Na. Of the radioactive isotopes, sodium-22 is particularly important :
Sodium 22 Na
is converted with a half-life of 2.6 years predominantly by beta
+ -radioactivity (90%, Eb max = 500keV) and partly by electron capture (10%) to 22Ne in the excited state of 1275keV; during deexcitation, gamma photons with the same energy of 1275keV are emitted. Only 0.056% are converted to baseline 22Ne. The isotope 22Na is prepared in a cyclotron either by irradiating magnesium metal with deuterons in the nuclear reaction 24 Mg (d, a ) 22 Na, or by irradiating fluorine with alpha-particles in the reaction 19 F ( a,n) 22 Na.
  The annihilation peak 511 keV (180%) dominates in the gamma spectrum of sodium-22 , in the area of higher energies there is a significant peak 1274 keV (100%).


Conversion scheme and gamma spectrum of sodium 22 Na.

Radionuclide 22 Na is mainly used as a laboratory source of positrons for atomic and nuclear physics (see eg 1.5, section " Antiparticles - antiatoms - antimatter - antisights ", passage " Artificial production of antimatter ") and for material analysis of samples *). For some PET cameras, sealed Na-22 emitters serve as calibration and adjustment sources of 511 keV annihilation gamma radiation (in addition to 18 F samples and Ge 68 -Ga 68 standards ) - see 4.3, section " Positron emission tomography of PET " .
*) Analysis of materials using positrons, so-called positron annihilation spectrometry (briefly described in 3.3, section " Positron annihilation spectrometry ") , is based on the behavior of positrons as they pass through the test substance. The lifetime of the positron is measured , ie the time interval between its formation in beta+ -radioactivity of 22Na (indicated by photon emission 1275keV) and extinction (accompanied by radiation of annihilation photons 511keV) , which can provide information about structural irregularities - dislocations, vacancies, impurities in crystal structure.

 The alkali metal potassium K 19 (lat. Kalium ) is also very reactive and therefore occurs in nature only in compounds. Contents in the crust of about 2.0 to 2.4 %, concentration in sea water of 380 mg/liter. Potassium is also a biogenic element.......
It has two stable isotopes 39 K (93.3%) and 41 K (6.73%). Natural potassium also contains 0.0017 % of the long-lived radioactive isotope 40 K :
Potassium 40 K
is a widespread natural (primary) radionuclide with a very long half-life of 1,25.10
9 years . Decays branched by beta- -radioactivity (89%) to the ground state of calcium 40 Ca and by electron capture (11%) to argon 40 Ar - to its excited state of 1460 keV. Both of these daughter isotopes are stable, further decay no longer continues. The characteristic gamma peak of 1460 keV (10.5%) of potassium is clearly visible in all spectrometric measurements of natural samples with an acquisition time of several hours (cf. Fig . 1.4.2 above in the section " Natural radionuclides ") .


Conversion scheme and gamma spectrum of potassium 40 K.

Scandium
Scandium Sc
21 (the name comes from its discovery in Scandinavia - L.F.Nilson, 1879, Sweden) is a silvery white soft and light metal somewhat similar to aluminum, its proportion in the earth's crust is about 5-2mg / kg. It has a relatively small use, it is used in alloys with aluminum . It has a single stable isotope of 45 Sc . Of the about 25 known radioactive isotopes of scandium, 44Sc and 47Sc have promising applications in nuclear medicine :
Scandium 44 Sc
Transforms with a half-life of 3.97 hours, predominantly beta+ -radioactivity (94%, Eb + max = 1474keV) and partially electron capture (5.7%) to 44 Ca in the excited state of 1157keV (higher excited levels of 2656 and 3301 keV are only weakly represented) ; during deexcitation, gamma photons are emitted mainly with this energy 1157keV. The annihilation peak 511keV (188%) dominates in the gamma spectrum of scandia-44 , in the area of higher energies the peak is 1157keV (99.8%); faint higher g -peaks 1499, 2144, 2556 and 3301 keV are only visible at high magnification.


Conversion scheme and gamma spectrum of scandium 44 Sc.

Positron radionuclide 44 Sc has promising use in nuclear medicine for scintigraphic imaging by PET positron emission tomography (see 4.3 " Tomographic cameras " and 4.8 " Radionuclides and radiopharmaceuticals for scintigraphy ", section " Positron radionuclides ") . Trivalent skanium binds well, using proven bifunctional chelating agents of the DOTA type , to vector biomolecules, mainly monoclonal antibodies. Compared to 18 F and especially 68 Ga, a longer half-life of almost 4 hours is also advantageous, allowing imaging even with heavier biomolecules with slower pharmacokinetics. It can also be used theranostically in combination with analogous therapeutic radiopharmaceuticals labeled with 90 Y, 177 Lu, or ideally 47 Sc.
  Its great advantage is the production method : Although it can be produced by nuclear reaction of
44 Ca (p, n) 44 Sc on a small cyclotron, in nuclear medicine workplaces (without the need for a cyclotron) 44Sc can be continuously and long-term obtained by elution from 44Ti / 44Sc generator :
The parent titanium 44Ti for the generator is obtained on a cyclotron by a nuclear reaction of 45 Sc (p, 2n) 44 Ti. In the column of the generator, the parent 44 Ti with a long half - life of 60.4 years is transformed by electron capture into the daughter 44 Sc, which is eluted with a suitable solution (H 2 C 2 O 4 + HCl) . Due to the long half-life of the parent 44 Ti (approximately 130,000 times longer than the daughter 44 Sc) , secular equilibrium is maintained in the generator (see section " Radionuclide Generators ") , so that the long-term 44 Sc o can be eluted every day for many years with the same activity, given by the activity of the default 44Ti ......
  Given these advantageous properties, it can be expected that scandium 44 Sc may gradually replace the existing main PET radionuclides 18 F and 68 Ga ..?..
  A certain disadvantage of
44 Sc is the simultaneous emission of high-energy gamma radiation 1157keV, which increases the radiation dose of patients and PET workers. Therefore, there are considerations about the use of the neighboring radionuclide scandium 43 Sc (T1/2 3.89 hours, beta+ 88%, gamma 373keV (23%)), which has properties similar to 44 Sc, but shows much lower energy and intensity of the accompanying gamma radiation ...
Scandium 47 Sc
With a half-life of 3.35 days, it is converted by beta
- -radioactivity to 47 Ti (which is a stable nuclide) , in 31.6% to baseline and in 68.4% to an excited level of 159 kV. Max. the energy of the beta electrons for both cases is 600keV and 441keV, the mean beta energy is 162keV. The 47Sc gamma spectrum consists of a single 159keV peak (68%).


Conversion scheme and gamma spectrum of scandium 47 Sc.

The 47 Sc isotope can be prepared by neutron reactions 47 Ti (n, p) 47 Sc, 46 Ca (n, p) 47 Ca .. ... 47 Sc .... ... in a nuclear reactor, or in a cyclotron by reactions 48 Ca (p, 2n) 47 Sc, 46 Ca (p, g ) 47 Sc, ........
  Scandium
47 Sc is a promising beta- radionuclide for therapy in nuclear medicine. In this case, the gamma radiation of 159 keV can advantageously be used for scintigraphic imaging (planar / SPECT) and monitoring of radionuclide therapy. Sequence 44 Sc /47 Sc can be an excellent teranostic isotope pair for PET imaging + radionuclide therapy.

Chrome, Iron
Chromium Cr 24 is a light white hard metal, resistant to corrosion. It is relatively abundant in terrestrial nature (in the earth's crust about 0.1-0.2 g / kg) . It is mainly used in metallurgy as an alloying additive or for plating. It has 4 stable isotopes: 50 Cr (4.35%), 52 Cr (85.8%), 53 Cr (9.5%), 52 Cr (85.8%), 54 Cr (2.37%) . Of the radioactive isotopes, one found practical application :
Chromium 51 Cr
It is converted with a half-life of 27.7 days by electron capture to the stable isotope
51 V - in 90% of the transformations it is to the ground state and in 10% to the excited state 320keV, during the deexcitation of which gamma photons of the same energy are emitted. The very simple gamma spectrum of chromium-51 consists of a single 320keV photopeak (10%). Compared to most other beta (EC) -gamma radionuclides, 51-chromium is, in terms of activity, a relatively weak gamma emitter, about 10 times weaker than cesium 137 Cs, cobalt 60 Co or radioiodine 131 I. Isotope 51 Cr is prepared by nuclear reaction 50Cr (n, g)51Cr by irradiating chromium (enriched to about 80% with the isotope 50 Cr) by neutrons in a nuclear reactor.


Decomposition scheme and gamma spectrum of chromium
51 Cr.

The radionuclide 51 Cr is used as a tracer radioindicator in some applications in industry, geology and nuclear medicine. In nuclear hematology, 51 Cr-chroman ions indicate red blood cells , or and white blood cells. Using the autologous erythrocytes labeled in this way, the lifespan (or half-life) of the blood cells and, if appropriate, the place of their destruction (4.9 " Survival and sequestration of erythrocytes . ") . The use of 51Cr in nuclear medicine is almost abandoned.
  Radionuclide 51Cr was too. used several times to track groundwater pathways. A solution of radiochrome was poured into an immersion spring, after which water samples were taken from several nearby watercourses and measured on a sensitive well scintillation detector - whether 51 Cr radioactivity appeared in them, for how long and in what amount .

  Iron Fe 26 ( Ferrum ) is a ferromagnetic metal element, relatively abundant in nature (4-6% in the earth's crust). This well-known metal is a basic construction material in mechanical engineering, construction, electrical engineering and many other technical fields, as well as in household and everyday life. It has four stable isotopes: 54 Fe (5.8%), 56 Fe (91.7%), 57 Fe (2.2%) and 58 Fe (0.28%). Of the many radioactive isotopes of iron, two are of practical importance :
Iron 55 Fe
is converted with a half-life of 2.74 years by electron capture to the ground state of manganese
55Mn. The characteristic X-rays Ka,b with energies around 6keV are emitted. 55 Fe
emitters with sufficiently high activity are used as sources of soft X-rays for X-ray fluorescence analysis of light elements (lighter than manganese), eg in geological survey of rocks.
Iron 59 Fe
It is converted with a half-life of 44.5 days of beta
- -radioactivity to stable cobalt 59 Co, mainly to excited states of 1099keV (53%) and 1292keV (45%). During deexcitation, g radiation is emitted mainly with these two energies (with low representation then 142, 192, 335, 1482 keV). It was used in ferrokinetic tests in hematology in nuclear medicine to study iron metabolism in connection with the processes of red blood cell production in anemia or leukemia ( 4.9.9. , Passage " Examination of iron kinetics with 59 Fe ") . In plant biology, the isotope 59 Fe has been used to monitor the uptake of iron from soil and nutrient solutions and its storage in various parts of plants.

Cobalt
Cobalt Co
27 is a ferromagnetic metal element relatively similar to iron, its proportion in the earth's crust is about 25 mg / kg. Its main use is in metallurgy . It has only one stable isotope 59 Co . The most important cobalt radioisotopes are 60Co and 57Co :
Cobalt 60Co
Of the medium-heavy radionuclides, cobalt
60 Co in particular is widely used as a source of hard radiation with gamma energies of 1173 + 1332 keV for radiotherapy (3.6, part " Isocentric radiotherapy ") , defectoscopy (3.3, part " Radiation defectoscopy ") and other technical application. 60 Co , with a half-life of 5.27 years, is transformed by beta- -radioactivity into excited states of nickel 60Ni (which is a stable nuclide). It is mainly, in 99.88%, the level of 2506keV, which cascades deexcites first to the level of 1332.5keV, which then to the ground state of 60 Ni. The spectrum of gamma radiation is formed by two peaks 1173 and 1332 keV, in the scintillation spectrum the continuous Compton scattered radiation is also significantly shown.
  The
60 Co isotope is prepared by neutron irradiation of cobalt metal in a nuclear reactor by the reaction of 59 Co (n, g ) 60 Co.


Conversion scheme and gamma spectrum of cobalt 60 Co.

Cobalt 57Co
Another important radioisotope of cobalt is
57 Co , which is used as a source of softer gamma radiation 122 +136 keV. 57Co with a half-life of 271.8 days is converted by electron capture to excited levels of 706.4keV (0.18%) and especially 136.5keV (99.82%) of iron 57 Fe. The most saturated level of 136.5 keV is deexcited in 10% to the ground state of 57 Fe and in 85.5% to the level of 14.4keV with the emission of main energy gamma 122 keV . After electron capture, photons of the characteristic X-ray K a,b are emitted during electron jumps between the L and K shells of iron with energies of 6.4-7.1 keV, as well as conversion and Auger electrons. Gamma spectrum 57 Co consists above all of the main peak 122keV (85.5%), with the lower neighboring peak 136keV (11%); in the area of higher energies, a very weak peak of 692keV (0.16%) can be seen only after high magnification .
  Isotope
57 Co is prepared by deuterone irradiation of metallic iron in a cyclotron by a nuclear reaction of 56 Fe (d, n) 57 Co.
  


Conversion scheme and gamma spectrum of cobalt 57 Co.

57Co is used as a source of gamma radiation for Msbauer spectrometry of iron and its compounds (3.4, part " Mssbauer spectroscopy ") . In nuclear medicine, vitamin B12 labeled 57 Co was used to determine the intake of this vitamin by intestinal resorption ( 4.9.9 , passage " Schilling test ") .
  Both mentioned cobalt radionuclides
57,60Co are also used as standard gamma emitters . For the proximity of gamma radiation energy 122keV with energy 140keV 99mTc with point sources 57 Co  they are used as pointers in scintigraphy and planar homogeneous sources 57Co are used to adjust and test the homogeneity of the field of view of scintillation gamma cameras (see " Phantoms and phantom measurements in nuclear medicine ") .
Cobalt 58Co
For radioisotope diagnosis in nuclear medicine in the 60s-80s using cobalt
58 Co , which is a 70.8 day half-life of the electron capture (84%) , and b+ -radioactivity (15%) is converted to the excited states of iron 58Fe - 811keV (84 + 15%) and 1675keV (1.2%). During deexcitation, gamma photons are emitted mainly with an energy of 811keV (99.4%), with a much lower intensity of 864keV (0.7%) and 1675keV (0.5%). In nuclear physics, it is sometimes used as a source of positrons . In nuclear medicine, vitamin B12 labeled 58 Co was used in the 1970s and 1980s , similar to the above 57 Co. All these methods are now abandoned.

Copper, Galium, Germanium, Selenium
Copper Cu29 (Cuprum) is a well-known yellow-red shiny metal with very good electrical and thermal conductivity. The content in the earth's crust is about 50-70 mg / kg, pure metallic copper occurs only rarely, it is mostly found in compounds - sulfides, oxides, in combination with iron compounds and others. In addition to metallurgy (alloys with tin - bronze or zinc - brass) , mechanical engineering and construction, the main use of copper in electrical engineering is due to excellent electrical conductivity and corrosion resistance. Copper has two stable isotopes, 63 Cu (69.15%) and 65 Cu (30.85%). Some radioactive isotopes of copper are sporadically used or tested in nuclear medicine (especially PET scintigraphy) and biochemical studies: 61 Cu (T 1/2 = 3.3 hours, b + , EC), 62 Cu (T 1/2 = 9, 7min., B + , EC), 64 Cu (T 1/2 = 12.7 h, b + , EC), 67 Cu (T 1/2 = 61.8 h, b - , g ). Two copper radionuclides appear promising :
Copper 64 Cu,
which with a half-life of 12.7 hours is converted by beta
+ -radioactivity (17.5%) and electron capture (44%) to the basic (53%) and excited (0.5%) state of 64 Ni; further beta- -radioactivity (38.5%) to the basic state of 64 Zn. ....... In the gamma spectrum of 64 Cu dominates (as with any positron radionuclide) e- e+ annihilation peak 511 keV (35%), in the area of higher energies a weak peak 1345.7keV (0, 47%) can be seen only at a significant magnification .


Conversion scheme and gamma spectrum of copper
64 Cu (sample Cu-64 for spectrometric measurements kindly provided by Mgr.A.epa and Ing.J. ervenk from JV ež)

The positron radionuclide Cu-64 is occasionally used in positron emission tomography ("4.3" Positron emission tomography PET ", 4.8" Radionuclides and radiopharmaceuticals for scintigraphy ", section" Radionuclides and radiopharmaceuticals for PET ") . Complex 64 Cu-ATSM (acetyl methyl-thiosemicarbazone) are rapidly and selectively taken up in hypoxic tissues used for diagnosis of hypoxia myocardium and brain, as also tumor hypoxia. 64 Cu-TETA-octreotide permits PET imaging neuroendocrine tumors. also tested for labeling of monoclonal antibodies, e.g. 64 Cu-DOTA-cetuximab, bombesin peptide .........
Copper 67 Cu
is converted with a half-life of 61.8 hours by beta
- -radioactivity to basic (20%) and excited states of zinc of 64 Zn, during their deexcitation gamma radiation with energies of 91keV (7%), 93keV (16%) is emitted, 185keV (49%); three other higher energies up to 393keV are weak, <1%. .......
....... picture - decay scheme + gamma spectrum ..........
Combination of the designation of the same biochemical carrier with the isotope Cu-64 for the diagnosis of PET and Cu-67 for beta-rays therapy are promising for theranostics in nuclear medicine ....

  Galium Ga 36 is a soft, very easily fusible metal (melts already at 30 C) in a light blue-gray color. It occurs relatively rarely (representation in the earth's crust about 15 mg / kg) . Its main use is in electronics as a component of a number of semiconductor materials in the manufacture of transistors and light emitting diodes (LEDs). It has two stable isotopes 69 Ga (60.1%) and 71 Ga (39.9%). Two of the radioactive isotopes are used :
Galium 67 Ga
With a half-life of 3.26 days, is transformed by electron capture into excited states of
67 Zn with energies mainly 93keV (52.5%), 184keV (22.7%) and 393keV (23.6%), the basic state is only 3%. During deexcitation of the daughter 67 Zn, photons of gamma radiation with energies mainly of 93, 184 and 393 keV are emitted. The gamma radionuclide radiation spectrum of 67 Ga consists mainly of three main lines 93keV (38%), 184kev (21%) and 300keV (17%), the weaker line is 394keV (5%). In the higher energy region, weak peaks of 494, 794 and 887 keV (representation around 0.1%) are visible in the spectrum only at high magnification.


Decomposition scheme and gamma spectrum of gallium 67 Ga.

The 67 Ga isotope is prepared by irradiating zinc or copper in a cyclotron with accelerated protons, deuterons or helium nuclei ( a -particles) by nuclear reactions: 67 Zn (p, n) 67 Ga, 68 Zn (p, 2n) 67 Ga, 67 Zn (d , 2n) 67 Ga, 65 Cu ( a , 2n) 67 Ga.
  67Ga is used in nuclear medicine (in the form of a gallium-citrate complex) to image sites in tissues and organs affected by inflammatory processes or tumor foci (4.8 "Radionuclides and radiopharmaceuticals for scintigraphy ") .

Galium 68 Ga
is converted with a half-life of 67.7 minutes by electron capture (8.7%) and mainly by
b+ -radioactivity (87.9%) to 68 Zn, most often to the ground state (just over 1% of the transformations are to excited states 67 Zn, mainly to the level of 1077keV) . The gamma spectrum of gallium-68 is dominated (as with any positron radionuclide) by e- e+ annihilation peak 511 keV (178%), in the area of higher energies weak peaks 1077 (3%) , 1261 (0.1% ) and 1883 (0.14%) keV are visible only at high magnification .


Conversion scheme and gamma-spectrum of gallium 68 Ga.

Radiopharmaceuticals labeled with 68 Ga are used in nuclear medicine for PET imaging ("4.3" Positron emission tomography of PET ", 4.8" Radionuclides and radiopharmaceuticals for scintigraphy ", passage" Radionuclides and radiopharmaceuticals for PET ") . The 68 Ga isotope is used in workplaces most often obtained from germanium-gallium generators 68 Ge / 68 Ga (mentioned a bit below in the passage " Germanium 68 Ge ", including a germanium phantom for PET cameras) . Galium 68 Ga is to some extent "PET analog" of usual technetium 99mTc for SPECT and planar scintigraphy. Allows chelating binding to a variety of radiopharmaceuticals, including lighter monoclonal antibodies (of Fab fragments) . So far, the most frequently used for display of neuroendocrine tumors (somatostatin receptors - labeled octreotide type 68Ga- DOTATOC and its derivatives) . Very promising seems PET imaging of prostate tumors using labeled prostate membrane antigen 68Ga-PSMA (J591, 617, I & T, ...) , followed by biologically targeted radionuclide therapy using the same antiPSMA monoclonal antibodies, labeled with beta or alpha radionuclides.
  Imaging of peptide receptors expressing gastrin- bombesin receptors , eg with 68Ga-DOTA-PEG2 -bombesin, 68Ga-BZH 3 , is also tested . Furthermore, epidermal growth factor receptors HER using the labeled Fab fragment of trastuzumab , also vascular endothelial growth factor receptors VEGF. 68Ga- Annexin can be used for PET to image apoptosis .
Galium-68 is a very promising diagnostic PET radionuclide, which has - in combination with therapeutic radionuclides  
90 Y, 177 Lu, 225 Ac, 227 Th - high teranostic potential (discussed in 4.9, passage " Combination of diagnostics and therapy - teranostics ") .

  Germanium Ge 36 is a gray-white solid semi-metallic element, which occurs relatively rarely in nature (representation in the earth's crust approx. 5-7 mg / kg) . Its main use is in electronics as a component of a number of semiconductor materials in the manufacture of transistors, diodes, integrated circuits; Germanium semiconductor detectors ( Ge (Li), HPGe - 2.5 " Semiconductor detectors " ) are important for our field of nuclear physics . Germanium has 4 stable isotopes: 70 Ge (20.4%), 72 Ge (27.3%), 73 Ge (7.8%) and 74 Ge (36.7%). Natural germanium also contains 7.83% of the very long- lived radioactive isotope 76 Ge (T 1/2 = 1.7.10 21 years; its radioactivity is negligible, it can be considered almost stable - see below) . Of the radioactive isotopes, we mention three - one practically used, the second used in an interesting experiment and the third remarkable for its "exotic" way of decay:
Germanium 68 Ge
is converted with an half-life of 270.9 days by electron capture to the ground state of the positron radionuclide
68 Ga. Based on this radioactive transformation is a 68Ge / 68Ga radionuclide generator , from which a short-lived radioisotope gallium 68 Ga (half-life of 68 minutes - difficult transport to places outside the cyclotron) can be continuously obtained at nuclear medicine workplaces for use in PET scintigraphy ( 68 Ga mentioned above). ) . The Ge / Ga generator based on the principle of ion chromatography is of a similar type as the known Mo / Tc generator (described below - 99m Tc ). It is a glass chromatographic column in which the parent 68Ge is adsorbed in insoluble form on titanium oxide, aluminum or tin oxide. They tested also "metal-free" carriers in organic basis, such as trihydrohybenzene (pyrogallol) formaldehyde resin , and porous sorbents based on nanomaterials could be promised (zirconium and cerium nanomaterials are being tested). After the radioactive conversion of the 68Ge nuclei to the 68Ga daughter nuclei, the gallium atoms formed are exported from the insoluble bond and can be eluted from the column by weak hydrochloric acid solution (0.1M). Elution can be performed repeatedly (several hundred times), with a correspondingly decreasing activity, the generator can serve for about 1-3 years. Positron gallium-68 is thus operatively and long-term available for clinical use in PET at the workplace of nuclear medicine.
  The sequence
68 Ge -> 68 Ga is also used in closed "germanium" phantoms for calibration and testing of PET gamma cameras (see " Phantoms and phantom measurements in nuclear medicine ", section " Tomographic phantoms ") . The source of 511keV annihilation radiation, detected by a PET camera, is daughter gallium-68 (formed by the interaction of positrons emitted by 68Ga with electrons of the material) , the parent germanium does not participate in the radiation.
  The actual parent isotope
68 Ge is prepared by irradiating gallium isotopes in a cyclotron in nuclear reactions 69 Ga (p, 2n) 68 Ge, 72 Ga (p, 4n) 68 Ge, or 66 Zn ( a , 2n) 68 Ge, resp. by cleavage strip reactions (p, p-xn) by precipitating "x" neutrons from bromine or germanium isotopes.
Germanium 71 Ge
is converted to the ground state
71Ga by electron capture with a half-life of 11.4 days, a characteristic gallium X-ray is emitted. This isotope was used in experiments with radiochemical detection of solar neutrinos using the reaction 71 Ga ( n , e - ) 71 Ge. After radiochemical depletion of the germanium formed, the characteristic X-rays and Auger electrons emitted from gallium atoms are measured after conversion by 71 Ge electron capture (1.2, part " Neutrinos - " ghosts "between particles ", passage " Neutrino detections ") .
Germanium 76 Ge
was previously considered stable isotope. Later experiments have shown that with an enormously long half - life of 1,7,10
21 years, it is transformed by double beta decay b- b- to selenium 75 Se (1.2, part " Radioactivity beta - ", passage " Double beta decay " ). .........

  Selenium Se 34 is a gray-white semi-metallic element, which occurs relatively rarely in nature (representation in the earth's crust approx. 0.005-0.17 mg / kg) . Its main use is in electronics due to its outstanding photoelectric properties - photoelectric cells - and as a component of some semiconductor materials. Selenium has 5 stable isotopes: 74 Se (0.89%), 76 Se (9.37%), 77 Se (7.63%), 78 Se (23.77%) and 80 Se (49.61%) . Natural selenium also contains 8.73% of the very long - lived radioactive isotope 82 Se (T1/2 = 1.087.10 20 years; its radioactivity is negligible, it can be considered practically stable) . Of the radioactive isotopes, one found practical application :
Selenium 75 Se 
, with a half-life of 119.8 days, is converted by electron capture (EC) to a series of excited states of arsenic
75 As, predominantly to an excited state with an energy of 401keV (95.9%); conversions to other higher excited states have a very low intensity (<0.01%) . During cascade deexcitation, about 20 energies of gamma photons are emitted, of which energies of 121, 136, 264, 279 and 401 keV have a more significant intensity.


Conversion scheme and gamma spectrum of selenium
75 Se. Apology: The semiconductor spectrum was measured on an older Ge(Li) detector with degraded properties.

Gamma peaks 121 (17%) , 136 (58%) , 264 (58%) , 279 (25%) and 401 (11%) [keV] dominate in the gamma spectrum 75Se. Many other higher peaks in the range of 400-822keV are so low (<0.01%) that in our weak sample (approx. 3kBq) they did not appear in the spectrum.
  The isotope
75 Se is prepared in a cyclotron by irradiating selenium (enriched in the isotope 74 Se) with neutrons by the reaction 74 Se (n, g ) 75 Se in a nuclear reactor. It is used as a source of gamma radiation in industrial radiographic applications (3.3, section " Radiation defectoscopy ") as an alternative to the iridium 192 Ir described below . 75Se it has a longer half-life compared to iridium and provides a softer spectrum of gamma radiation (it may be suitable for defectoscopic testing of thinner metal layers of about 2-3 mm, where lower gamma energy provides better radiographic contrast) .
  Selenium-75 is rarely used in nuclear medicine in the form of
75Se-selenelethionine , in which the sulfur atom in the amino acid methionine is replaced by a selenium-75 atom. After intravenous administration, the amino acid metabolism of methionine and proteosynthesis are examined. In the 60s-80s, this radiopharmaceutical was used for scintigraphic diagnosis of the pancreas (intake of amino acids in the pancreas is a reflection of the rate of synthesis of digestive enzymes - 4.9.3, passage " Scintigraphy of the pancreas ") .

Rubidium - Krypton -Xenon
Rubidium Rb37 is a light soft shiny metal from the group of alkali metals. It is very reactive, so it occurs in nature only in compounds (representation in the earth's crust about 100-300 mg / kg) . It has a single stable isotope of 85 Rb (72.17%), in the natural rubidium the remaining 27.83% is the primordial radioactive isotope 87Rb (see below) . Of the rubidium radioisotopes, three isotopes with diametrically different half-lives are important :
Rubidium 81 Rb
With a half-life of 4.57 hours, it is converted by electron capture (39%) and
b+ -radioactivity (25%) to excited states of krypton 81Kr. The most common transformation to form the metastable isomer 81mKr with an energy of 191keV and a short half-life of 13 seconds.
The artificially produced isotope
81 Rb is used as the parent generator nuclide for the preparation of the short-term metastable isomer 81mKr for lung ventilation scintigraphy in nuclear medicine (see 81m Kr below ) . 81 Rb is most often prepared by the reaction 82 Kr (p, 2n) 81 Rb by irradiation of krypton (possibly enriched with the isotope 82 Kr) with protons accelerated in a cyclotron.
Rubidium 82 Rb
With a half-life of 1.27 minutes is converted by
b+ -radioactivity (96%) and electron capture (4%) to basal (87%) and to excited states (mainly to the level of 776keV - 8%) of krypton 82 Kr. During deexcitation, more gamma photon energies are emitted, only 776keV energy is more significant. The gamma spectrum of rubidium-82 is dominated (as with any positron radionuclide) by the e- e+ annihilation peak 511 keV (191%), the gamma peak 776keV (13%) and the weaker 1395keV (0.5%) are also visible; only at high magnification are other very faint peaks up to 3900keV visible.
.......picture.........
.................. Spectrum ......
The short-term isotope 82 Rb is obtained by elution from a generator 82 Sr / 82 Rb , whose parent isotope 82 Sr has a half-life of 25.4 days - see passage " Sr-82 ". Rubidium-82 is used experimentally for PET scintigraphy of myocardial perfusion (4.9.4., Passage " Scintigraphy of myocardial perfusion ") . It is applied in the form of chloride 82 RbCl, behaves as an analogue of potassium (similar to thallium 201 Tl ) .
Rubidium 87 Rb 
is a primordial radioisotope of rubidium (27.83% content of natural rubidium). With a very long half-life of 4,81.10
10 years , the b- radioactivity is converted to strontium 87 Sr in the ground state. 85 Rb is used in isotope geochronology to determine the age of minerals and rocks - rubidium-strontium dating (see " Radioisotope dating " above) .
Krypton Kr 36 is a chemically inert rare gas, in the Earth's atmosphere it is found in a concentration of about 0.0001   %, from which it is obtained by fractional distillation of liquefied air. Used to fill light bulbs and discharge lamps. It has 6 stable isotopes 78 Kr (0.36%), 80 Kr (2.29%), 82 Kr (11.6%), 83 Kr (11.5%), 84 Kr (56.99%), 86 Kr (17.28%) . From a number of radioactive isotopes, it has a practical application of especially 81mKr in nuclear medicine and 85 Kr in industrial applications.
Krypton 81m Kr
is a metastable nuclear isomer of krypton-81, which with a short half-life of 13.1 seconds deexcites to its ground state, from 65% of the 191keV gamma photon emissions , from 35% by internal conversion to envelope electron emissions.
81mKr is obtained from the generator 81Rb / 81mKr . The principle of this generator is in the left part of Fig. .... The parent rubidium 81 Rb is fixed in the solid phase in a small column, through which a stream of elution air is passed by means of a fan (air pump with adjustable power). Through the radioactive decay of rubidium-81, the continuously released daughter gas krypton 81mKr is entrained by the passing air and led into a breathing mask , from which the patient inhales a mixture of air and radioactive 81mKr. One -way valves are included in the circumference of the breathing mask , and a mixing valve for outside air is also connected to ensure free breathing. Exhaled air is led to the extinction vessel (volume approx. 30 liters) , from which, due to the very short half-life of 81mKr, practically non-radioactive air emerges (in contrast to the xenon 133 Xe below, which had to be piped outside the building) .
Note: As can be seen from the decay scheme in the right part of the picture, after rapid deexcitation of
81mKr the resulting krypton 81Kr in the ground state is not stable, but is weakly radioactive (see below 81Kr), but due to the long half-life it it does not show in any way (well below the level of the natural radiation background).
  During this examination of pulmonary ventilation , inhaled air with a trace content of radioactive 81mKr enters the pulmonary alveoli , and the emitted gamma radiation of 191keV is scanned by a gamma camera.. The scintigraphic image of the area with reduced activity shows areas of the lung with poor ventilation , where krypton-81m, and therefore no air, does not get (either at all or reduced) - see 4.9.5 " Lung scintigraphy (nuclear pneumology) ".


Generator 81Rb / 81mKr.
Left: Principle of generator operation and scintigraphic examination of pulmonary ventilation. Middle: One of the design arrangements of the Rb-Kr generator. Right: Conversion scheme 81 Rb and 81mKr; in the black field is the scintillation spectrum of gamma radiation 81mKr.

Krypton 81 Kr
is transformed by electron capture to a stable
81 Br with a long half-life of 2.29.105 years . In 99.7%, 81 Br is formed in the ground state, in 0.3% in the excited state 276keV. It occurs in nature in very low trace amounts as a cosmogenic radionuclide.
Krypton 85 Kr
With a half-life of 10.75 years, is transformed by beta- -radioactivity (Eb max = 687keV) to a stable 85 Rb, in 99.7% to the ground state, in 0.44% to an excited state of 514keV. During deexcitation, gamma photons with the same energy of 514keV (0.43%) are emitted, in trace amounts (0.0000022%) then during cascade deexcitation of gamma 362.8keV and 151.2keV. In nature, 85 Kr is formed in very low trace amounts as a cosmogenic radionuclide, but at present a much larger amount is produced in nuclear reactors (beta transformations from the primary fission product 85 As). Due to the longer half-life 85 Kr accumulates in the fuel during reactor operation. A small part of this krypton escapes directly from the reactor, most of it during the reprocessing of nuclear fuel, from where it is released into the atmosphere.


Conversion scheme and gamma-spectrum of krypton 85 Kr
I apologize for the poorer quality of gamma spectra (statistical fluctuations, high background). The spectrum was measured on a lamp with a very low content of Kr-85 in the gas charge. Weak peaks 151 and 363 keV are almost not visible in the natural background (if I can get a stronger Kr-85 sample, the measurement would be repeated) ...

Krypton 85 Kr can be produced in a nuclear reactor by neutron fusion of natural krypton-84: 84 Kr (n, g ) 85 Kr; with formation of a metastable predominantly 85 m Kr to 4.48 with a half hours. deexcituje basic state 85 Kr. In most cases, however, 85 Kr is isolated from fission products of nuclear fuel by the PUREX method.
  Krypton
85 Kr is used in technical practice as an additive to the gas filling of lamps (approx. 10kBq / m3 ), where beta-electron ionization facilitates the ignition of an electric discharge at a lower voltage (3.7, section " Radioactivity in lamps "). Another use is as a tracer gas radionuclide for detecting leaks in hermetic vessels and pipes. Also in various other laboratory applications ... (add ..? ..)

Xenon
is included in this section somewhat
atypically , its proton number and position in the periodic table of elements rank it only after iodine (and before cesium). From our point of view, there are two reasons for this atypical classification: 1. Xenon is an inert rare gas similar to krypton; 2. The most important radioisotopes of krypton ( 81mKr ) and xenon ( 133 Xe ) have their main uses in nuclear medicine: for scintigraphic examination of pulmonary ventilation .
Xenon Xe 54 is a chemically inert rare gas, in the Earth's atmosphere it is found in a concentration of about 5.10-6  %, from which it is obtained by fractional distillation of liquefied air. It is used to fill light bulbs and especially discharge lamps. It has 8 stable isotopes: 124 Xe (0.1%), 136 Xe (0.09%), 128 Xe (1.9%), 129 Xe (26.4%), 130 Xe (4.07%), 131 Xe (21.23%), 132 Xe (26.91%), 134 Xe (10.44%), 136 Xe (8.86%).
Note: Of interest is the above-mentioned stable isotope 129 Xe , which is a daughter product of the radioisotope 129 I and whose increased content in some meteorites is used in the so-called iodine-xenon chronometry, to determine the time of their formation - see above section " Radioisotope (radiometric) dating " , passage " Dating using decayed radionuclides ".
Of the radioactive isotopes of xenon,
133Xe is occasionally used :
Xenon 133 Xe
With a half-life of 5.25 days, is converted by
b- -radioactivity to 133Cs, in 99.1% to an excited level of 81keV, 0.87% to a higher level of 160.6keV and only 0.0092% to an even higher level 383.8keV. During deexcitation, gamma photons with an energy of 81keV (37%), then 79.6keV (0.29%) are emitted , with a very low intensity then higher energies of 160.6keV (0.068%), 302.9keV (0.0058%) and 383.8keV (0.0028%).
The isotope
133 Xe is most often obtained by fission of uranium (enriched in the isotope 235 U) by neutrons in a nuclear reactor. Another possibility is neutron irradiation of natural xenon in a nuclear reactor using the reaction 132 Xe (n,g )133Xe (there is also a metastable 133m Xe, which with a half-life of 2.2 days of gamma 233keV photon emission isomerically deexcites to the ground state 133 Xe) , or neutron irradiation of cesium by the reaction 133 Cs (n, p) 133 Xe.
  Gas xenon 133 Xe is used *) in nuclear medicine for the diagnosis of lung ventilation function - it is described in more detail in 3.11b " Dynamic lung scintigraphy (133-Xenon ventilation) " of the book " Comprehensive evaluation of scintigraphy ".
*) 133Xe was often used mainly in the 80's. Its disadvantages were difficult availability, complicated handling of gaseous xenon and the need for special spirometric breathing apparatus . At this price, however, it allowed a very comprehensive examination of respiratory function . Currently, ventilatory lung scintigraphy is performed mostly with the 81m Kr generator krypton described above.
Metastable xenon 131m Xe
is described below in the section "
Radioiodine 131 I ", passage " Metastable xenon 131m Xe ".

Strontium, Ytrium
Strontium Sr 38 is a relatively soft gray-white shiny metal from the alkaline group. It is highly reactive, in nature it occurs only in compounds, in the earth's crust in the amount of 0.03-0.04%. Strontium occurs in nature in the form of 4 stable isotopes: 84 Sr (0.56%), 86 Sr (9.86%), 87 Sr (7%), 88 Sr (82.58%).
Note .:
Isotope
87 Sr in nature nature is formed by the beta-radioactivity of the rubidium isotope 87Rb - it is radiogenic ; long-term radiometric dating is performed using the ratios of the isotopes 87 Sr, 86 Sr and 87 Rb (see " Radioisotope (radiometric) dating " above) .
  Of the radioactive isotopes of strontium, two are particularly important :
Strontium 89 Sr ,
with a half-life of 50.5 days is converted by
b- -radioactivity from 99.99% to the ground state of yttrium 89 Y (Eb max = 1488keV) and from 0.01% to the excited state of 909keV (during deexcitation, very weak gamma radiation of this energy is emitted ). It is therefore a practically pure beta emitter .


Conversion scheme and gamma spectrum of strontium 89 Sr.
Note: The gamma peak of 514 keV in the middle of the spectrum does not belong to 89 Sr, but comes from a small (approx. 0.01%) radionuclide impurity 85 Sr in the measured sample.

In the gamma-spectrum of 89 Sr we see mainly bremsstrahlung radiation with a continuous spectrum, arising from the interaction of fast beta beta electrons with atoms in the sample material; with a decreasing tendency it stretches up to an energy of about 1000keV. With a longer spectrometric acquisition, a faint gamma-ray photopeak with an energy of 909keV can be seen here when magnified .
When measuring our specific sample (" Metastron ") also showed a peak 514 keV, originating from the radionuclide impurity 85 Sr (its origin is mentioned in the note below) .
  Isotope 89Sr is prepared either by irradiating strontium (enriched in the 88 Sr isotope ) with slow neutrons by the 88 Sr (n, g ) 89 Sr reaction in a nuclear reactor, or by irradiating yttrium with fast neutrons in the 89 Y (n, p) 89 Sr reaction . It can also be radiochemically separated from uranium fission products.
Note:
Typical radionuclide impurities in
89 Sr preparations are 85 Sr (formed by the reaction of n,g with the isotope 84 Sr contained in the target) and 90 Sr , arising from the isotope 88Sr, or abundant in fission products.
  Radioisotope 89Sr in the form of chloride ( "Metastron" ) is used in nuclear medicine for the palliative therapy of bone metastases of the ca prostate and breast (3.6, section " Radioisotope therapy ") .
Strontium 90 Sr
with a half-life of 27.78 years converts
b- -radioactivity to the radioactive yttrium 90 Y (Eb max = 546keV) in the basic state. Isotope 90Sr is formed during the nuclear fission of uranium-235 and plutonium-239 (with a yield of 5.7%) and is isolated from fission products from spent nuclear fuel. Used in thermoelectric radioisotope batteries (along with plutonium-238) . An important use of strontium-90 is in 90Sr / 90Y generators for the preparation of yttrium 90Y in nuclear medicine (see Y-90 below) .
Strontium 82 Sr - Sr / Rb generator
is converted to radioactive rubidium
82 Rb in the ground state by electron capture with a half-life of 25.4 days . The strontium-82 isotope serves as the parent isotope in the 82Sr / 82Rb generator to obtain the short-lived positron radionuclide 82 Rb for use in PET positron emission tomography (see passage "82 Rb" above) .
Yttrium Y39 is a silvery gray metal similar to a group of lanthanides. In terrestrial nature, it occurs only in compounds, in the earth's crust in the amount of about 2-4 mg / kg. Yttrium is used to make luminiscence substances. It has the only stable isotope 89 Y. An important radioactive isotope of yttrium is :
Yttrium 90 Y ,
which with a half-life of 64.1 hours is converted by
b- -radioactivity from 99.9885% to the ground state of 90Zr (Eb max = 2300keV) - is thus a practically pure b- emitter .
Only in a small proportion of 0.017% there are conversions to two excited states 90Zr 1760 (0.017%) and 2190 keV (negligible 0.0000014%). The level of 2190keV transitions to the ground state by gamma-deexcitation (gamma emission at the limits of measurability) . The level of 1760keV cannot be deexcited directly to the ground state, as it is a monopole E0 junction 0+ 0+ (discussed in 1.2, section " Gamma radiation ", passage " Nuclear metastability and isomerism ") ; there may be 2-g emission, internal conversion, or emission of e- -e+ pair - 90Y is therefore also a weak positron emitter .
  The spectrum of 90 Y gamma radiation is dominated by a continuous curve of intense bremsstrahlung radiation , which arises during the interaction of high-energy beta electrons with the sample material (with a decreasing tendency it stretches to an energy of almost 2MeV) . In more detailed measurements with a longer exposure time, it further appears in the spectrum  peak of weak annihilation radiation 511keV (0.006%) from emitted positrons. The higher peaks 1761keV *) and 2186keV are very weakly represented.
*) The 1761keV peak arises mainly by simultaneous detection of both emitted gamma quanta at 2-g deexcitation of the 1761keV level (direct gamma deexcitation is prohibited - E0); therefore he is weak.


Conversion scheme and gamma spectrum of yttrium
90 Y.
When measuring the spectrum of very weak gamma radiation, a sample of yttrium was surrounded by a layer of 2.5 cm plastic for shielding the beta hard electrons.

The Y-90 isotope is obtained mainly from the 90Sr / 90Y generator mentioned above. Alternative production methods are irradiation of yttrium with neutrons in a nuclear reactor 89 Y (n, g ) 90 Y (but has a low effective cross section) , or using a cyclotron by irradiation yttrium with deuterons 89 Y (d, p) 90mY (IT, T1/2 = 3.2h.) 90 Y, or rubidium by alpha-particles 87 Rb ( a , n) 90m Y (IT) 90 Y.
  The main use of the isotope
90 Y as a pure b-radiator, is in therapeutic nuclear medicine (3.6, part " Radioisotope therapy ") , where high-energy beta-particles are used in radioimmunotherapy , palliative therapy of metastases or radiation synovectomy in larger joints. The relatively longer reach of these beta electrons in the tissue allows (thanks to the "crossfire" effect ) the even irradiation of larger tumors, often showing heterogeneous blood flow and hypoxia.
  Weak positron and annihilation radiation has no direct radiation significance, it is completely overwhelmed by intense bremsstrahlung radiation. In principle, however, even a weak 511 kV annihilation radiation can be used to image biodistribution therapeutic radiopharmaceuticals labeled with 90Y using positron emission tomography PET *) with better resolution than single photon scintigraphy (planar, SPECT) using bremsstrahlung. Another option for imaging yttrium biodistribution is PET scintigraphy using the 86 Y positron yttrium mentioned below .
*) The coincidence detection mode strongly suppresses the braking radiation, so that even weak annihilation radiation can be successfully detected. The principle of PET is described in 4.3, section " PET cameras ".
Yttrium 86 Y
With a half-life of 14.7 hours, is converted by
b+ -radioactivity (26%) and electron capture (74%) to strontium 86 Sr at more than 20 highly excited levels. In addition to the e- e+ annihilation peak 511keV (35%), the gamma spectrum of yttrium-86 contains a large number of gamma peaks from deexcitation of 86 Sr levels - 443 (16%), 515 + 580 (5%), 628 ( 33%), 703 (15%), 777 (22%), 836 (5%), 1026 (10%), 1077 (83%), 1115 (31%), 1854 (17%), 1921 (21%) ) keV; at high magnification, a number of other weak peaks of mostly high energies can be seen, up to 3800keV. .................picture...........
.................... conversion scheme, spectrum ........
  Isotope
86 Y is prepared by proton bombardment of a strontium target (highly enriched in the isotope 86 Sr) in a cyclotron reacting the 86 Sr (p, n) 86 Y.
  The  yttrium-86 is yet experimentally indicates diagnostic radiopharmaceuticals for use in positron emission tomography PET as radiotracers for accumulating pharmacokinetics and therapeutic radiopharmaceuticals labeled with
90Y in the organism (isotope Y-90 is a pure beta, its biodistribution is difficult to visualize scintigraphically - via bremsstrahlung) . It's a special example of teranostics (cf. 4.9, passage " Combination of diagnostics and therapy - teranostics ") , where in this case one isotope ( 86Y) of the same element serves as a diagnostic indicator of biodistribution of another isotope ( 90Y) used in therapeutic radiopharmaceuticals - eg in 90Y-conjugate of monoclonal antibodies.

 Zirconium Zr 40 is a silvery-gray metal from the group of transition metals, very chemically resistant. In terrestrial nature, it occurs only in compounds, in the earth's crust in the amount of about 160-200 mg / kg. Zirconium silicate ZrSiO4 is diamond-like in hardness and crystalline structure. Zirconium is mainly used in nuclear reactors (fuel cell encapsulation) , due to its chermic and mechanical resistance and low effective neutron capture cross section (1.3, section " Nuclear reactors ") . Zirconium-niobium alloys have superconducting properties and are used in some superconducting electromagnets.
Zirconium has 4 stable isotopes of
90 Zr (51.5%),91 Zr (11.2%), 92 Zr (17.1%) and 94 Zr (17.4%). Natural zirconium also contains 2.8% of the radioactive isotope of primary origin 96 Zr, which is transformed by double beta decay with a hugely long half-life of 3,9.1019 years. Of the radioactive isotopes of zirconium, one has found application :
Zirconium 89 Zr ,
which with a half-life of 78.4 hours is converted by electron capture (76.2%) and positron radioactivity (22.8%) to a stable 89 Y in the excited state, mainly with an energy of 909 keV (in fractional percent electron capture even to higher levels of 1744, 2530, 2567 and 2622 keV) . In the gamma spectrum of zirconium-89 there is a significant e- e+ annihilation peak 511 keV (46%) (as with any positron radionuclide) and an even stronger gamma peak 909 keV (99%); in the area of higher energies, weak peaks of 1621, 1658, 1713 and 1745 keV are visible only at high magnification .


Conversion scheme and gamma spectrum of zirconium
89 Zr.

The positron radionuclide Zr-89 is used in positron emission tomography ("4.3" Positron emission tomography PET ", 4.8" Radionuclides and radiopharmaceuticals for scintigraphy ", section" Radionuclides and radiopharmaceuticals for PET ") . Due to its slightly longer half-life, 89Zr is suitable for PET imaging of slower biological and physiological processes of high molecular weight compounds, especially radioimmunodiagnostics with bioconjugates of heavier monoclonal antibodies (structure and properties of monoclonal antibodies are discussed in more detail in 3.6, part "Targeted biological therapy - monoclonal antibodies "), which have slower pharmacokinetics, so that when labeled with short-term fluorine-18 or gallium-68, radionuclides would not be sufficient in time to be taken up in tumor foci.
  Test is labeled 89Zr-cetuximab , which blocks activation of the epidermal growth factor EGF-R , which plays an important role in proliferation, differentiation and survival of tumor cells. 89Zr-cetuximab may be used for PET diagnostic imaging of cetuximab uptake in tumor and normal tissues prior to biological immunotherapy. It can also be used theranostically to detect the biodistribution of 90Y- or 177Lu-cetuximab in radioimmunotherapy . Next, the labeled is tested 89Zr-trastuzumab , anti-epidermal growth factor HER2 , involved in proliferation, angiogenesis, and metastasis of cancer cells. 89Zr-bevacizumab , an anti VGEF antibody may display caused by tumor angiogenesis, the vascular endothelial growth factor VGEF. A labeled 89Zr-J591 anti-PSMA monoclonal antibody can be used to image PSMA positive prostate tumors.
Note: A certain problem here may be the strong gamma-peak 909keV, whose lower edge and Compton scattered radiation interferes with the relatively wide working window of the analyzer of the measured annihilation radiation 511keV (this may lead to a deterioration of the image contrast due to false coincidences) ..?..

Molybdenum, Technetium
Molybdenum Mo42 is a relatively rare metal element in terrestrial nature (approximately 1-7 mg / kg in the earth's crust) . It has a number of applications, especially in metallurgy. It occurs in a number of stable isotopes: 92 Mo (11.8%), 924 Mo (9.3%), 95 Mo (16%), 97 Mo (9.5%), 98 Mo (24.1%), 100 Mo (9.6%) *) .
*) Coincidence measurements with semiconductor Ge detectors have shown that the 100 Mo isotope is not completely stable, but with a hugely long half-life of about 8.1018 years, it is converted to ruthenium 100Ru by double beta decay .
  Of the radioactive isotopes of molybdenum, 99Mo is the most important :
Molybdenum 99 Mo  
is converted with a half-life of 66 hours by b- -radioactivity to excited levels of the daughter nuclide technetium 99 Tc (left part of the decay scheme) . In 82% the conversion takes place to a metastable excited level of 142 keV 99mTc with a half-life of 6 hours, in 17% to a higher level of 921keV, which emits g 740keV during deexcitation (via the level of 181keV) .   Molybdenum-99 is prepared in a nuclear reactor in two ways. The first method consists in neutron irradiation of molybdenum (enriched in the isotope 98 Mo) in the reaction 98 Mo (n, g ) 99 Mo. More often, however, 99 Mo is produced by fission of uranium (enriched in the isotope 235 U) with slow neutrons, where one of the fission products is 99 Zr, from which the desired molybdenum-99 is formed by two subsequent b- -conversions: 99Zr(b-, T1/2=2,1s.)99Nb(b-, T1/2=15s.)99Mo.
  Molybdenum
99  Mo serves as the parent radionuclide for obtaining technetium 99mTc in a Mo-Tc generator (see below) .
Technetium
The chemical element technetium Tc 43 is practically non-existent in nature *), as it has no stable isotope (with half-lives of the most stable radioisotopes of technetium 97.98.99Tc - 2.6.106 years, 4.2.106 years, 2.1.105 years - they are not long enough to preserve primordial technetium from a supernova explosion to this day, as is the case with thorium, uranium or potassium-40). Absolutely trace amounts of technetium are formed during the spontaneous fission of uranium-235. In the last few decades, however, a relatively large amount of technetium has been generated during the operation of nuclear reactors (1.3 " Fission of nuclear nuclei ", section " Fission products ") .
*) In Mendeleev's periodic table, the space for atomic number 43 remained empty for a long time. The first isotope of this element was discovered in 1937 during irradiation of molybdenum with accelerated deuterons in a cyclotron of 99 Mo (d, n) 97 Tc. This gave rise to the name "technetium" as an element, whose isotopes can only be prepared by an artificial - technical - way.
Technetium 99m Tc
The most important radionuclide for nuclear medicine is metastable technetium
99mTc (T1/2 = 6 hours), which is a pure gamma emitter with energy Eg = 140 keV (88.5%). With negligibly low intensity, g photons of 2.2 keV, 90keV, 142keV, 233keV and 322keV are emitted (see below). However, conversion and Auger electrons , produced from the atomic shell during the internal conversion of deexcitation transitions, are relatively abundant (the mechanism is described in 1.2, passage " Internal conversion of gamma and X-rays "). These are mainly low-energy electrons 1.6-2.9keV (210%), 14-21keV (2.2%) and also electrons of medium energies 120-140keV (21%). During the internal conversion, jumps between electron levels in the envelope also result in soft characteristic X-rays of 18-21keV (8%).
  
99mTc is obtained almost exclusively by the above-mentioned beta-decomposition of molybdenum 99Mo (T 1/2 = 66 hours) in the so-called Mo-Tc generator . However, it can also be produced directly ("instant" technetium) by proton bombardment of natural molybdenum (enriched in the isotope 100Mo) in a cyclotron using a reaction of 100 Mo (p, 2n) 99mTc - used only rarely.
  
Mo-Tc generators are mostly of the elution type. Molybdenum 99 Mo is absorbed on a support (mostly Al 2 O 3 ) in an " insoluble" oxide form in a "chromatographic" column . After the radioactive conversion of the 99 Mo core to the 99mTc daughter core , the resulting technetium atom is released from an insoluble bond; combines with 4 oxygen atoms to form the anion 99mTcO4- pertechnetate . This daughter product is soluble in water, whereby it can be separated from the starting molybdenum by washing with water - elution (in the picture on the left). Since the elution is performed with physiological saline containing a NaCl salt, the pertechnetate anions are immediately ionically bound to sodium to form sodium pertechnetate Na 99mTcO4 - . In this chemical form we obtain technetium from the elution generator.


Elution
99Mo / 99mTc generator.
Left: Principle functional diagram of the elution generator. In the middle: Technical design of a sterile generator with an evacuated elution vial.
Right: Conversion scheme of molybdenum
99 Mo to technetium 99mTc, deexcitation to 99 Tc and slow transformations to stable ruthenium 99 Ru.

New types of sterile elution generators use an evacuated elution vial , into which, after being "injected" by atmospheric vacuum, the saline solution is automatically sucked through a tube leading from the storage vial through the sorption column of the generator with 99Mo (in middle part of figure). Within a few tens of seconds, the vial is filled with 99mTc eluate .
  A detailed decay scheme of 99mTc is below in the right part of the picture. Default metastable level 142keV (produced after beta-conversion of the 99Mo) isomerically passes first at the level of 140.5 keV, from where it emits primary gamma rays with an energy 140.5 keV. With a very small proportion of 0.02%, there is a direct deexcitation to the ground state, in which energy of 142.7 kV is emitted. Photons of very soft gamma radiation of 2.17 kV are practically not observed, as they are almost 100% subject to internal conversion . The core of technetium 99 Tc in the ground state (after the isomeric transition from 99mTc) is beta-radioactive and with a very long half-life of 200,000 years it is slowly converted to stable ruthenium 99 Ru. In a very small percentage, there is a direct beta-conversion of 99mTc from a metastable level *) to 99 Ru (the basic state of the 99Tc nucleus is "bypassed") - mainly to excited levels 322 and 90 keV 99Ru. Their deexcitation produces g- radiation with energies of 322, 232 and 90 keV, but a very small representation. At 99mTc radioactivity, soft characteristic X-rays with energies of 2-3keV (L-series) and 18-22keV (K-series) are also emitted , as well as a larger number of low-energy conversion and Auger electrons (up to 4 electrons/1 conversion), mostly with energies 1.6-3 keV, smaller amounts 120-140 keV (mentioned above).
*) In this process, the commonly stated energy 142keV of this metastable level with respect to the ground state of 99Tc is not applied , but the energy of 436keV measured with respect to the ground state of the daughter 99 Ru. This is a special case of branched transformation , discussed above in the " Conversion Schemes " section.


Detailed conversion scheme of technetium 99mTc - an important radionuclide in nuclear medicine.
Left: Formation of metastable 99mTc by beta-radioactivity of molybdenum
99Mo. Right: The metastable level of 142 keV, in addition to the dominant deexcitation to the ground state of technetium 99Tc, can with low probability by beta- -radioactivity convert directly to excited levels of ruthenium-99 .

In the standard 99mTc scintillation gamma spectrum (on a scintillation spectrometer or gamma camera) we observe only one significant photopeak of 140keV energy - in the picture on the left (on a semiconductor spectrometer we can distinguish a weak line of 142.7keV with careful long-term measurement) . Weak peaks from the excited levels of 99Ru, arising from 99mTc by "bypass" of 99Tc, especially 322keV, can be seen spectrometrically only after filtering out the strong radiating line 140keV with a layer of about 4-5mm lead; the 740keV of (possible) contaminant 99Mo line is also visible on this filtered spectrum - right part of the figure.
Note : Line 90keV, which is stronger than 322keV, we do not see in this filtered spectrum, because it is completely absorbed by the lead layer.


Gamma-spectrometric measurement of the
99m Tc eluate ( top - scintillation spectrum, bottom - semiconductor spectrum).
Left: Basic gamma radiation spectrum
99mTc. Right: Filtered spectrum of gamma radiation measured through the shielding layer of a 5 mm lead container, in which a very weak g -line 322keV of 99mTc and a gamma line 740 and 778 keV of the contaminant 99Mo can be observed .

Technetium-labeled radiopharmaceuticals (4.8 " Radionuclides and radiopharmaceuticals for scintigraphy ") are widely used in static and dynamic scintigraphy of kidneys, liver, lungs, heart, brain and other organs, as well as in tumor diagnostics (4.9 " Clinical scintigraphic diagnostics in nuclear medicine ") .

Indium, Tin
Indium In 49 is a soft, easily fusible metal (157 C) of light color, relatively rarely present in nature (approx. 0.1 mg /kg in the earth's crust) . It is used for the preparation of low-melting alloys, mirror plating, in electronics in the production of optoelectronic components. It has two stable isotopes, 113 In (4.3%) and 115 In (95.7%).
Tin Sn 50 is also a soft, easily fusible metal (232 oC) of light color, somewhat more prevalent (approx. 2-4 mg /kg in the earth's crust) . It has a number of stable isotopes: ........
  Of the radioactive isotopes of indium and tin, three radionuclides are of some importance :
Indium 111 In 
It is converted with a half-life of 67.4 hours by electron capture to cadmium
111 Cd in the excited state of 416keV, during the cascade deexcitation of which gamma radiation with energies of 171 and 245 keV is emitted (decay scheme in the left part of Fig) . The 111In gamma spectrum consists of two significant photo peaks of the mentioned energies (spectrum in the right part of the picture) ; when measured with high detection efficiency, a weaker summation peak around the energy of 416keV is also visible in the spectrum . 111In is produced by irradiating cadmium (enriched in the isotope 111 Cd) with accelerated protons in a cyclotron by the reaction 111 Cd (p, n) 111In.
  In nuclear medicine
111In quite often used for scintigraphy of tumors and inflammatory foci, for immunoscintigraphy and scintigraphy of liquor pathways (4.9 " Clinical scintigraphic diagnosis in nuclear medicine", "scintigraphy of liquor pathways "...) .


Conversion scheme and gamma spectrum of indium
111 In.

T i n 113 Sn
With a half-life of 115 days, it is converted by electron capture to two excited states of indium
113In: in 98.2% the excited state of indium 113mIn is formed , in 1.8% the level of 647keV, which also passes to the level of 113mIn by emission of the gamma photon 255keV . The radionuclide 113 Sn is produced by irradiating tin (enriched in the isotope 112Sn) with neutrons in a nuclear reactor using the reaction 112 Sn (n, g ) 113 Sn. This radionuclide serves as the parent isotope for obtaining indium 113mIn in the generator 113Sn / 113mIn .
Indium 113m In
Metastable
113mIn with a half-life of 1.66h. deexcites to the ground state of gamma photon emissions with an energy of 392keV. It is obtained from the above-mentioned generator 113Sn / 113mIn. In nuclear medicine, it was used in the 1960s -1980s for similar scintigraphic methods as now 111 In, as well as for examination of the skeleton, brain or kidneys. Later, it was gradually displaced by radiopharmaceuticals labeled with 111 In and 99mTc, whose longer half-lives and lower gamma energies are more suitable for scintigraphy.

Iodine
Element
iodine I 53 of the halogen is highly reactive and occurs in nature only in compounds ; is relatively rarely present (approx. 0.1-5 mg /kg in the earth's crust, in sea water approx. 0.6 mg / l) . In the solid state, they form dark purple leaf crystals, which sublimate directly into the gas phase at atmospheric pressure. Iodine is one of the biogenic elements , it is used mainly by the thyroid gland for the production of hormones, especially thyroxine . It has a number of isotopes in the range 108I - 144I, of which only one 127 I is stable . Iodine is the element with the largest number radioisotopes used in practice, especially for applications in nuclear medicine ; we will mention them here in order of importance :
Radioiodine 131 I
The most important radioisotope of iodine is radioiodine
131 I (T1/2 = 8 days, b- with max. energy 606keV, main energy g 364keV). Radionuclide 131 I is converted (according to the decay scheme in the figure on the left) by b- -radioactivity to excited states of the daughter nuclide xenon 131 Xe, which is already stable (non-radioactive) . The dominant "channel" of beta-conversion is to an excited level of 364.5 keV (89%), which in 81% deexcites to baseline 131Xe a in 6% deexcites to a level of 80keV (which then deexcites to baseline). In 2% the conversion occurs to the excited level of 722keV, in 7% to the level of 637keV, in fractions of a percentage to some other excited levels (including the interesting metastable level 164keV of the daughter isomer 131mXe - see below " Metastable 131m Xe ") .


Conversion scheme and gamma spectrum of radioiodine
131 I.
Note: This spectrum was measured with a "fresh" iodine sample in which the metastable xenon 131mXe had not yet accumulated .

In the scintillation and semiconductor spectrum of gamma radiation 131I is dominated the main photopeak capturing the energy of radiation g 364keV . Towards higher energies, two weaker peaks, 637 and 723 keV, are visible. In the region of lower energies we also see weaker peaks 284 and 80 keV, at the very beginning of the spectrum then the characteristic X-ray Ka,b of xenon 30keV (low-energy lines La,b 4-5keV on a common gamma detector not visible) .
Metastable 131m Xe 
With beta-radioactivity of radioiodine
131 I, one of the excited levels of daughter 131 Xe is a metastable 131mXe level with an energy of 164keV, which deeexcitates to the ground state of the 131 Xe nucleus with a half-life of T1/2 = 12 days ; this excited metastable state can therefore be considered as a separate radionuclide 131mXe . Only 0.38% of 131I decays occur at this metastable level, and in addition, its deexcitation is strongly subject to internal conversion (from 98% ), so only about 0.021% is emitted as 164keV gamma radiation (see below). In a hermetically sealed preparation of 131 I, a radioactive equilibrium between the dynamics conversion of 131I and 131mXe is reached after about 14 days from the production of the 131 I isotope (however, the gaseous daughter xenon continuously escapes from the open sample) . It can be said that each preparation of radioiodine-131 is a mixture of two radioisotopes: the parent beta-gamma-radionuclide 131 I with a half-life of 8 days and the daughter metastable gamma-radionuclide 131m Xe with a half-life of 12 days.
  The faint 164keV photopeak from metastable
131mXe is not visible in the scintillation spectrum of the sample 131 I, because it lies in the Compton main energy scattering region of 364keV (interferes with the backscatter peak) . Even at the semiconductor spectrum, it is not obvious at first glance, it is visible only after a strong enlargement of the spectrum section between 100-200 keV. For a more accurate spectrometric measurement of metastable 131mXe, we devised a small "trick" consisting of the following simple experiment (easily performed in a nuclear medicine workplace) :
  We used a liquid sample of
131I in the form of NaI iodide with an activity of about 100MBq (radioiodine commonly used for thyroid therapy) , hermetically sealed in the vial for about 14 days. We then aspirated air above the surface of the sample, containing daughter xenon gas, into a syringe with a needle; we closed this syringe immediately. In addition to air, the gaseous sample in the syringe thus obtained will also contain daughter xenon-131 containing metastable 131mXe , whose gamma radiation can be measured in a spectrometer - we thus got rid of the interfering parent isotope 131 I *), from which we separated the daughter 131mXe. The resulting sample (with an activity of about 3 kBq) for spectrometric measurement was then prepared by transferring about 1/2 milliliter from the aspirated gas charge in the syringe to a small measuring cuvette.
*) If the gaseous filling contains evaporated gaseous iodine, we can get rid of it by shaking a solution of inactive potassium iodide or sodium hydroxide. In our measurement, however, this was not necessary, the aspirated sample was completely pure , without the slightest trace of iodine 131.
  This measurement also shows that iodine does not evaporate from the sodium iodide solution , because the iodine atoms are bound by a strong ionic bond with sodium atoms. Thus, it is not a true paradigm that when working with open iodide Na 131I, the radionuclide iodine-131 is released ("sublimed") into the air. Only the gaseous radionuclide xenon 131mXe can be released . The situation is different for more complex radioiodine compounds, eg 131I-MIBG, where the binding is not so strong and a certain smaller amount of iodine is released from the compound. In addition to xenon-131m, we can also observe radioiodine-131 in the vapors above the sample (spectrometrically demonstrated).

Conversion scheme and gamma spectrum of metastable xenon 131mXe.
A gaseous sample of 131mXe was obtained by separation from a 131I radioiodine preparate by aspirating the gas above the level of a 131I sodium iodide solution.

According to the transformation scheme in the figure on the left, metastable 131mXe with a half-life of 11.96 days deexcites by isomeric transition (IT) to the ground state of 131 Xe. In less than 2%, it is a direct emission of gamma photons with an energy of 164keV . In 98%, there is an internal conversion (IC) of xenon atom sheath electron emissions, mainly from the K shell (61%), partly also from the L shell (28%) and from higher M, N shells (8%). The conversion electrons emitted in this way then have a number of discrete energies in the range of 129-163.8 keV. Electrons from higher levels immediately jump to the "emptied places" after the conversion electrons, which leads to an intense emission of photons of characteristic X-rays.with discrete energies in the range of approx. 29-34keV. The partial internal conversion of this X-ray also emits Auger electrons with energies of 23-34keV (and also with very low energies of 2.5-5.5keV) .
  In the figure on the right, the resulting gamma spectrum is measured with the
131mXe sample thus separated . The characteristic X-rays (lines Ka,b ) of 30keV xenon, arising due to strong internal conversion during deexcitation of the excited level of 164keV, dominate here. The photopeak of the 164keV 131mXe gamma line itself is significantly lower, but it is very clearly visible in the spectrum, especially in the enlarged section.
Production and use of radioiodine
131 I
Isotope
131I can be obtained by irradiating tellurium with neutrons in a nuclear reactor by reacting 130 Te (n, g ) 131mTe, with subsequent radioactive transformations 131mTe ( g , T1/2 = 30h ..) 131 Te ( b- , T1/2 = 25min.) 131 I. In most cases, however, radioiodine 131I is prepared by separation from fission products 235 U.
  Iodine
131I is of key importance in nuclear medicine for the diagnosis (gamma component) and especially the therapy (beta component) of thyroid disease (4.9.1 " Thyrological radioisotope diagnostics " and 3.6, part " Radioisotope therapy ") . It is also used for targeted radioisotope therapy of neuroendocrine tumors (131I-MIBG) and lymphomas ( 131I-Bexxar) .
  For scintigraphic diagnostics,
131I has a disadvantage in the relatively high radiation exposure caused by irradiation of the tissue with energetic beta particles. Therefore, where iodine is essential, 131 I has recently been replaced by the 123 I isotope for diagnosis (see below). In a number of examinations, even better, eg 99mTc, which is a pure gamma emitter with even much lower radiation exposure.
Iodine 123 I
Another radioisotope of iodine used in nuclear medicine is
123 I . With a half-life of T1/2 = 13.2 hours, it is converted by electron capture to tellurium 123 Te *), mainly to its excited level 159 keV (97%), from which comes the main radiation energy g used for scintigraphy. Gamma radiation emitted during dexcitation from higher energy levels (approx. 400-1000keV) has a very low intensity, so it is practically not applied. Deexcitation transitions in the atomic shell after electron capture further produce intense characteristic X-rays (K a, b ) of 27-31 keV.
*) Daughter tellurium-123 is weakly radioactive , transformed with a very long half-life of 12 billion years by electron capture to antimony (stibium) -123. However, the activity of
123Te in the used preparations (tens of MBq) after the disintegration of 123I is immeasurably low , a million times smaller than the natural background.


Conversion scheme and gamma spectrum of iodine 123 I

Isotope 123 I is prepared by proton or deuteron irradiation of tellurium or xenon in a cyclotron by several nuclear reactions. With tellurium (enriched in the appropriate isotope) it is by reactions 123 Te (p, n) 123 I, 122 Te (d, n) 123 I, or 124 Te (p, 2n) 123 I. A more common method of producing the isotope 123 I is to irradiate xenon (highly enriched in the isotope 124 Xe) protons with an energy of 25 MeV, in which three types of nuclear reactions take place simultaneously: 124 Xe (p, 2n) 123 I - direct formation of 123-iodine ; 124Xe (p, pn) 123 Xe ( b + , EC, T 1/2 = 3.9min.) 123 I; 124 Xe (p, 2n) 123 Cs ( b + , EC, T 1/2 = 5.9min.) 123 Xe ( b + , EC, T 1/2 = 2.08h.) 123 I. After irradiation from the target chamber with xenon in approx. 12 hours (until 123 Xe decomposes to 123 I) the resulting 123 I is separated and the remaining xenon 124 Xe is recycled for reuse.
  By iodine-123 indicates some radiopharmaceuticals for scintigraphy . It is mainly sodium iodide Na
123I for thyroid scintigraphy (4.9.1 " Thyrological radioisotope diagnostics ") . 123I-ioflupane and 123I-IBZM are used for scintigraphy of receptor systems in the brain (4.9.8, section " Scintigraphy of receptor systems in the brain ") . Compared to iodine 131 I, 123 I has a more suitable gamma energy, and since it does not emit beta radiation, it causes a significantly lower radiation exposure for the patient during the examination .

Iodine 125 I
Radioiodine
125 I (X 27 + 31keV, g 35keV) with a half-life T1/2 = 59.4 days is converted by electron capture to an excited level of 35.5keV tellurium 125 Te. Deexcitation to the ground state emits gamma radiation of energy 35.5 keV (6.63%). After electron capture, photons of characteristic X-rays of tellurium Ka 27.2-27.4 keV (100%) and Kb 30.9-31.8 keV (25%) are also emitted; this X-radiation is dominant. In addition, after electron capture, due to the internal conversion of gamma and X, a larger amount of Auger and conversion electrons with energies of 0.7-30 keV (approx. 20 electrons /1 decay) is emitted from the electron shell of the daughter tellurium . The 125 I gamma spectrum shows characteristic X-ray peaks around 30keV and a 35keV gamma peak (they merge into one wider peak on the scintillation detector) and, with good detection efficiency, also a summation peak around 65keV, resulting from coincident detection of gamma + X photons *). When measuring 125 I samples in a well scintillation detector with a detection efficiency of about 80%, the summation peak may even be dominant.
*) During electron capture, there is a jump of electrons in the envelope with the formation of a photon characterized by X-rays and practically at the same time deexcitation of the excited level of 35.5 kV 125 Te with the emission of the gamma photon. Both of these photons then enter the detector at the same time and can be coincidentally detected with the formation of a pulse corresponding to the sum of both energies, about 65keV.


Conversion scheme and gamma spectrum of radioiodine
125 I.

Isotope 125 I is prepared by irradiating xenon (enriched in the isotope 124 Xe) with neutrons in the reaction 124 Xe (n, g ) 125 Xe followed by radioactive conversion 125 Xe ( EC, T 1/2 = 16.9 hours) 125 I.
  Iodine
125 I is used in nuclear medicine for in vitro radioimmunoassay (3.5 " Radioisotope tracking methods ") and in radiotherapy for permanent interstitial brachytherapy (3.6, section " Brachyradiotherapy ") .

iodine 129 I
With a long half-life T
1/2 = 1.57.10 7 years, is converted by beta- -radioactivity to an excited state of 39.6 keV xenon 129 Xe, during the dexcitation of which gamma-photons of the same energy are emitted . Due to the high internal conversion of gamma photons, conversion electrons and strong characteristic X-rays with an energy of around 30-34keV are also emitted (but still not as intense as in the electron capture of iodine-125) .
  129I it also occurs in trace quantities in nature - it is formed in the earth's crust during the fission of uranium, in the atmosphere it is formed as a cosmogenic radionuclide from xenon by reactions caused by cosmic radiation. More recently, 129 I is formed during the fission of uranium-235 and plutonium-238, from where it is released during the reprocessing of spent nuclear fuel. Due to the similarity of the gamma spectra of I-129 and I-125, the 129 I standards are used in the calibration of detection systems for measuring 125 I samples in radioimmunoassay .
Note:
It is interesting to use the radioisotope
129I , resp. analysis of the increased content of its stable daughter isotope 129Xe in some meteorites, in the so-called iodine-xenon chronometry for determining the time of their formation - see above the section " Radioisotope (radiometric) dating ", passage " Dating using decayed radionuclides ".


Conversion scheme and gamma-spectrum of radioiodine
129 I.
The spectrum is very similar to the spectrum of iodine 125 I shown above . Small diference is in the somewhat smaler relative proportion of the characteristic X-ray with respect to the gamma line 39.6keV. Furthermore, the summation peak X (Ka,b ) + g is not present , because the characteristic X-radiation arises here due to the internal conversion of gamma photons, which thereby disappear and instead the emitted photons X have nothing to "coincide" with. With each 129I radioactive conversion , either a 39.6keV gamma photon or an X 30-34keV photon is emitted, never both at the same time.

Iodine 124 I
is a positron radionuclide that, with a half-life of 4.18 days, is converted by beta
+ -radioactivity ( 23%) and electron capture ( 77%) to the ground state (27%) and a number of excited states of 124Te: 603 (30%) , 1325 (6%), 2295 (19%) keV and others. The relatively complex gamma spectrum 124I is dominated by the annihilation e- e+ peak 511 keV (46%), then the gamma peaks 603 (63%), 723 (10.4%), 1326 (1.5%), 1376 (1.7 %), 1509 (3.1%) and 1691 (11%) keV. A number of other weak gamma peaks (up to almost 3000keV) it is visible only at high magnification. At the beginning of the spectrum, weaker Ka,b peaks of 27-31 kV characteristic X-ray tellurium are visible due to electron capture . For applications of 124 I, only positron radiation and the resulting annihilation g- radiation of 511 keV are important.


Conversion scheme and gamma spectrum of iodine
124 I

  Isotope 124 I is prepared in a cyclotron by irradiating tellurium isotopes with protons or deuterons in reactions 124 Te (p, n) 124 I, or 124 Te (d, 2n) 124 I, or 126 Te (p, 3n) 124 I.
    Iodine-124 labeled radiopharmaceuticals are used experimentally in PET positron emission tomography
("4.3" PET positron emission tomography ", 4.8" Radionuclides and radiopharmaceuticals for scintigraphy ", passage " Radionuclides and radiopharmaceuticals for PET "). In nuclear thyrology , Na124I can use when scintigraphy in the thyroid gland , where due to higher sensitivity and resolution of PET compared to planar and SPECT scintigraphy, 124I-PET/CT can improve the detection of metastases and residual thyroid tissue, determination of tumor metabolic volumes and pre-therapeutic dosimetry in radioiodine therapy, accurate measurement iodine intake during treatment.
   Due to the relatively longer half-life
(compared to eg 18F or 68Ga) , 124 I may be suitable for PET imaging of slower biological and physiological processes of high molecular weight compounds. It is especially radioimmunodiagnostics with labeling of heavier monoclonal antibodies with slower pharmacokinetics.
   It is tested marked 124I-MIBG (meta-iodobenzylguanidine) for imaging neuroblastoma and pheochromocytoma (with possible radionuclide therapy 131I-MIBG). It tested further the 124I-beta-CIT (2.beta.-carbomethoxy-3beta- (4-iodophenyl) tropane) for PET imaging of the dopamine transporter in the brain with Parkinson's disease. Labeled iodouracyl 124I-2-deoxyuridine (UdR), through its incorporation into DNA and RNA molecules, shows the potential for tumor growth.
  There are also considerations about the therapeutic use of Auger electrons from
124I (is discussed in 3.6, section "Radioisotope therapy", passage "Beta and alpha radionuclides for therapy ", paragraph" Auger electron therapy ").
Note: A certain problem
of 124I for PET applications is the relatively low proportion of required positrons (23%) and, conversely, the undesirable intense gamma radiation 603keV (63%) often at the same time, which is energetically close to the annihilation radiation of 511 kV - in a relatively wide working window of the analyzer is practically indistinguishable from 511 kV, which can lead to deterioration of image contrast due to false coincidences. Furthermore, the considerably high energy of the emitted positrons around 2100keV, which therefore have a relatively long range of about 5mm, slightly impairs the spatial resolution of the PET image.

Xenon Xe 54 , with its radioactive isotope 133 Xe , has been included above in the " Rubidium-Krypton-Xenon " section, the " Xenon " passage , due to the similarity of the applications. Metastable xenon 131mXe was described above in the section " Radioiodine 131 I ", section " Metastable xenon 131mXe ".

Cesium
Cesium Cs
55 is a light soft silvery yellowish alkali metal, easy to melt, which is very reactive, so it occurs in nature only in compounds, and relatively rarely (about 1-5 mg / kg in the earth's crust). Cesium metal has low energy for electron emission. In atomic and nuclear physics, it is therefore used in photoelectric components, such as photomultipliers - the photocathode is usually an alloy of cesium and antimony (2.4 " Scintillation detection and gamma-ray spectrometry ", part " Photomultipliers ") . The hyperfine structure of electrons in cesium atoms is used in very precise so-called atomic clocks (passage " Exact - ideal - measurement of space and time" in 1.6 "Four-dimensional spacetime and special relativity" in monograph " Gravity, black holes and space-time physics ") .
  Cesium has a single stable isotope
133Cs. Very important is the radioactive isotope of cesium :
Cesium 137 Cs
One of the best known and most widely used radionuclides in general is cesium
137 Cs . It is a b- + g emitter with a single gamma radiation energy of 662 keV . With a half-life of 30.05 years, 137 Cs is converted by beta- -radioactivity to stable barium 137Ba - in 5.6% to the ground state, in 94.4% to an excited level of 662keV (it is worth noting that the level of 662keV is metastable with half-life 2.55 min., which is, however, completely negligible due to the basic half-life of 137Cs 30 years). 137Cs is used as the main standard for gamma-spectroscopy (2.4, part " Gamma radiation spectrometry ") , further for irradiation in radiotherapy (3.6, part " Isocentric radiotherapy ") , in defectoscopy (3.3, part " Radiation defectoscopy ") and in a number of other measuring and technical applications.
  
137Cs is formed during neutron fission of uranium 235 U (or plutonium 239) in a nuclear reactor from the primary fission product of iodine 137I by two transformations beta- : 137 I ( b- , T1/2 = 23s.) 137 Xe ( b- , T1/2 = 3.9min.) 137 Cs; the yield is 6%. 137Cs preparations are obtained by radiochemical separation from fission products ( PUREX method - 1.3 "Nuclear reactions and nuclear energy", passage " Nuclear wastes ") .


Conversion scheme and gamma spectrum of cesium
137 Cs.

Barium
Barium Ba
56 is a soft light metal from the group of alkaline earths, which is very reactive, so it occurs in nature only in barium compounds, and relatively rarely (approximately 0.02-0.04% in the earth's crust). Soluble barium salts are highly toxic. An important mineral compound of barium is barium sulphate BaSO4 called barite , whose aqueous suspension has a relatively high density and effectively absorbs X-rays . It is therefore used as a contrast agent in X-rays of the digestive tract (3.2, section " Contrast agents ") and as a component of barite plasters, which cover the walls of X - ray examination rooms to prevent unwanted radiation into the surrounding areas.
  Natural barium is a mixture of 7 stable isotopes:
130 Ba (0.11%), 132 Ba (0.1%), 134 Ba (2.42%), 135 Ba (6.59%), 136 Ba (7.85 %), 137 Ba (11.23%), 138 Ba (71.7%). Of the radioactive isotopes of barium, only 133-Ba has practical use :
Barium 133 Ba
With a half-life of 10.54 years, is converted by electron capture to excited states
133 Cs; during its deexcitation, photons of g-radiation are emitted mainly with energies of 81, 276, 303, 356 and 384 keV. After electron capture, photons of characteristic X-rays of cesium Ka 30.6-31 keV (60%) and Kb 34.9-36.8 keV (18%) and Auger electrons are further emitted . The 133 Ba isotope is prepared by proton irradiation in a cyclotron by the reaction 133 Cs (p, n) 133 Ba.
  For the proximity of the main energy gamma 356keV 133-barium to the energy 364keV
  131I, barium pointers are also used in some workplaces of nuclear medicine to mark the position and structures in thyroid scintigraphy with radioiodine (4.9.1 " Thyrological radioisotope diagnostics ") . Sometimes 133 Ba is also used as a calibration standard for radiometers.
Note: In the past, the isotope 133-Ba has been tested as a tracer radioindicator to determine radio kinetics in the environment.


Conversion scheme and gamma spectrum of barium
133 Ba.

Samarium
Samarium Sm
62 is a soft silvery metal from the lanthanide group (its discoverer P.E.L.Biosbaudran in 1879 this name derived from mineral samarskit , which y.1847 in South Ural found V.ESamarskij -Bychovec) . In terrestrial nature, it occurs in the form of compounds, the concentration in the earth's crust is about 6 mg /kg. In combination with cobalt, samarium is used to make strong permanent magnets. Samarium has 5 stable isotopes: 144 Sm (3.07%), 149 Sm (13.82%), 150 Sm (7.38%), 152 Sm (26.75%), 154Sm (22.75%). Natural samarium also contains two very long- lived radioactive isotopes 147 Sm (14.99%) and 148 Sm (11.24%) :
Samarium 147 Sm
with a half-life of 1.06.10
11 years is transformed by alpha-radioactivity (Ea = 2.31MeV ) to a basic state of 143 Nb. This primordial radioisotope 147 Sm with its daughter product 143 Nb is used in nuclear geochrology (see " Radioisotope (radiometric) dating " above) .
Samarium
148 Sm
with a half-life of 7.10
15 years is converted by alpha-radioactivity (E a = 1.96MeV) to a baseline of 144 Nb. This primordial radioisotope has no use.
  The isotope samarium-153 is artificially produced:
Samarium 153 Sm
is converted with a half-life of 46.5 hours by beta
- -radioactivity (Ebmax = 808keV) to the stable isotope 153 Eu. Conversions take place in 18.4% to the ground state (Ebmax = 803keV) and further to excited states 153 Eu 103keV (49.4%) and 173keV (31.3%). Only in a small percentage (<0.02%) higher excited states of 270, 585, ...., 764 keV occur. With the gradual deexcitation of 153 Eu, a larger number of transitions take place with the emission of gamma-photons with energies mainly 69.7keV (4.7%) and 103keV (29%). Conversion electrons are emitted by the internal conversion of excited levels and a characteristic X-ray with an energy of 40-48 keV is generated.


Conversion scheme and gamma spectrum of samarium 153 Sm.
Note: In the right part of the spectrum, some gamma peaks from radionuclide impurities 152 Eu and 154 Eu are shown in an enlarged section (a detailed spectrum of radionuclide contaminants is shown in the figure below).

In the gamma spectrum of 153 Sm, in addition to bremsstrahlung, the distinctive 70keV and 103keV photopeaks are evident; peaks of higher energies are visible only at higher magnification. At the beginning of the spectrum, there is a characteristic X-ray with lines Ka,b with an energy of about 45 keV, arising during the internal conversion from excited levels of 172 and 103 keV.
Radionuclide impurities in samarium-153 
In our spectrum of the sample samaria-153
(" Quadramet ") no weak higher gamma peaks are evident, as they are over-radiated with radionuclide Europium contaminants 152 Eu and 154 Eu . The image below shows the gamma spectrum of the long-term contaminants themselves, which was measured with a 3-month-old samarium sample, in which the samarium-153 itself has already completely decomposed, leaving only impurities with longer half-lives :


Gamma spectrum of long-term radionuclide impurities in a 3-month "extinct" samarium sample
153 Sm.
In the spectrum containing a large number of gamma-peaks, we found three radioactive isotopes of europium: 152Eu (T1/2 = 13.5 years; its physical properties and gamma-spectrum are given below in the passage Europium 152 Eu ), 154Eu ( T1/2 = 8.6 years) and 155Eu (T1/2 = 4.7 years). The respective photo peaks of these isotopes are marked according to the color assignment at the top right.

The 153 Sm isotope is prepared in a nuclear reactor by irradiating samarium (enriched with the isotope 152 Sm to 99%) with neutrons by the reaction 152 Sm (n, g ) 153 Sm. From the trace isotope impurities in the target, the above-mentioned radionuclide impurities 152,154,155Eu are also formed by neutron fusion .
  Beta-radiation of samarium-153 with the phosphate ligand EDTMP
(which binds to bone hydroxyapatite at sites of increased osteoblastic activity) is used in nuclear medicine for palliative therapy of bone metastases of the breast and prostate ca (3.6, section " Radioisotope therapy ") .

Europium
Europium Eu
63 is a soft shiny metal from the lanthanum group . In terrestrial nature, it occurs only in compounds and is relatively sparsely represented (approximately 1.2 mg /kg in the earth's crust). The most common use of europium is in luminescent materials . Europium has two stable isotopes 151 Eu (47.8%) and 153 Eu (52.2%) (at 151 Eu was recently discovered small a-radioactivity with an extremely long half-life of about 5.1018 years - in practical terms, but it can considered stable) . Of the radioactive isotopes, europium-152 is somewhat important :
Europium 152 Eu
With a half-life of 13.54 years, it is transformed by a very complex branched disintegration scheme. In 27.9% there is
b- -radioactivity to excited levels of 152 Gd, in 71.9% electron capture (in a small percentage also competitive beta+ -conversion) to excited levels of 152 Sm *). During deexcitation of the excited states of daughter gadolinium-152 and samaria-152, a large amount (almost 100) of gamma-ray photons is emitted, of which photons with energy have significant intensity: 122, 245, 344, 779, 867, 964, 1086, 1112 and 1408 keV. For this large energy range of distinctive gamma lines, 152 Eu is used as a advantageous calibration standard in gamma-spectrometry (Chapter 2 " Detection and spectrometry of ionizing radiation ", 2.4, section " Gamma-ray spectrometry ") .
*) The daughter samarium 152Sm is stable , but the daughter gadolinium 152Gd is slightly radioactive - with a huge long half-life of 1.1.10 14 years, it is converted by alpha-radioactivity to 148Sm (and then with even longer half-lives by two more alpha-conversions to 144 Nd and finally to stable 140 Ce). The radiation of these tertiary radionuclides is completely negligible.
  
The 152 Eu isotope is formed by irradiating europium with slow neutrons in a nuclear reactor in a 151 Eu (n, g ) 152 Eu reaction .


Disintegration scheme and gamma spectrum of europium
152 Eu

Europium 152m Eu
is one of the few metastable nuclei (isomers) that have such different quantum properties from the ground state (especially the spin value) that there is no usual transition to the ground state of
g- radiation photon emissions , but to the radioactive conversion of beta- , beta+ or electron capture, to another adjacent nucleus (1.2, passage " Nuclear isomerism and metastability "). 152mEu does not de-excite at all to basic 152 Eu, but with a half-life of 9.31 hours it is converted from 73% by b- -radioactivity to 152Gd and from 27% by electron capture and b+ to 152 Sm. The 152mEu isotope is formed by irradiating europium in a nuclear reactor by reaction 151 Eu (n, g ) 152m Eu.
  The relatively "exotic" isotope 152mEu has no practical use and in addition to the special non-photon conversion of the isomer, we mention it here also because it was used in 1958 by M.Goldhaber et al. to determine the so-called helicity of a neutrino (1.2, part " Neutrinos - " ghosts "between particles ", passage " Difference between neutrinos and antineutrinos - helicity of neutrinos. Goldhaber's experiment. ") .
Europium 154 Eu 
with a half-life of 8.6 years from 99.8
% is converted by beta- -radioactivity to excited levels of 154 Gd, from 0.2 % by electron capture to excited states of 154 Sm. During deexcitation, gamma radiation is emitted mainly with energies of 123, 248, 592, 723, 996, 1005 keV.
Europium 155 Eu
With a half-life of 4.7 years, is converted
to excited levels and to a baseline state of 155 Gd by beta- -radioactivity . During deexcitation, gamma radiation is emitted mainly with energies of 87 and 105 keV.
Mixed gamma spectrum of europium isotopes
152,154,155Eu can be seen above in the spectrometric measurement of radionuclide impurities in the samarium-153 sample .

Gadolinium
Gadolinium Gd
64 is a ductile shiny metal from the group of lanthaniodes . In terrestrial nature, it occurs only in compounds and is relatively sparsely represented (approximately 6.2 mg /kg in the earth's crust), it is mainly mined from the mineral monazite. Gadolinium has interesting magnetic properties: at lower temperatures below 20 C it is ferromagnetic, at higher temperatures paramagnetic. It is used as a contrast agent in nuclear magnetic resonance MRI. Another use of gadolinium is in luminescent materials in radiology. The 157 Gd isotope has a very high effective cross section (approximately 260,000 bar) for thermal neutron capture, so it is used in some nuclear reactors.
  Gadolinium has six stable isotopes:
154 Gd (2.2%), 155 Gd (4.8%), 156 Gd (20.5%), 157 Gd (15.6%), 158 Gd (24.8%) and 160 Gd (21.9%). Natural gadolinium also contains a natural radionuclide of primordial origin 152 Gd (0.2%) with a very long half-life of about 1014 years (alpha radioactivity is converted to 148 Sm) .
  Of the radioactive isotopes, gadolinium-153 is occasionally used :
Gadolinium 153 Gd
With a half-life of 240.2 days, it is converted by electron capture to
153 Eu in the ground state (4%) and in the excited states of 97keV (38%), 103keV (42%) and 173keV (16%). During dexcitation, gamma photons are emitted mainly with energies of 97 and 103 keV. At the beginning of the spectrum there are significant peaks Ka,b of the characteristic X-ray of europium with energies around 44keV.
The 153 Gd isotope is mostly prepared from europium. Irradiation with neutrons in a nuclear reactor produces a combination of: 153 Eu (n, g ) 152mEu ( b- , T1/2= 92min) 153 Eu 152 Gd; 152 Gd (n, g ) 153 Gd. Or irradiation with alpha-particles in a cyclotron produces a sequence of processes: 151 Eu ( a , 2n) 153 Tb ( b+ , T1/2 = 2,3d) 153 Gd.
  Gadolinium 153 Gd was used as a two-photon source of gamma radiation 103keV and X 44keV in bone densitometry by the DEXA method (3.2, passage " Bone densitometry ") , experiments were also performed using CT. Sometimes they are used gadolinium rods in SPECT scintigraphy for correction of gamma radiation intensity on attenuation during tissue passage (4.3, passage " Adverse effects of SPECT and their correction ", point " Absorption of gamma radiation ") . However, these methods have not worked very well and are mostly already abandoned ...


Conversion scheme and gamma spectrum of gadolinium
153 Gd.

Erbium, Yterbium, Terbium
The names for some lanthanides " terbium, yttrium, erbium, yterbium " originated historically from the Swedish village of Ytterby , near which these elements were first discovered in a feldspar quarry in the minerals gadolinite and monazite.

Erbium Er 71 is a soft silvery shiny metal from the lanthanide group. It is contained in the earth's crust in the form of compounds in a concentration of about 2.5 mg / kg. It has 6 stable isotopes: 162 Er (0.14%), 164 Er (1.6%), 166 Er (33.5%), 167 Er (22.87%), 168 Er (26.98%), 170 Er (14.91%). Of the radioactive isotopes, one has practical significance :
Erbium 169 Er
is an artificially produced radionuclide, which with a half-life of 9.39 days is converted by
b- -radioactivity from 55% to basic (Eb max = 353keV) and from 45% to a low excited state of 169 Tm with energy 8.41keV (at deexcitation emits low-energy radiation g of this energy) . With a very low intensity, an excited state of 118keV arises. Erbium-169 is a practically pure beta emitter , as soft gamma radiation of 8.4 kV is subject to almost 99% internal conversion, especially on the M and N shells of the Tm atom (with significant emission of low-energy conversion electrons 0.7-8.4 keV, approx. 250 %) and line 110, 118keV is primarily very weak.


Conversion scheme and gamma spectrum of erbium 169 Er.
Note: Erbium 169 has only two very weak gamma peaks 110 and 118 keV (indicated by blue arrows in the spectrum). A number of other peaks measured in our spectrum come from small radionuclide impurities that the measured sample of erbium-169 contained. We mainly measured yterbium 169 Yb with peaks: 50.57.59keV (XK a, b Tm), 63, 110, 118, 130, 177, 198, 308 keV (its physical properties and gamma spectrum are given below in the passage Yterbium 169 Yb ). Further samarium 153 Sm: 70, 103 keV (its physical properties and gamma spectrum are given above in the passage Samarium 153 Sm ); erbium 172 Er : 407, 610 keV; lutetium 177 Lu : 113, 208, 250, 321 keV (its physical properties and gamma spectrum are given below in Lutetium 177 Lu ); finally trace amount of thulium 172 Tm : 79, 182, 1093, 1120, 1387, 1466, 1529, 1608 keV. Due to the very weak gamma radiation of the own 169 Er, even a small amount of these impurities (<0.1%) is significantly reflected in the spectrum, even the own gamma erbia-169 overlaps.
After all, peaks 110 and 118 keV belonging to
169Er also has a contaminant of 169 Yb, so in our sample they may not have even come from erbium-169 ..?..

The gamma spectrum of 169 Er consists mainly of relatively soft bremsstrahlung radiation with a continuous spectrum, which with a decreasing tendency stretches up to about 300keV. With longer acquisition, barely visible gamma peaks of 110 and 118 keV appear on this continuous background.
  From a spectrometric point of view, the radionuclide 169 Er itself is quite uninteresting and dull - only two very faint, barely visible gamma peaks of 110 and 118 keV can be seen against the continuous background of the braking radiation . However, what was our surprise when we had a sample of about 100kBq of erbium-169 preparation (citrate intended for radiation synovectomy of small joints) inserted into a sensitive gamma-spectrometer: after several tens of minutes of acquisition, the spectrum was literally "bristling" by a number of gamma-peaks, which, of course, did not belong to 169 Er, but to radionuclide impurities *) - see the picture above with accompanying text.
*) From the spectrum in the picture, it might seem at first glance that there are unbearably many of these radionuclide impurities..?.. However, it is just an "optical illusion"! Erbium-169 has a very low proportion of gamma radiation - only about every 20,000 transformations, one detectable 110keV gamma photon is emitted. However, those impurities such as ytterbium-169, samarium-153, ...., have many times higher gamma emissions (about 1000 times), so even their very small concentration (at the level of hundredth of %) will be more pronounced in the spectrum than alone 169 Er ..! ..
  The isotope 169 Er is prepared in a nuclear reactor by neutron irradiation of erbium oxide (enriched in the isotope 168 Er) by the reaction 168 Er (n, g ) 169 Er.
  Erbium-169 is used in the form of a colloidal solution of citrate in nuclear medicine for radiation synovectomy of small joints (fingers, wrists) - due to the low energy of emitted beta-particles, with a range in the tissue of about 1 mm.
Yterbium Yb 70 is also a soft silvery white metal from the lanthanide group. It is contained in the earth's crust in the form of compounds in a concentration of about 2.5-3 mg / kg. It has 7 stable isotopes: 168 Yb (0.13%), 170 Yb (3.04%), 171Yb (14.28%), 172 Yb (21.83%), 173 Yb (16.13%), 174 Yb (31.83%), 176 Yb (12.76%).
  Occasionally, one man-made radioisotope of ytterbium is used :
Ytterbium 169 Yb 
with a half-life of 32.02 days converted by electron capture (EC), a number of excited states of thulium
169 Tm: 316keV (5%), 379keV (82%), 473keV (13%); conversions to other higher excited states have a very low intensity (<0.01%) . In cascade deexcitation, many energies of gamma photons are emitted, of which the energies of 63, 110, 130, 177, 198 and 308 keV have a more significant intensity.


Conversion scheme and gamma spectrum of ytterbium
169 Yb. Apology: The semiconductor spectrum was measured on an older Ge (Li) detector with degraded properties.

The gamma spectrum of 169 Yb is dominated by the peaks of the characteristic X-ray Ka,b 49-59 kV, followed by the gamma peaks 63, 110, 130, 177, 198 and 308 keV. The peaks from the 139-> 118keV and 9.4-> 0keV transitions are weak because more than 99% are subject to internal conversion. A number of other higher peaks in the range of 316-781keV are so low (<0.01%) that in our weak sample (approx. 3kBq) they did not appear in the spectrum.
  The isotope
169 Yb is prepared in a cyclotron by irradiating thulia oxide with protons in a 169 Tm (p, n) 169 Yb reaction . ... and other reactions .....
  Yterbium-169 has been used in nuclear medicine for scintigraphic diagnostics , especially of the cerebrospinal fluid
(4.9.8, passage " Scintigraphy of cerebrospinal fluid pathways ") . 169 Yb is also being investigated as a potential radioisotope for brachytherapy (3.6, section " Brachyradiotherapy ") or defectoscopy (3.3, section " Radiation defectoscopy ") with a lower average gamma energy (93keV) than the commonly used iridium 192 Ir .
Terbium Tb 65 is another soft silvery shiny metal element from the lanthanide group. It is contained in the earth's crust in the form of compounds in a concentration of about 0.9 mg / kg. It was used in phosphors in screens and in X-ray intensifying films - it was printed by electronic development of digital imaging; it is now used as part of the recording layers of magneto-optical media.
  Terbium has one stable isotope of
159 Tb (100%). Of the radioactive isotopes of terbia, 149 Tb are tested experimentally in nuclear medicine :
Terbium 149 Tb
This artificially prepared radionuclide is transformed with a half-life by a very complex branched decay scheme with a half-life of 4.12 hours . In 76.2% electron capture occurs and in 7.1%
b+ -radioactivity takes place (mean Eb + = 730keV), in both cases to excited levels of 149 Gd. In 16.7%, alpha-radioactivity (Ea = 3.97MeV) reaches a baseline state of 145 Eu. During deexcitation of the excited states of daughter gadolinium-149, a large amount (more than 300!) of gamma-ray photons is emitted, of which photons with energy have significant intensity: 165keke (26%), 352keV (29%), 389keV (18%), 652keV (16%), 817keV (12%), 853keV (15%); high energy gamma peaks up to more than 3000keV are weak.


Conversion scheme and gamma spectrum of terbium 149 Tb ( .. The gamma-spectrum comes to be measured when I manage to obtain a sample of 149Tb ...) .
Due to the location, the complex decay scheme of 149 Tb is drawn in a simplified way, without details of poorly represented energy levels and transitions.

Both daughter radionuclides are again radioactive . The daughter gadolinium 149 Gd from the e - b+ branch is transformed by electron capture to a number of excited states of europium 149 Eu with energies mainly 150, 490, 790, 950 and 1083 keV, with subsequent emission of a number of gamma radiation lines. This europium 149 Eu is then again converted by electron capture by a half-life of 106 days into excited states of the already stable samarium 149 Sm. Daughter europium 145 Eu from alpha -branches with a half-life of 5.9 days are first converted by electron capture to excited states of samarium 145 Sm with emissions of a number of gamma lines, mainly with energies of 653, 893, and 1658 keV. This samarium is then again converted to 145 Pm with a half-life of 340 days by electron capture , which with a half-life of 17.7 years is also finally converted to a stable neodymium of 145 Nd by e-capture .
Preparation:
149 Tb is still a non-standard isotope and in small quantities it is experimentally prepared in three ways 1. Direct nuclear reactions with accelerated protons (energy approx. 100MeV) or helium nuclei: 149 Gd (p, 4n) 149 Tb, or 151,153 Eu ( 3, 4 He, x n) 149 Tb; 2. Reactions induced by accelerated heavier ions, eg nuclei 12 C: 141 Pr ( 12 C, 4n) 149 Tb, or 142 Nd ( 12 C, 5n) 149 Dy ( b+ , EC, T1/2 4min.) 149 Tb ; 3. Fragmentation reactions of high-energy protons, eg on a tantalum target: Ta (p, ..x ..) 149 Tb, with isotope separation.
  For nuclear medicine , 149 Tb terbium is interesting that it emits both alpha particles and beta+ positrons . In the chelating combination of 149 Tb with suitable target biomolecules, the same preparation (radiopharmaceutical) can be used both for diagnostic imaging of tumor lesions by positron emission tomography PET *) and for subsequent biologically targeted radionuclide therapy with use alpha-particles, with possible simultaneous PET monitoring of the course of therapy - ie for teragnostics (4.9, passage " Combination of diagnostics and therapy - teragnostics ") ; it is a " monoteranostic " radionuclide.
*) For gamma imaging, it is alternatively possible to use single-photon planar or SPECT scintigraphy using gamma radiation 165 or 352 keV, emitted during deexcitation of the daughter
149 Gd; due to the large amount of spurious high- g radiation, however, image quality is not good.
  The 149 Tb radionuclide has so far been experimentally tested in radioimmunotherapy of lymphoma for the designation of rituximab using DOTA or DTPA chelators, with preliminary promising scintigraphic and therapeutic results.
The problem of the teranostic use of
149 Tb can be a complex decay scheme, containing several daughter radioisotopes, some long - lived. Due to the relatively short half-life of 4.1 hours. is 149 Tb suitable for labeling lower molecular weight radiopharmaceuticals that are rapidly removed from the body. In this case, the potential radiotoxicity daughter radiolanthanid (converting the low load electron capture) did not significantly manifest. Due of its physical properties, terbium-149 would remain only as a curiosity, it will probably not certifies as teranostic radionuclide ...

Lutetium
Lutecium Lu
71 is a soft white shiny metal, the last member of the lanthanide group, which in the form of compounds is relatively rare in nature (0.5-0.7 mg /kg in the earth's crust). It is used in LSO scintillation detectors for positron emission tomography (2.4., Part " Scintillators and their properties ", 4.3, part " PET cameras ") . It has the only stable isotope 175 Lu (97.4%), while natural lutetium also contains 2.6% of the isotope 176 Lu, which is radioactive :
Lutetium 176 Lu
is a natural (primordial) radionuclide which, with a very long half-life of 3.76.10
10 years b- -radioactivity, is converted to stable hafnium 176 Hf - to an excited state of 597 kV. Deexcitation occurs by gradual (cascade) emission of gamma photons with energies of 307, 202 and 88keV (a higher energy of 401keV is weakly represented, a weak summation peak 306 + 202keV also appears in the spectrum) . It is used for long-term dating in nuclear geochronology using the lutetium-hafnium method (see " Radioisotope dating " above) . The content of natural 176 Lu has a somewhat adverse effect on "internal contamination" LSO scintillators and their relatively high radiation background (see 2.4 "Scintillators and their properties " and 4.3 " PET cameras ") .


Conversion scheme and gamma spectrum of lutetium
176 Lu

Lutetium 177 Lu
is an artificially produced radionuclide, which with a half-life of 6.65 days is converted by beta
- -radioactivity (Eb max = 498keV) to 177 Hf - from 79.4% to the ground state, further to excited states 113keV (9%) and 321keV (11.6%). During the deexcitation of excited 177-hafnium nuclei, photons of gamma radiation with energies mainly 113keV (6.2%) and 208keV (10.4%) are emitted , with low intensity (approx. 0.2%) then 72, 250 and 321 keV. At the beginning of the spectrum, the peak of characteristic X-radiation (Ka,b Hf) 55-63 keV is visible.


Conversion scheme and gamma spectrum of lutetium 177 Lu.
For the sake of interest, a simplified decay scheme of the metastable isomer
177m Lu, which often forms together with 177 Lu, is also drawn in the upper left left .

The 177Lu isotope is produced by irradiating neutrons in a nuclear reactor in two ways:
- The direct method consists in irradiating lutetium enriched in the 176 Lu isotope with neutrons in the 176 Lu (n, g ) 177 Lu reaction . Due to the high effective cross section of this reaction, a radionuclide with a relatively high specific activity can be obtained. A certain disadvantage of this process is the ongoing reaction of 176 Lu (n, g ) 177mLu, which produces the nuclear isomer 177mLu with a half-life of 160 days. This unwelcome contaminant is dexcited in 22% by gradual isomeric transitions to the ground state of 177 Lu and in 88% is converted separately b- -radioactivity (Eb max = 153keV) to a relatively high excited state of 1315keV of the daughter 177 Hf, which deexcites through a series of g- transitions towards lower levels. At this radioactivity, 177mLu emits a number of gamma energies, some of which are the same as for 177 Lu, but higher energies of 228, 281, 319, 378, 418 keV and many others are also represented. Contaminant radiation 177mLu increases the radiation exposure and deteriorates the quality of scintigraphic images for a long time.
- Indirect method consisting in the combination of neutron irradiation of ytterbium, enriched in the isotope
176 Yb, neutrons in the reaction 176 Yb (n,g ) 177 Yb and subsequent beta-conversions of 177 Yb ( b- , T1/2 = 1.9 hours) 177 Lu to the resulting lutetium-177. This method does not produce interfering 177mLu (with the beta-conversion of 177 Yb, the metastable level of 970keV 177mLu is not saturated ) , only trace amounts of Yb isotopes may be present....

Gamma spectrum of a 3 month old sample 177 Lu (Betalutin preparation) .
Apology:
During the graphic processing of the spectra, the scales on the horizontal axis were deformed. However, the numerical values of the energies above the peaks are accurate.

Lutetium-177 is used in nuclear medicine for biologically targeted radioisotope therapy of cancer (3.6, section " Radioisotope therapy ") . There is marginal use in the form of 177Lu-EDTMP for the palliative therapy of bone metastases (since strontium 89 Sr, samaruim 153 Sm and rhenium 186 Re have been tested for this purpose ) . More common is the therapy of neuroendocrine tumors using a conjugate of chelate 177Lu-DOTA with the peptide octreotide , which binds to neuroendocrine tumor cells with a sufficiently high concentration somatostatin receptors . However, very good results are shown in particular by 177Lu- labeled monoclonal antibodies , such as 177Lu-J591 anti-prostate specific membrane antigen (PSMA) or 177Lu-tetulomab anti-CD-37 for the treatment of lymphomas.
  These methods are described in 3.6, section "
Radioimmunotherapy ".
  Beta radiation with a mean energy of 134keV has a therapeutic effect . The advantage of 177 Lu is that gamma emission allows simultaneous scintigraphic imaging in therapy tissues and organs into which the therapeutic preparation has penetrated. On these scintigraphic images we can assess (visually, or even quantitatively) the degree of desirable uptake of radiopharmaceuticals in tumor foci and unwanted accumulation in healthy tissues and critical organs - to monitoring the course of radioisotope therapy . The representation of gamma radiation also allows easy measurement of the activity of 177 Lu preparations in conventional ionization chamber activity meters (2.3 " Ionization chambers ") , using the appropriate gamma-constant calibration.

Tungsten, Rhenium
Tungsten (wolfram) W 74 is a gray-white shiny, heavy (density 19.25 g /cm3 ) and difficult-to-melt metal (melting point 3422 C). It is relatively rare in nature (approx. 1.5-3.5 mg /kg in the earth's crust), in compounds (ores - oxides) together with iron, manganese, calcium or lead. Tungsten has a wide technical application due to its high density and heat resistance. For high melting points, it is used as a material for filaments in light bulbs and tube cathodes (including electron sources in accelerators). Tungsten alloys are used in metallurgy to increase the hardness , mechanical and thermal resistance of metals. Due to its high density, it is used as effective radiation shielding of X-ray and gamma radiation (1.6, section " Radiation absorption in substances ", section " Gamma radiation shielding ") , for the production of containers and precision collimators.
  It has 5 stable isotopes:
180 W (0.12%), 182 W (26.5%), 183 W (14.31%), 184 W (30.64%), 186 W (28.43%).
Note:
The
180W isotope was found to have very weak radioactivity - alpha-conversion to hafnium 176 Hf with a hugely long half-life of 1.8.1018 years. It is suspected that other natural isotopes of tungsten are perhaps in the long run a-radioactive (converted to the corresponding hafnium isotopes), with even longer half-lives. It is very difficult to verify (in a sample of 1 gram of tungsten it would represent less than one alpha-conversion per year) .
  Of the radioactive isotopes of tungsten, only one is worth mentioning here :
Tungsten 188 W
With a half-life of 69.4 days, is converted by
b- -radioactivity from 99% to the ground state of rhenium 188 Re, from 1% to several excited levels, during which deexcitation emits several photons of gamma radiation, especially with energies of 227 and 290 keV. The 188 W isotope is prepared by neutron irradiation of metallic tungsten (enriched to about 95% with the isotope 186W) in a nuclear reactor by double neutron capture: 186 W (n, g ) 187 W (n, g ) 188 W. It serves as the parent isotope in the 188W / 188Re generator to obtain the 188 Re radionuclide in nuclear medicine (see Re-188 below).

Rhenium Re 75 is also a very heavy, hard and difficult-to-melt metal, very rarely present in nature (approximately 1-5 ng /kg in the earth's crust) . Natural rhenium is a mixture of 37.4% of the stable isotope 185 Re and 62.6% of the radioactive isotope 187 Re ( b- , half-life 4.33.1010 years). Three radioactive isotopes of rhenium are of practical importance :
Rhenium 187 Re
is a natural (primordial) radionuclide, which with a very long half-life of 4.33.10
10 years by b- -radioactivity is converted to the basic state of osmium 187 Os. It is used in long-term radiosotope dating - nuclear geochronology - for determining the age of rocks by the 187Re / 187Os method (see " Radiometric dating " above) . 
Rhenium 186 Re
is an artificially produced radionuclide which, with a half-life of 3.72 days, is branched transform in 92.53% by beta
- -radioactivity to 186 Os and in 7.47% by electron capture to 186 W. b- transformations take place in 71% to the ground state (E b max = 1070keV) and in 21.5% to excited levels of 186 Os with energy 137keV (in a small fraction of a percentage also to higher excited levels) . Electron capture takes place in 5.8% to the ground state and in 1.7% to the excited state 122keV 186 W. During deexcitation g photons are emitted radiation mainly with energy 137keV (9.4%) and 122keV (0.6%).
  The isotope
186 Re is obtained by neutron irradiation of rhenium (preferably enriched in the isotope 185 Re) in a nuclear reactor by the reaction 185 Re (n, g ) 186 Re, or in a cyclotron by proton irradiation of tungsten (highly enriched in the isotope 186 W) in a reaction of 186 W (p, n) 186 Re.
  Rhenium-186 is used in nuclear medicine in the form of a phosphonate complex for the palliative therapy of bone metastases
(3.6, part " Radioisotope therapy ", passage "Radionuclide therapy of tumors and metastases ") and in the form of colloidal sulphite for radiation synovectomy in rheumatoid arthritis of medium - sized joints (wrist, elbow, shoulder) - 3.6, passage" Radionuclide synovectomy " .


Decomposition scheme and gamma spectrum of rhenium
186 Re.

Rhenium 188 Re
is also an artificially produced radionuclide, which with a half-life of 16.98 hours is converted by
b- -radioactivity (Eb max = 2115keV) to 188 Os - from 70.6% to the ground state, from 26% to an excited level of 155keV, during the subsequent deexcitation, gamma radiation of the same energy is emitted. With low representation, beta-transformations also take place in other excited states of 188 Os, whose radiation has a very low intensity.
  The
188 Re isotope is most often obtained by elution from a 188W / 188Re generator (mentioned above), or is prepared by neutron irradiation of rhenium (highly enriched in the isotope 187Re) in a nuclear reactor: 187 Re (n, g ) 188 Re. It has been used in recent years in nuclear medicine for similar applications to the above-mentioned more common 186 Re (advantage of 188Re is easier preparation from the generator, higher specific activity, shorter half-life and higher energy of beta particles) .

Iridium
The heavy noble metal iridium Ir
77 is rarely present in nature (approximately 0.001 mg /kg in the earth's crust) with its two stable isotopes 191 Ir (29.5%) and 193 Ir (62.7%). It has a high density (22.6 g /cm3 ) and is very chemically resistant *). Along with platinum, it is used in metallurgy and a number of technical applications.
*) Known standards of meters and kilograms were made of an alloy of platinum and iridium at the International Institute of Weights and Measures in Sevres, near Paris.
Iridium 192 Ir
A heavy radionuclide often used as a gamma emitter is iridium 192 Ir . With a half-life of T1/2 = 74.2 days, it decays from 95.1% b- -radioactivity to excited platinum levels of 192 Pt and from 4.9% electron capture to excited osmium levels of 192 Os. At this radioactivity of 192 Ir, it emits a number of deexcitation lines of gamma radiation in the range of 130-1380keV with significant peaks 296keV (29%), 308 (30%), 316keV (83%), 468 (48%) and 604+613keV (8.2%). Several other very faint gamma lines of higher energies are visible in the spectrum only at high magnification. Conversely, at the beginning of the spectrum, the lines Ka,b of the characteristic X-rays of osmium and platinum 61-78 keV are visible , arising from deexcitation transitions in the envelope of these daughter atoms after electron capture of the electron from the K shell and after internal conversion of gamma radiation.   Iridium-192 is used as an intense source of gamma radiation with medium energy in defectoscopy (3.3, part " Radiation defectoscopy ") and in brachytherapy (3.6, part " Brachyradiotherapy "). These high activity emitters (GBq-TBq) are prepared by a nuclear reaction of 191Ir (n, g ) 192Ir by irradiating metallic iridium (wires, plates, pellets) with neutrons in a nuclear reactor.


Conversion scheme and gamma spectrum of iridium 192 Ir

Thalium
Thalium Tl
81 is a soft white shiny metal from group III.B, which occurs in nature only in compounds and relatively rarely (approximately 0.05-2 mg /kg in the earth's crust). It has two stable isotopes, 203 Tl (29.5%) and 205 Tl (70.5%). Of the radioactive isotopes of thallium, it is worth mentioning the natural 208 Tl (as a decay product of thorium-232) and especially the artificially produced 201 Tl :
Thalium 201 Tl
is an artificially produced radionuclide, which with a half-life of 3 days is converted by electron capture EC to
201 Hg. From 21% it is to the baseline state, in 41% to the excited level of 167keV and in 13% to the level of 32keV. During deexcitation, gamma photons with energies of 135keV (2.6%) and 167keV (10%) are emitted. However, the main component of the photon radiation 201 Tl is the characteristic X-rays of mercury, arising during the transitions of electrons in the envelope after K-capture: Ka 68-71keV (73.7%) and Kb 79-83keV (20.3%) , soft X radiation of 8-15keV (43%) is of less importance. As with any EC radionuclide, in the radiation of 201 Tl are significantly present Auger electrons , mainly with energies of 53-58keV (100%), 64-68keV (55%), 75-83keV (7.6%), also low-energy electrons 5-15keV (> 50%).
   The isotope
thallium-201 is prepared by irradiating natural thallium (or enriched in the isotope 203 Tl) with protons in a cyclotron by a nuclear reaction of 203 Tl (p, 3n) 201 Pb, followed by radioactive conversion of 201 Pb with a half-life of 9.4 hours by electron capture on the resulting 201 Tl (an alternative option for the preparation of intermediate 201 Pb is the reaction 205 Tl (p, 5n) 201 Pb ).
Note:
It is difficult to obtain absolutely pur e
201 Tl by these reactions - depending on the energy of the irradiating protons, one or more neutrons are often ejected. In most cases, therefore, the preparation also contains radionuclide impurities of neighboring thallium isotopes 200,202Tl - see the lower part of the figure of the 201-Tl spectrum.
  Radionuclide 201 Tl in the form of chloride is used in nuclear medicine for scintigraphy of myocardial perfusion *), as an analogue of potassium, in a one-day protocol - 4.9.4 " SPECT myocardial perfusion ". 201T1 cations accumulate in cardiac muscle cells similarly to potassium ions. After application of radio indicator 201T1, areas of cardiac muscle with reduced blood flow are displayed on the scintigram as hypoactive areas .
*)
201 Tl was widely used especially in the 80s-90s. years. Its disadvantage is the low energy of the dominant X-rays, which causes poorer resolution and significant absorption in the tissue; also a considerable radiation load (to which significantly represented Auger electrons also contribute) . Thalium has now been extruded by 99mTc- labeled isonitriles, with which much higher quality images are obtained with a significantly lower radiation exposure. In the near future, however, one may expect a partial "renaissance" of thallium in connection with the introduction of semiconductor CZT cameras (4.2., Part "Alternative physical principles of scintillation cameras ", passage" Semiconductor cameras ") , which have a higher sensitivity for photon X radiation 73keV 201Tl.


Conversion scheme and gamma spectrum of thallium
201 Tl.   Above: Pure thallium-201.
Bottom:
201-thallium prepared in a cyclotron by a nuclear reaction
[
203Tl(p,3n)201Pb; 201Pb(EC,T1/2=9,3hour)201Tl]
often contains about 0.1% of radionuclide impurities
200,202Tl .
In the gamma spectrum of such a preparation, in addition to the basic peaks of
201Tl, weaker peaks with higher energies are visible after magnification:
367,579,828,1205 keV from the
200Tl contaminant and peaks of 439, 520 keV from 202Tl.

Lead, Bismuth
The heavy metals lead and bismuth are the last elements of Mendeleev's periodic table that still have stable isotopes
(bismuth is only a "practically" stable isotope, see below) . They are also end members of the radioactive decay series of thorium, uranium and transuranes (see " natural radionuclides " above) .
Lead Pb 82 ( Plumbum ) is a soft low-melting metal (melting point 327.5 C) , which is relatively rare in nature (approx. 0.05-2 mg /kg in the earth 's crust) *). It is mostly found in compounds such as lead sulphide (galenit), lead sulphate and lead carbonate. It is classically used in the production of batteries, lead glass, ammunition. In the field of radiation physics, its high density and absorption capacity for X and gamma radiation is important - it is used as an effective shielding material (1.6, section " Absorption of radiation in substances ", passage " Shielding of ionizing radiation ") .
*) However, the lead content is still slightly higher than, according to cosmic nucleogenesis, would correspond to its high proton number. This is because lead isotopes are the end product of the radioactive decay series of uranium and thorium (see Fig.1.4.1 ), so that over the course of billions of years, the lead content in the earth's crust gradually increased .
  Lead has 4 stable isotopes: 204 Pb (9.4%), 206 Pb (24.1%), 207 Pb (22.1%), 208 Pb (15.4%). From the radioactive isotopes of lead worth mentioning mainly three :
Lead 210 Pb
with a half-life of 22.3 years converts beta
- -radioactivity to 210 Bi - 20% in the basic state, in 80% of the excited state 46.5keV. Max. beta energy is relatively low, 63keV. In nature, it is constantly emerging as one of the products of gradual transformation 238U in the uranium decay series (Fig ....). In closed uranium-containing materials, such as rocks, the 210 Pb isotope is in permanent radioactive equilibrium with 238 U and its daughter isotopes. ....
Lead 214 Pb
with a half-life of 26.9min. converts by beta
- -radioactivity to 214 Bi, mainly to excited levels of 295 and 362 keV, during the deexcitation of which gamma radiation with energies of 352, 195 and 242 keV is emitted - see below the spectrum of Radium 226 Ra . Like 214Bi in nature is constantly formed as one of the products in the uranium decay series (Fig ....). In closed materials containing uranium, such as rocks, the isotope 214 Pb is in permanent radioactive equilibrium with 238 U and its daughter isotopes. ........
Bismuth Bi 83 ( Bismuthum ) , also called vismuth , is a shiny silvery pinkish crystalline low-melting metal (melting point 271 C) , rarely present in nature (approx. 0.2 mg /kg in the earth's crust), as corresponds to its high proton number. It is used for the preparation of low-melting alloys such as Wood's metal (50% Bi, 25% Bb, 12.5% Sn, 12.5% Cd), which has a melting point of 60.5 C. Due to its high density and absorption capacity for X-rays, Bi is sometimes used in X-ray diagnostics in shielding veils for radiation protection.
  Natural bismuth is formed by the isotope
209 Bi , which was until recently considered stable. In 2003, however, it was found that this isotope is weakly radioactive - with an extremely long half-life of 1.9.1019 years, it is subject to alpha-radioactivity. From a practical point of view, however, natural bismuth appears to be non-radioactive (300 kg of bismuth would have an activity of 1Bq) , with radiation deep beneath the natural background. Of the (really) radioactive isotopes of bismuth, three natural and two artificial radionuclides are partly important :  
Bismuth 212 Bi
occurs in nature as one of the products of the thorium decay series (....). With a half-life of 60.5min. from 36% converted by
a-radioactivity to 208 Tl and 64% by b- -radioactivity to 212Po. ...........
Bismuth 213 Bi
is converted from 97.8% by
b --radioactivity to 213 Po and from 2.2% by a-radioactivity at 209 Tl ..........
  Isotopes
214,213Bi are experimentally used in nuclear medicine for radioimmunotherapy (3.6, part " Radioisotope therapy " passage" Radioimmunotherapy ").
Bismuth 214 Bi
is one of the ephemeral but important products of decay series of uranium (...). The relatively short half-life 19.8 minutes was converted by a complex decay scheme mainly beta
- -radioactivity in a number of excited level and the ground state of polonium 214 Po, slight extent (0.021%) also alpha radioactivity to excited levels 210 Tl. When deexcitation (especially levels 214 Po) a number of gamma radiation energies are emitted, of which 609.3 keV (45.5%), 665 (1.5%), 768 (4.5%), 1120 ..... have a significant share - see figure Ra -226 left .
  Significant gamma-lines
214 Bi can be observed in uranium and radium (if it is in equilibrium with its daughter nuclides - see below Radium 226 Ra ) and also in most natural samples, where this radionuclide enters with radon gas (see, for example, the above figure .1.4.2 ) .

Thorium, Uranium, Radium, Actinium, Radon
Heavy nuclei uranium groups which are all
a -radioactive are particularly important following nature (primary) radionuclides of thorium and uranium:
Thorium Th 90 is a silvery white metal that is quite abundant mineral compounds represented in the earth's crust (9.6 mg /kg). It has no stable isotope, in terrestrial nature it occurs mainly weakly radioactive thorium-232 :
Thorium
232 Th
Thorium
232 Th 90 is one of the most widespread natural radionuclides contained in the rocks of the earth's crust (along with 40K) , its content is about 9 mg/kg. With a very long half-life T1/2 = 14,02.109 years, it decays by alpha-radioactivity to radium 228 Ra and then by the whole decay series according to the left part of Fig.1.4.1 . It does not yet have direct radiation use, but in the future it may be a potential fissile material in thorium-uranium cycle in propagation nuclear reactors - 1.3, part " Fast FBR propagation reactors " . Due to the low specific activity and the impossibility of use for direct chain fission, thorium-232 can be considered as an almost non-radioactive material from the point of view of nuclear physics and radiation protection, with neglible (or zero) risk.
  Thorium can be used as a material for effective shielding of ionizing radiation. Furthermore, 232 Th is sometimes used in technical practice as an additive to lamp electrodes , where ionization of the gas charge by alpha particles facilitates the ignition of an electric discharge at a lower voltage (3.7, passage " Radioactivity in lamps ") . Another use of thorium (230-Th) is in uranium-thorium radiometric dating (see " Radiometric dating " above) .
Thorium 227 Th
is an artificially produced radioisotope for use in biologically targeted radionuclide therapy . With a half-life of T
1/2 = 18.7 days , alpha-radioactivity is converted to radium 223 Ra - in 25% to baseline, 24% to 61.5keV, 20% to 286keV, 5% to 329keV, in 8% to 334kev, with a lower representation on a number of other excited states. During deexcitation, a number of gamma photons are emitted, mainly energies of 50keV (8%), 236keV (12.4%) and 256keV (7%), weaker are 300keV (2.3%) and 330keV (2.7%). The energies of alpha-particles range from 5.7-6 MeV, depending on the excited levels. The daughter 223 Ra is then again a-radioactivive with a half-life of 11.4 days converts to radon-219 and further through the whole decay chain of short-term isotopes to stable lead-207 (cf. the picture below in the passage " Radium 223 Ra ") , with the emission of many other energies of alpha particles, beta electrons and gamma photons :

  As is typical for heavy uranium nuclides (and higher), even 227 Th is converted by a whole decay series : 227 Th (18.7d .; a ) 223 Ra (11.4d .; a ) 219 Rn (4s .; a ) 215 Po (1.8ms .; a ) 211 Pb (36.1min .; b - ) 211 Bi (2.2min .; a ) 207 Tl
  (4.8min .; b - ) 207 Pb (stable).
During the first conversion of
227 Th (to 223 Ra radium ) , alpha radiation with energies of 5.7-6 MeV and gamma radiation with energies of mainly 50, 236 and 256 keV are emitted.
When the radioactivity of daughter nuclides decay chain is emitted, then a number of other energy alpha particles, beta and gamma photons, in particular: from
223Ra it's a 5.6 5,7MeV and gamma rays with energies of 154 and especially 269 keV; of 219Rn is it a 6.4 and 6.8 MeV and g 271 and 402 keV; of 215Po it and 7,4MeV; of 211 Pb it is beta 540 and 1372 keV and weak g 404 and 832 keV; from 211Bi it is a 6.3 and 6.6 MeV and g 351keV; of 207Tl , beta max. energy 1423keV and weak gamma 898keV are emitted.
Secondary branch
211 Bi ( b - ) 211Po due to its low proportion (0.27%), it has no practical significance.
  The 227-Th decay chain functions as an " in vivo radionuclide generator " - see " In vivo generators " above.
A simplified conversion scheme of
227Th to 223Ra is drawn below in the left part of the figure.
The measured spectrum of gamma radiation emitted by all nuclides from the entire 227-Th decay series is shown below in the right part of the figure.
e 
Conversion scheme of 227 Th thorium (first conversion to radium-223) and the total gamma spectrum of 227 Th and its decay products.
The spectrum was measured with a hermetically sealed preparation from which 219 Rn radon gas could not escape . The spectrum therefore contains gamma lines and all daughter radionuclides of the decay series, with which 227 Th is in radioactive equilibrium. The gamma lines derived from the conversion of 227-Th to 213-Ra are given in the spectrum without labeling (only with energy value), for photopeaks from secondary transformations in the decay series, the corresponding radionuclides from which they originate are listed (especially 223Ra, 219 Rn, 211 Bi, 211 Pb and 207 Tl).

One complete radioactive transformation of the 227 Th nucleus in the entire decay series to a stable 207 Pb releases a total nuclear energy Q = 36.132 MeV , which is carried away by about 95% by five alpha particles , by 3% by beta + neutrons and by about 1% gamma photons and X-rays. For thorium 227 Th and daughter products of the decay series, mainly emitted alpha radiation with energies of 5.4-7.4 MeV (a total of 5 alpha particles / 1 conversion of 227 Th ) is used in nuclear medicine for biologically targeted radionuclide therapy.
  Gamma radiation of 227 Th and its daughter nuclides are practically does not manifest in therapy, but can be used for gammagraphic monitoring of the distribution of radiopharmaceuticals in the body. Emission of gamma radiation during therapy allows simultaneous scintigraphic imaging of tissues and organs into which the therapeutic preparation has penetrated. On these scintigraphic images we can assess (visually, or even quantitatively) the degree of desirable uptake of radiopharmaceuticals in tumor foci and unwanted accumulation in healthy tissues and critical organs - to monitor the course of radioisotope therapy .
  Chemical properties of thorium (oxidation state +4) they allow, with the help of a macrocyclic ligand of the DOTA type, chelating binding of 227Th to monoclonal antibodies to form radioimmunoconjugates that are specifically taken up in tumor cells (the structure and properties of monoclonal antibodies are discussed in more detail in 3.6, section " Targeted biological therapy - monoclonal antibodies ") . High energy a particles capable emitted during radioactive transformations, they can effectively destroy the tumor cells. In the laboratory trial phase, targeted immunotherapy using alpha- labeled thorium monoclonal antibodies is in lymphomas 227Th-rituximab or anti-CD22, in acute myeloid leukemia 227Th-conjugate CD33 lintuzumab.
  A certain problem may be the release of daughter radium-223 from the chemical bond in the radioimmunoconjugate due to the backscattering of the nucleus during alpha-particle emission
(1.2, passage " Backscattering of the nuclei ") and differences in the chemical properties of the radium (oxidation number 2). If daughter radium escapes from the target tissue during its transformation (T1/2 = 11.4 days) , the effectiveness of the therapy is reduced by 4 energetic alpha-particles from the radium-223 decay series. The released 223 Ra can then be taken up in other tissues (eg bones) and cause unwanted radiation exposure there.
  Preparation: Isotope 227 Th is artificially prepared by irradiating radium-226 with neutrons to form radium-227: 226 Ra (n, g ) 227 Ra, followed by conversion by beta-- radioactivity 227 Ra ( b- , T1/2 = 41min.) 227 Ac to actinium-227, which with a half-life of 21.8 years is converted to the resulting thorium-227: 227 Ac ( b- , T1/2 = 21.8y.) 227 Th. Due to the long half-life of actinium-227, 227Th can be continuously obtained by elution from a 227Ac / 227Th generator .
 Uranium U 92 is a very heavy (19g / cm 3 ) metallic element of silver-white color from the group of actiniodes. It acquires a dark gray color in air due to oxidation. It was isolated in 1841 and named after the then newly discovered planet Uranus . It was used to color glass. In 1896, H.Beckerel discovered previously unknown penetrating radiation in uranium-containing minerals - he discovered radioactivity (1.2 " Radioactivity ") . Uranium has no stable isotope, all 28 known isotopes are radioactive . The natural metallic element uranium U 92 consists mainly of the isotopes 235 U (0.7204%) and 238 U (99.2742%), which are important natural primordial radionuclides ; there is also a trace amount of 234 U (0.0054%), which is formed as a secondary intermediate of the decay series 238 U.
Uranium
 
235 U
decays with alpha-radioactivity to thorium
231 Th with a long half-life T1/2 = 7.04.108 years and then the whole decay series according to the middle part of Fig.1.4.1 . By absorbing the neutron, the 235U nucleus splits into two lighter nuclei. Uranium-235 is the basic fissile material in nuclear reactors, the fission of which generates a large amount of energy in nuclear power plants; nuclear reactors also serve as a powerful source of neutrons for many applications of nuclear physics and chemistry. For details, see 1.3 " Nuclear reactions ", section " Fission of atomic nuclei ".
Uranium 238 U
with a very long half-life T
1/2 = 4.47.109 years decays by alpha-radioactivity to thorium 234 Th and then by the whole decay series according to the right part of Fig.1.4.1 . Due to its longer half, it is 238U the most common type of uranium in nature. It can also be used as fissile material, but not directly, but via plutonium , which is formed in the nuclear reactor from 238 U by neutron absorption (1.3, section " Fast FBR propagation reactors ") . Uranium-238 (as so-called " depleted uranium ") has only relatively low radioactivity (see the table in the section " Relationship between half-life and activity " 1.2 " Radioactivity ") and is sometimes used as an effective shielding material for high-energy gamma radiation.
  Uranium's own alpha-radioactivity produces relatively little gamma radiation. In g-specrum, we can see from uranium only not very significant lines 185keV and 205keV from the conversion of 235 U to metastable levels 231 Th. Most gamma-radiation of uranium comes from daughter radionuclides of the decay series, mainly from thorium 234 Th (63keV, 93keV), then from radium-226 (185keV) and mainly from lead 214 Pb and bismuth 214 Bi (214, 295, 352, 609 keV and many others ...).


Simplified conversion scheme of uranium
235 U and 238 U and gamma spectrum of natural uranium and some of its decay products.
The gamma spectrum was measured from a sample of loose 0.3 mm thick uranium metal sheet. A series of daughter radionuclides in the decay series was interrupted here for radon 219.222Rn, which, due to its gaseous state, escapes smoothly from the sample. Therefore, there are no gamma lines in the spectrum of other radionuclides of the decay series, eg 214 Pb and 214 Bi, which can be seen, for example, in the spectrum of a sample of encapsulated radium (see " Ra-226.gif " below), or in samples of the natural environment (e.g. " NaturalRadioactivity.gif ").

Uranium 234 U
decays with a half-life T
1/2 = 245.5 thousand years by alpha-radioactivity to thorium 230 Th and then by a 238-uranium decay series to lead-206. It is formed in small quantities as part of the 238 U decay series . It has no practical significance, it is not a fissile material. The last somewhat technically significant isotope of uranium is man-made :
Uranium
233 U ,
which decays with alpha-radioactivity to thorium 229 Th with a half-life of T1/2 = 159.2 thousand years (and then a neptunium decay series to Bi-209 - shown below in the passage " Actinium 225 Ac ", in the picture on the top left). Uranium-233 is formed from thorium 232Th by neutron absorption in the reaction 232Th90(n,g)233Th90(b-;12min)233Pa91(b-;27 days)233U92. Uranium 233U can potentially serve as fissile material in thorium fuel cycle reactors (Fast Propagation Reactors FBR) .
  The decay products of thorium and uranium are a number of other radioisotopes (they form the so-called decay series described above, Fig . 1.4.1 ) , the most important of which is radium :
Radium Ra 88
is an important radioactive element associated with the history of radioactivity in the early 20th century. Radium is a silvery-white, heavy and highly reactive alkaline earth metal. All its isotopes are radioactive . In nature, four isotopes of radium occur in trace amounts:
223 Ra (T1/2 = 11.4 d.), 224 Ra (T1/2 = 3.64 d.), 226 Ra (T1/2= 1602 years), 228 Ra (T1/2 = 5.75 years). They come from the decay series of uranium and thorium. Radium isotopes with alpha-radioactivity are converted to the corresponding radon gas isotopes and then through a whole 5-6 member decay series to a stable lead isotope (with the exception of 228Ra in the thorium series, which is converted by a 10-membered series comprising radium-224 and radon-220) .
Radium 226 Ra
The most important isotope of radium is
226 Ra , discovered and isolated from uranium ore in 1898 by M. and P. Curie. 1 gram of 226 Ra, isolated by the heroic efforts of Mrs. M. Curie and their collaborators, served for a long time as a standard of the former unit of activity 1 Curie (1Ci). With a half-life of T1/2 = 1602 years, 226-radium is converted by alpha-radioactivity to radon 222 Rn (and then by a whole decay series to a stable lead of 206 Pb) . In 94.4% takes place a conversion to the basic state of radon, 5.5% in the excited state
186keV , three other higher excited levels are underrepresented.
  226 Ra itself is a mixed a + g emitter (E a = 4.78MeV, E g = 186keV) , but in reality it is in equilibrium with its daughter isotopes in the decay series. In the spectrum of gamma radiation 226 Ra we see our own peak 186keV, but the lines of daughter products 214 Pb and 214 Bi are much more pronounced (with higher energies: 295, 352, 609, 768, 1120, 1238, 1378, 1764, 2204, 2448 keV) . Radiophores 226 Ra were previously used in brachyradiotherapy (3.6, part " Brachyradiotherapy") , are now extruded mainly by iridium-192 (see" Iridium "above) .


Conversion scheme of
226 Ra radium and gamma spectrum of 226 Ra and its decay products. In the section in the left part of the figure there are simplified decay schemes of important radionuclides 214 Pb and 214 Bi from the decay series radium-226.
The spectrum was measured with an encapsulated 226 Ra standard from which 222 Rn radon gas could not escape , so that 226 Ra is in radioactive equilibrium with its daughter products. Therefore, in the spectrum (in contrast to the above-mentioned uranium spectrum), the gamma lines of all daughter radionuclides of the decay series, especially 214 Pb and 214 Bi, are shown.

Radium 223 Ra
is unlike previous natural nuclides artificially produced radioisotope for radionuclide therapy in nuclear medicine
(naturally isotope 223 Ra present in very small quantities as one of the decay products of uranium 235 U in the uranium-actinium decay chain - obr.1.4 .1 ) . 223-radium is converted by alpha-radioactivity *) with a half-life of 11.43 days to radon 219 Rn (and then by a decay series to stable lead 207 Pb, see below). Only 1% is converted to the ground state, in most cases it is a series of excited states 219 Rn. The most represented are conversions to levels with energies of 127keV (9.5%), 154keV (52.5%), 269keV (24.2%), 338keV (9.2%), during the deexcitation of which gamma radiation is emitted (the largest proportion here they have energies of 154 and 269keV, the weaker is 324keV) . Alpha radiation from 223 Ra conversion has energies in the range of 5.5-5.7MeV. Additional energies alpha, beta and gamma are emitted from the daughter products of the decay series, see below - cf. also the picture above in the passage " Thorium 227 Th " .
*) A little interest :
223Ra was the first isotope for which a new radioactive transformation was discovered in 1984 with the emission of particles heavier than alpha-particles - " carbon radioactivity " with the emission of nuclear 14 C: 223 Ra 209 Pb + 14 C (see 1.2, part " exotic species of radioactivity , " passage " radioactivity higher than a -helium "). However, this process is very weak, at the limits of measurability, the ratio of the number of emissions of 14 C and alpha emissions (ie 4 He) is 6.4.10-10 .
  Preparation: Isotope 223 Ra is artificially prepared by irradiating radium-226 with neutrons to form radium-227: 226 Ra (n, g ) 227 Ra, followed by conversion by beta --radioactivity 227 Ra ( b- , T1/2 = 41min.) 227 Ac to actinium-227, which with a half-life of 21.8 years is converted via thorium-227 to the resulting radium-223: 227 Ac ( b- , T1/2 = 21,8r.) 227 Th ( a , T1/2 = 18,7d.) 223 Ra. Due to the long half-life of actinium-227, 223Ra can be continuously obtained by elution from a 227Ac / 223Ra generator (selective elution is performed with a solution of about 0.1 mol. HCl or HNO 3 ) .

  As is typical for heavy uranium nuclides (and higher), even 223 Ra is transformed by the whole decay series :
223 Ra (11.4d .; a ) 219 Rn (4s .; a ) 215 Po (1.8ms .; a ) 211 Pb (36.1 min .; b - ) 211 Bi (2.2 min; a ) 207 Tl (4.8 min; b - ) 207 Pb (stab.).
  During the first conversion of 223 Ra (to radon 219 Rn), alpha radiation with energies of 5.6 and 5.7 MeV and gamma radiation with energies of especially 154 and 269 keV are emitted.
  During the radioactivity of the daughter nuclides of the decay series, a number of other energies of alpha, beta and gamma photons are emitted, in particular: from 219Rn it is a 6.4 and 6.8 MeV and g271 and 402 keV; of 215Po it is a 7,4MeV; of 211Pb it is beta 540 and 1372 keV and weak g 404 and 832 keV; from 211 Bi it is a 6.3 and 6.6 MeV and g 351keV; of 207 Tl , beta max. energy 1423keV and weak gamma 898keV are emitted.
  Secondary branch 211 Bi ( b - ) 211 Po due to its low proportion (0.27%) has no practical significance.
  The 223-Ra decay chain functions as an " in vivo radionuclide generator " - see " In vivo generators " above.
  The measured spectrum of gamma radiation emitted by all nuclides from the entire 223-Ra decay series is shown below in the right part of the figure. e
Conversion scheme of 223 Ra radium (first conversion to radon-219) and the total gamma spectrum of 223 Ra and its decay products.
The spectrum was measured with a hermetically sealed preparation from which 219 Rn radon gas could not escape . The spectrum therefore contains gamma lines and all daughter radionuclides of the decay series, with which 223 Ra is in radioactive equilibrium. The gamma lines derived from the conversion of 223-Ra to 219-Rn are given in the spectrum without labeling (only with energy value), for photopeaks from secondary transformations in the decay series, list the corresponding radionuclides from which they originate (especially 219Rn, 211 Bi, 211 Pb and 207 Tl).

One complete radioactive transformation of the 223 Ra nucleus in the whole decay series to a stable 207 Pb releases a total nuclear energy Q = 29.986 MeV , which is carried away by about 95% by four alpha particles , by 3% by beta + neutrons and by about 1% *) photons gamma and X-rays.
*) This seemingly small percentage of photon radiation is due to the energy conversion with respect to high-energy
a-particles. In fact, the absolute number of gamma and X photons emitted is relatively high, for energies in the range of 80-400keV represents about 96%! The most represented X and gamma-energies are: X 81 (14%), 83 (25%) and 95keV (8%), gamma 154 (5.8%), 269 (14%), 351 (13%) and 401keV (7%).
  Radium 223 Ra and daughter products of the decay series use mainly emitted alpha-radiation with energies of 5.4-7.4 MeV (a total of 4 alpha-particles / 1 conversion of 223 Ra ) in nuclear medicine for radioisotherapy of bone metastases , which often occur in breast and prostate cancer (3.6, part " Radioisotope therapy ", passage " Radionuclide therapy of tumors and metastases "). Beta electrons are of negligible importance. Radium has a calcium-like chemical and biological behavior, so that 223 Ra accumulates in metabolically active bone tissue in hydroxyapatite crystals. It is therefore taken up in bone metastases with increased osteoblastic activity , where it unfortunately shows only a palliative effect in the osteoblastic margin of the metastasis (alpha-particles practically do not interfere with the tumor tissue itself) .
  The manner in which the parent 223 Ra is converted to a number of shorter radionuclides after its accumulation in the target tissue is a typical example of the aforementioned in vivo radionuclide generator .
  Gamma radiation
223Ra and its daughter nuclides are practically not used in therapy, but can be used for gammagraphic monitoring of the distribution of radiopharmaceuticals in the body. The positive significance of the relatively large proportion of gamma radiation also lies in the possibility of easily measuring the activity of 223 Ra preparations in conventional activity meters with an ionization chamber (2.3 " Ionization chambers ") , using the appropriate gamma constant calibration.

Actinium Ac 89 is a soft silvery white metallic element, highly radioactive , has no stable isotope. In nature, two isotopes of actinium occur in trace amounts: 227 Ac (T1/2 = 21.77 years) and 228 Ac (T1/2 = 6.15 hours), as part of the decay series of uranium-235 and thorium-232. They decay by alpha (or branched beta-alpha) radioactivity to the corresponding francium (or thorium) isotopes and further by a 4-6 member decay series to stable lead isotopes. The name of the element originated from its strong radioactivity (Greek aktis = ray ) . The isotopes of actinium 206-234Ac are known in nuclear physics . The most important of these - for radionuclide therapy in nuclear medicine - is the artificially produced isotope actinium-225 :
Actinium 225 Ac
With a half-life of 10 days, it is converted by alpha-radioactivity to francium
221 Fr - in 50% to the ground state (emission Ea = 5.83MeV), in other cases to a number of excited states of francia (several tens of gamma photons are emitted during deexcitation , from low energies approx. 10keV, weaker peaks are up to 800keV) . Further radioactive transformations of 221 Fr then continue through the entire decay series up to bismuth 209 Bi - it is part of the neptunium series :

  Actinium 225 Ac is transformed by a whole decay series of 6 main daughter nuclei :
(
225 Ac (10d .; a ) 221 Fr (4.8m .; a ) 2 17 At (32ms .; a ) 213 Bi (46m .; b- ) 213 Po (4 m s .; a ) 209 Pb (3.3 h .; b- )
209 Bi (stab.) ) - picture on the left.
Note:
209 Bi can be considered stable here ( a , T1/2 2.10 19 years).
  In the first conversion of 225 Ac (to franicum 221 Fr) alpha radiation with an energy of 5.8 MeV and weak gamma radiation of 63, 100, 110, 150 keV are emitted, higher energies of 250-760keV have a small representation.
  During the radioactivity of the daughter nuclides of the decay series, a number of other energies of alpha, beta and gamma photons are emitted: of
 221 Fr it is a 6.3 MeV and gamma radiation with energy mainly 218 keV; of 217 At it's a 7.06 MeV; from 213 Bi it is alpha 5.8MeV, beta 987keV and gamma 440 keV; of 213 Po is alpha 8.4MeV; of 209 Pb it is beta 644keV.
  
The secondary branch 213 Bi (a) 209 Tl is not more important in applications due to its low proportion (2.1%).
  The 225-Ac decay chain functions as "in vivo radionuclide generator "- see above" In vivo generators ".
  A simplified conversion scheme of 225 Ac to 221 Fr and another decay chain is drawn below in the left part of the figure.
  The measured spectrum of gamma radiation emitted by all nuclides from the whole 225-Ac decay series is shown below the right portion of fig.
Conversion scheme of actinium 225 Ac (first conversion to francium-221, simply next chain) and the total gamma spectrum of 225 Ac and its decay products.
The spectrum contains gamma lines and all daughter radionuclides of the decay series, with which 225 Ac is in radioactive equilibrium. At the bottom of the figure is an enlarged section of the spectrum of the low-energy region of about 50-230 keV, where there is a large inflation of gamma and X peaks.
Actinium-225 alone, when alpha-converted to 221-Fr, produces relatively little gamma radiation (only faint peaks of 63, 100, 150, 188 keV are visible in the spectrum). Most gamma radiation of actinium preparations comes from daughter radionuclides of the decay series, mainly from
221 Fr (218keV) and 213 Bi (440keV).

One complete radioactive transformation of the 225Ac nucleus in the entire decay series to a stable 209 Bi releases a total nuclear energy Q = 31 MeV , which is carried away by about 95% by four alpha-particles , by 3% beta + neutrinos and by about 1% gamma photons and X-rays. For actinium 225 Ac and daughter products of the decay series, emitted alpha radiation with energies of 5.8-8.4 MeV (a total of 4 alpha particles / 1 conversion of 225Ac ) is used in nuclear medicine for biologically targeted radionuclide therapy . Radiopharmaceuticals labeled with 225 Ac (including monoclonal antibodies, eg 225Ac-Trastuzumab or 225Ac-PSMA-617) are being tested for the treatment of leukemia, lymphomas, neuroendocrine tumors, gliomas, melanomas, and are very promising in the prostate.
  Radiation of gamma daughter nuclides 225 Ac is practically not contribute in therapy, but can be used for gammagraphic monitoring of the distribution of radiopharmaceuticals in the body. Emission of gamma radiation , especially energy 218keV, allows simultaneous scintigraphic imaging during therapy tissues and organs into which the therapeutic preparation has penetrated. On these scintigraphic images we can assess (visually, or even quantitatively) the degree of desirable uptake of radiopharmaceuticals in tumor foci and unwanted accumulation in healthy tissues and critical organs - to monitor the course of radioisotope therapy .
  Preparation: Isotop 225 Ac in larger quantities is still difficult to obtain. It can be obtained as a product of radioactive alpha + beta conversion of thorium 229 Th ( a , T1/2 = 7340 years) 225 Ra ( b- , T1/2 = 14.8 days) 225 Ac - thorium-actinium 229Th / 225Ac generator , from which a smaller amount of actinium has so far been obtained for experimental use in nuclear medicine. Thorium-229 is gained from a -decay of uranium 233 U, whose supplies are very limited. Actinium-225 is artificially prepared in a cyclotron by irradiating radium-226 with protons (optimal energy 17MeV) by reacting 226 Ra (p, 2n) 225 Ac.
Actinium 227 Ac
With a half-life of 21.77 years, it is branched by beta
- -radioactivity to 227Th (98.6%) and alpha-radioactivity to 223 Fr (1.4%), then by decay series .... It is produced by irradiating radium-226 neutrons in a nuclear reactor: 226 Ra (n, g ) 227 Ra ( b- , T1/2 = 41min.) 227Ac. Actinium 227 Ac is used as the parent isotope for the generator preparation of the above-described thorium 227-Th and radium 223-Ra .
  Among the decay products of thorium and uranium is the gaseous radioisotope radon :
Radon Rn 86 is the heaviest element in the group of rare gases. It is radioactive, it has no stable isotope. In nature, three isotopes of radon occur in trace amounts: 222 Rn (T1/2 = 3.82 d.), 220 Rn (T1/2 = 54.5 s.) and 219 Rn (T1/2 = 3.92 s.). They come from the decay series of uranium and thorium, specifically they arise during the alpha-radioactivity of radium isotopes. They decay into the appropriate isotopes of polonium and further by a decay series of 4-6 members into stable isotopes of lead. The original name of radon was radio emanation - emanating from radio. And radon 220Rn was formerly called thoron (it is part of the thorium decay series -Fig.1.4.1 left) .
Radon 222 Rn
Alpha-decay of radium-226 produces gaseous radon
222 Rn , which is further converted with a half-life of 3.83 days by alpha-radioactivity to polonium 218 Po, in 99.92% to the ground state, in 0.08% to the excited level 510keV. Further radioactive transformations then take place throughout the decay series according to the right part of Fig.1.4.1 . The gamma spectrum of radon-222 is almost identical to the above spectrum of 226 Ra (except for the 186keV line). Secondary natural radon-222 with its decay products is important from the point of view of radioecology - see chapter 5, 5.2 "Biological effects of ionizing radiation ", section" Sources of ionizing radiation ".
  Radons
220 Rn in thorium and 219 Rn in uranium-actinium decay series due to their short half-life are sufficient to decay before diffusion escapes from radioactive material, so there is no need to consider in radioecology.

Transurans
Of the artificially produced heaviest nuclei of the transuranic group
(elements heavier than uranium - they are discussed in detail in 1.3, part " Transurans ") , three radionuclides have a practical application :
Plutonium 239 Pu
Plutonium
239 Pu with a half-life of T1/2 = 24100 years by alpha -radioactively decays to uranium 235 U (to excited levels of 51.7, 13.4 and 0.007 keV; however, gamma radiation is almost not emitted here, because the respective transitions are almost completely subject to internal conversion, so that conversion and Auger electrons are emitted instead) . Further transformations are taking place throughout uranium-actinium decay series (middle part of Fig.1.4.1 ) . Plutonium-239 is formed in a nuclear reactor by neutron fusion from uranium 238 U: 238 U (n, g ) 239 U (b- ; 25min ) 239 Np (b- ; 2.3 days ) 239 Pu. It is an effective fissile material (similar to uranium 235U). In addition to misuse for nuclear weapons, it is used in special nuclear reactors (1.3, section " Fast breeding reactors FBR ").
Americium 241 Am
Americium
241 Am decays with a half-life T1/2 = 458 years by alpha-radioactivity to neptunium 237 Np (and then by the whole neptunium decay series - shown above in the passage " Actinium 225 Ac ", in the diagram on the top left) . Alpha-decay of 241Am occurs mainly (in 84.6%) to an excited level of 59.6 keV of neptunium, which emits 59.6 keV gamma radiation when deexcited to the ground state , 23.6 keV gamma is weakly represented. As a result of the internal conversion, the characteristic X-radiation L is further emitted La,b of neptunium 11-22keV. A large number of other excited levels of 237Np (33, 75-1014 keV) are saturated with negligible intensity and have no significance for 241 Am radiation . 241-americium is thus a mixed a + g emitter : Ea = 5485keV, Eg = 59.6keV. Due to the very long half-life of the daughter 237 Np, the radiation of other members of the decay series is negligibly low compared to americium.
  The 241 Am isotope is formed in a plutonium in nuclear reactor by neutron fusion in reactions 239 Pu (n, g ) 240 Pu (n, g )  241 Pu (b- ) 241 Am.
  Americium-241 is often used as a standard soft gamma radiation 59.6 keV, as source of a particles e.g. in the ionization fire detectors, mixed with beryllium using reaction ( a , n) as a laboratory source of neutrons (1.6, section " Neutron radiation and its interactions ") .


Decomposition scheme and gamma spectrum of americium
241 Am .

Californium 252 Cf
is the heaviest radionuclide, which still has a practical application. Californium
252Cf (T1/2 = 2.65 years) decays, in addition to a-radioactivity (97%) to 248 Cm, by spontaneous fission (3%) *), in which neutrons are emitted (approx. 3.7 neutrons / 1 fission ) - it is therefore used as an intensive neutron source , eg for neutron activation analysis and for neutron capture radiotherapy (chapter 3.6., section " Neutron Therapy ") . Californium-252 is formed from a plutonium- 239Pu in nuclear reactor by gradual multiple neutron capture, combined with beta- transformations.
*) Note: From the point of view of neutron production, perhaps even more interesting would be the isotope 254 Cf, which decays with spontaneous fission even in 99% of cases; however, its disadvantage is more difficult preparation and shorter half-life T1/2 = 60.5 days.
  Transurans decay radioactively through entire decay series (similar to uranium and thorium - see Figure 1.4.1 above ) , where individual daughter products show alpha and beta radioactivity and excited nuclei emit gamma radiation. The end product is stable isotopes of lead or bismuth (if overlook a the very low radioactivity of 209Bi with a half-life of 1.9.1019 years) .

Below is a very brief table of some of the most important radionuclides, which serves only to illustrate the theoretical analysis of radioactivity in 1.2 and the properties of radionuclides in this 1.4. A complete and detailed overview of radionuclides, with decay schemes and all their characteristics, can be found, for example, in the excellent " Table of isotopes " by Lederer, Hollander, Perlman (new electronic version http://ie.lbl.gov/toipdf/toi20 .pdf ) .

Table of the most frequently used radionuclides

Radionuclide Half time T 1/2 Method of
disintegration
Energy [ keV ]
E a or E b max
Energy [ keV ]
gamma E g
The most common
method of production
Use
1 n 0 13 min b - 782 - reactor 235 U,
( a , n)
nuclear
analysis
3 H 1 12.3 years b - 18.6 - 6 Li (n, a ) 3 H biology
14 C 6 5730 years b - 156 - 14 N (n, p) 14 C biology
analysis
18 F 9 110 min. b + (97%)
EC (3%)
633 511 (194%)
(annihilation)
18 O (p, n) 18 F nuclear
medicine
32 P 15 14.3 days b - 1710 - 32 S (n, p) 32 P nuclear
medicine
40 K 19 1.28. 10 9
years
b - (89%) EC (11%)
1314 1460 (11%) natural
radionuclide
isotope.
dating
51 Cr 24 27.7 days EC - 320 (9.8%) 50 Cr (n, g ) 51 Cr nuclear
medicine
57 Co 27 271 days EC - 14 (9%)
122 (86%)
136 (11%)
692 (0.15%)
56 Fe (d, n) 57 Co
56 Fe (p,
g ) 57 Co
55 Mn (
a , 2n) 57 Co

gamma source
58 Co 27 70.8 days b + , EC - 511 (30%)
810 (99%)
865 (1.5%)
1670 (0.6%)
55 Mn ( a , n) 58 Co biology,
nuclear
medicine
60 Co 27 5,271 years b - 310 (99.88%)
1480 (0.12%)
1173 (100%)
1332 (100%)
59 Co (n, g ) 60 Co
gamma source
67 Ga 31 3.26 days EC - 93 (40%)
184 (20%)
300 (17%)
393 (5%)
68 Zn (p, 2n) 67 Ga nuclear
medicine
68 Ga 31 68 min. b + (89%)
EC (11%)
  511 (178%)
(annihilation)
68 Zn (p, n) 68 Ga nuclear
medicine
81 Rb 37

4.6 hours

EC is

- 190 (66%)
446 (19%)
79 Br ( a , 2n) 81 Rb
generator
81m Kr

81m Kr 36 13 sec. IT - 190 (67%) 81 Rb 81m Kr
lung scintigraphy
90 Sr 38 28.8 years b - 546 - 235 U (n, f) 90 Sr  
90 Y 39 64 hours b - 2280 - 90 Sr 90 Y
89 Y (n,
g ) 90 Y
nuclear
medicine
99 Mo 42

66 hours

b -

436 (17%)
1214 (83%)
140 (6%)
181 (7%)
740 (13%)
778 (5%)
98 Mo (n, g ) 99 Mo
235 U (n, f) 99 Mo
generator
99m Tc

99m Tc 43 6 o'clock IT - 140 (90%) 99 Mo 99m Tc scintigraphy
111 In 49 2.8 days EC - 171 (90%)
245 (94%)
111 Cd (p, n) 111 In nuclear
medicine
123 I 53 13.2 hours EC - K a 27 (71%)
K b 31 (16%)
159 (83%)
121 Sb ( a , 2n) 123 I nuclear
medicine
125 I 53 60 days EC - K a 27 (112%)
K b 31 (25%)
35 (6.5%)
124 Xe (n, g ) 125 Xe
EC
125 I
nuclear
medicine
(RIA)
131 I 53 8.04 days b - 334 (7.5%)
606 (90%)
80 (2.5%)
284 (6%)
364 (81%)
637 (7%)
723 (2%)
130 Te (n, g ) 131 Te
235 U (n, f) 131 Te
b - (25min) :
131 Te
131 J
nuclear
medicine
133 Xe 54 5.3 days b - 346 K a 31 (39%)
K b 35 (9%)
81 (37%)
235 U (n, f) 133 Xe nuclear
medicine
137 Cs 53 30 years b - 1176 K a  32 (6%) K b 36 (1.5%) g 662 (85%)  

 
235 U (n, f) 137 Cs
gamma source
             
             
             
             
             
192 Ir 77 74.2 days b - (95%)
EC (5%)
240 (8%)
536 (41%)
672 (46%)
296 (29%)
308 (30%)
317 (81%)
468 (49%)
604 (9%)
612 (6%)
191 Ir (n, g ) 192 Ir
192 Os (d,
2 n) 192 Ir

gamma source
201 Tl 81 73 hours EC - K a 70 (74%)
K b 80 (21%)
135 (2.6%)
167 (9%)
203 Tl (p, 3n) 201 Pb
EC
201 Tl
nuclear
medicine
             
226 Ra 88 1602
years
a 4782 186 (4%) natural
radionuclide

alpha source
232 Th 90 1.41. 10 10
years
a 4011   natural
radionuclide
potential
nuclear
fuel
235 U 92 7.1. 10 8
years
a 4580 143 (11%)
185 (54%)
204 (5%)
natural
radionuclide
fissile
material
238 U 92 4.51. 10 9
years
a 4195   natural
radionuclide
nuclear
reactor
239 Pu 94 2.44. 10 4
years
a 5160   238 U (n, g ) 239 U (b - ) 239 Np 3 (b - 239 Pu

fissile
material
241 Am 95 458 years a 5486 L a  13.9 (14%)
L b 17.8 (20%)
L g 20.8 (  5%) g 26.4 ( 3%) g 59.6 (36%) 
  
 
239 Pu (n, g ) 240 Pu
(n,
g ) 241 Pu
b -
241 Am

alpha
and
gamma source
252 Cf 98 2.65 years a (97%)

spont.
cleavage
(3%)
n
a:
6119 (97%)
+
cleavage fragm.
+
neutrons
- 238 U, 239 Pu
(n,
g ), (n, g ), ....
..., (n,
g ), .. b - ...

252 Cf

neutron source

Note: Pairs of parent daughter radionuclide used in generatorsare marked with a colored background.

1.3. Nuclear reactions   1.5. Elementary particles

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