Biological effects of ionizing radiation - risks and uses for health

AstroNuclPhysics Nuclear Physics - Astrophysics - Cosmology - Philosophy
Radiation as an important natural phenomenon

Influence of ionizing radiation on life

Use of radiation in diagnostics and therapy

Lecturer: RNDr. Vojtech Ullmann

- lecture syllabus -

Radiation - an important natural phenomenon

(in general)

  = Energy transfer through space
"at a distance"
by means of physical fields or microparticles
    In addition to radiation energy, there is also the transfer of matter and information
Energy transfer mechanism:
Time changes of field strength Particle motion
( Waves - electromagnetic, gravitational ) (electrons b, a -particles, protons, neutrons, ...)
cosmuscular-wave dualism

Radiation propagation in space:
Vacuum - free wave propagation and particle motion - according to the law of inertia
Substance environment - partial passage
                                            - scattering
- absorption - re-emission attenuation of radiation
change of radiation spectrum   

Energy transfer
mediates Information transfer

Radiation transmits informations :
About the source emitting radiation (its nature, composition, "strength", possibly variability, etc.)
About the material environment through which the radiation passes (density, thickness, chemical composition of the material environment)

Encoding information in :   Decoding of information :
Radiation intensity Radiation detection
Energy distribution Radiation spectrometry

Radiation helps to reveal :
The secret of the composition of matter
The structure and evolution of the universe (especially stars and galaxies, global cosmological issues)
Anatomical structure and physiological processes in living organisms

Radiation energy:
Helps to treat some diseases, especially cancer
It is used in radiation technologies

Light - A source of visual information about the world

What is light?

Both theories are partly right - they describe two different aspects of one phenomenon :

Remarkable property of light: independence of the speed of light (c = 300,000 km/s) on the mutual movement of the source and the observer Einstein's special theory of relativity .

Radiation in general :

However: Corpuscularly - wave dualism !

The rest mass m0 of the radiation quantum decides :

m0 > 0 corpuscular ; m0 = 0 wave

Corpuscular radiation:

Wave radiation:

Energy and radiation effects :

Ionizing radiation:

It is radiation whose quantums have such a high energy that they are able to eject electrons from the atomic shell and thus cause ionization of substances.

For conventional types of radiation photon (X, g), the electron (b-), and a is taken as the energy limit of ionizing radiation the energy of quant 5 keV .
The situation is more complicated with neutron radiation, where even very slow neutrons enter the nuclei and can cause secondary ionization through nuclear reactions (even delayed or longer-term - activation of nuclei, formation of radionuclides). Similarly, the threshold energy is not defined for
b+ radiation, where even very slow positrons annihilate with electrons to form hard ionizing radiation g .

Physics of ionizing radiation - radiation physics - radiology - dosimetry

RADIOLOGY = radiation science in general ; in medicine: RADIOLOGY = use of radiation for diagnosis and therapy

The physics of ionizing radiation is also known as radiation physics or radiophysics. It covers a wide range of issues :
Mechanisms of radiation formation
Physical properties of radiation
Interaction of radiation with matter (including radiobiological effects)
Detection and spectrometry of radiation
Mathematical analysis and evaluation of results
   A special area of radiation physics is radiological physics , dealing with physical aspects of radiation in medicine. Dosimetry of ionizing radiation is a field of radiation physics, which deals with the measurement and effects of radiation on substances in relation to the types and properties of radiation - substance interaction and the amount of radiation absorbed in the substance (absorbed energy - "dose") - 5.1 "Effects of radiation on matter". The studied substance is mainly living tissue, model measurements of doses and dose rates are performed in water, air and in special dosimetric phantoms.
Radiology - radiation in biology and medicine
From the etymological point of view, the word radiology generally means the science of radiation. However, historical developments have narrowed and specialized its significance. Radiology is now a science of the importance and use of radiation in medicine and biology, a medical field that uses ionizing radiation for diagnosis and therapy. It mainly includes three main special fields :
l X-ray diagnostics, also called radiodiagnostics *) (3.2 "X-ray diagnostics") .
l Radiotherapy (3.6 "Radiotherapy") .
l Nuclear medicine (Chapter 4 "Radioisotope scintigraphy")
*) During the development, other diagnostic methods that do not use ionizing radiation were included in radiodiagnostics - ultrasonic sonography (see Ultrasound sonography), nuclear magnetic resonance (Nuclear magnetic resonance) and thermography (Thermography).
   Radiobiology deals with the biological effects of ionizing radiation (see 5.2 "Biological effects of ionizing radiation") - a field on the border of radiation physics and biology.

Emergence and sources of radiation : (natural - artificial )

Radioactivity :

A physical phenomenon in which atomic nuclei transform spontaneously, whereby ionizing radiation is emitted .

Radioactivity a:

Occurs only in the heaviest nuclei - in the area of uranium and transuranium. Radiation a has a very short range in the substance - a limited importance.

Radioactivity b - :

The electron b- is formed in the nucleus by the transformation of the neutron: n0 p+ + e- + n

Radioactivity b + :

The positron b+ is formed in the nucleus by the transformation of a proton: p+ n0 + e+ + n

The spectrum of radiation b is continuous - the energy of transformation is divided between the particle b and the neutrino n .

Internal mechanism of beta radioactivity :
Transmutation of quarks "d" and "u" inside neutrons and protons due to a weak interaction mediated by intermediate bosons W -,+, which then decay into electrons or positrons and neutrinos.

Radiation g :
Gamma radiation is high-energy electromagnetic radiation generated by deexcitation of excited levels of the atomic nucleus .
In radioactivity it is the deexcitation of excited levels of the daughter nucleus formed after radioactive transformation .
Gamma radiation of non-nuclear origin
In addition to deexcitation of excited energy levels in atomic nuclei, g radiation is also produced by annihilation of positrons with electrons ,and also other particles and antiparticles, as well as by interactions of high-energy particles (g radiation of energies of the order GeV, TeV and higher). The category of radiation g also includes braking radiation generated by the impact of high-energy electrons on a target.

Basic properties of gamma radiation: - Penetration

Interaction of ionizing radiation with matter :

Interaction of alpha and beta radiation

Interaction of gamma radiation with matter in four ways :

1. Photo effect 2. Compton scattering 3. Formation of electron-positron pairs 4. Nuclear photo effect

Effects of ionizing radiation in matter and life

Influence of ionizing radiation on matter :
On elements: Ionization of atoms recombination on the same atoms - no chemical effects.
On compounds: Ionization of atoms chemical reactions radiolysis of compounds reactions of radicals formation of new compounds.
The "gateway" to chemical reactions opens - the more complex the compound, the more diverse the radiation-induced reactions.

Influence of ionizing radiation on living tissue:
Cells - basic units of living organisms

Influence of ionizing radiation on cells and DNA :

Radiobiological effects at the subcellular level. a) Interventional and radical mechanism of the effect of radiation on living tissue.
Above: When radiation enters the DNA macromolecule, ionization and a direct destructive effect occur. Bottom: Ionizing radiation interacts with the water molecule, radiolysising of water occurs: H2O H + + OH - - formation of free radicals . Highly reactive H + and OH - radicals attack complex organic molecules and chemically change them. DNA is disrupted in the nuclei of cells.
b) Different types of DNA damage due to radiation and chemical influences (rough schematic representation)
. c) Radiation effects during the cell cycle.

Schematic representation of significant processes and their time sequence in the effects of ionizing radiation on living tissue.

Small doses
Low ion density small number of DNA damage high probability of repair mechanisms for DNA repair
stochastic effects

High doses of radiation
High ion density
large number of damages repair mechanisms fail part of the cells dies
deterministic effects radiation sickness

Linear-quadratic (LQ) model : N = N0.e-(a.D+b.D2) T -ln (N/N0) = a.D + b.D2 - linear-quadratic dependence

Some deviations from the LQ model of dose-response of biological effect.
Multiple interactions of radiation with cells lead to the presence of members with a higher exponent of dose D . b) The bystander effect slightly increases the total number of damaged cells (decreases the fraction of surviving cells). c) In the area of low doses, a relatively increased cell sensitivity - hyperradiosensitivity - is observed on the graph of the surviving fraction of cells .

Bystander effect.
Radiation damage to a single cell can induce damage to some surrounding cells, that have not been irradiated.


Noxiously effects of ionizing radiation the need for radiation protection !

Use of ionizing radiation in medicine

X-ray trans-illumination of the organism
- image of tissue density -
X-ray diagnostics :

  Application of radioindicator detection of outgoing gamma radiation diagnostics of structure and function of organs
Radionuclide scintigraphy - nuclear medicine : + In vitro laboratory methods - radioimmunoassay (RIA)

Targeted irradiation of pathological tissue with a large (lethal) dose of radiation
destruction of tumor cells .
Basic task: Achieve the largest possible dose at the target site with the least possible damage to the surrounding tissues .
Teletherapy - external beam radiation rays ("remote")
Isocentric radiotherapy - radiation from several angles :

Modern methods for high-precision radiotherapy
stereotactic radiotherapy SBRT :

 - hadron radiotherapy : irradiation with accelerated protons (or a-particles, or carbon nuclei) and the use of peak Bragg curves (indicating the depth dependence of the effective dose) at the end of the braking path of the particle :

- Brachytherapy - introducing emitters "near", into or around tumors :

 - Radioisotope therapy open emitters beta or alpha - the "most close brachytherapy" - up close at cellular level (e.g. thyroid treatment radioiodine 131I, radionuclide therapy of metastases, haematologic therapy radionuclide synovectomy)

Radiation and life in the natural environment

Ionizing radiation in the natural environment:

Cosmic radiation probably played an important role in the origin and evolution of life, in at least two ways :

Supernova explosion observed in 1054 in China Today, a Crab Nebula containing a pulsar inside - a rapidly rotating neutron star - is observed at that place
Massive flashes of cosmic rays - a deadly danger to life !


Rays of life - beneficial effects of radiation
- Without radiation there would be no life - origin, evolution, maintenance of life
- Radiation as a source of energy and information
- Use of radiation for diagnostics and therapy in medicine

N Rays of death - harmful and destructive effects of radiation
- Criminal misuse of nuclear energy for war purposes
- Improper and careless handling of ionizing radiation sources - radiation accidents
- Risks from natural radiation sources

Unjustified radiophobia when working with radiation :
With erudite work with knowledge of the matter and adherence to the principles of radiation protection, it can be achieved that working with ionizing radiation is no more dangerous and harmful than working with any other materials, machines and equipment .

Nuclear physics and physics of ionizing radiation
Nuclear and radiation physics Radiation detection and spectrometry Radiation applications
With cintigraphy Computer evaluation of scintigraphy Radiation protection
Gravity, black holes and space   -   time physics Anthropic principle or cosmic God
AstroNuclPhysics Nuclear Physics - Astrophysics - Cosmology - Philosophy

Vojtech Ullmann