Radiation - radiation (from radiare - to emit rays) - the propagation of energy in the form of waves or particles. Light, ultraviolet rays, infrared thermal radiation, microwaves, radio waves are all types of radiation. Part of the radiation is called ionizing due to its ability to cause ionization of atoms and molecules in the irradiated substance.

Ionizing radiation - radiation, the interaction of which with the environment leads to the formation of ions of different signs. This is a stream of particles or quanta that can directly or indirectly cause ionization of the environment. Ionizing radiation combines types of radiation that are different in their physical nature. Among them stand out elementary particles (electrons, positrons, protons, neutrons, mesons, etc.), heavier multiply charged ions (a-particles, nuclei of beryllium, lithium and other heavier elements); radiation having electromagnetic nature (g-rays, x-rays).

There are two types of ionizing radiation: corpuscular and electromagnetic.

Corpuscular radiation - is a stream of particles (corpuscles), which are characterized by a certain mass, charge and speed. These are electrons, positrons, protons, neutrons, nuclei of helium, deuterium, etc.

Electromagnetic radiation - flux of quanta or photons (g-rays, X-rays). It has neither mass nor charge.

Distinguish also directly and indirectly ionizing radiation.

Directly ionizing radiation - ionizing radiation, consisting of charged particles with kinetic energy sufficient for ionization in a collision (, particle, etc.).

Indirectly ionizing radiation - ionizing radiation, consisting of uncharged particles, and photons that can directly create ionizing radiation and (or) cause nuclear transformations (neutrons, X-rays and g-radiation).

The main properties ionizing radiation is the ability, when passing through any substance, to cause the formation of a large amount free electrons and positively charged ions(i.e. ionizing capacity).

Particles or a quantum of high energy usually knock out one of the electrons of the atom, which carries away a single negative charge. In this case, the rest of the atom or molecule, having acquired a positive charge (due to the deficit of a negatively charged particle), becomes a positively charged ion. This is the so-called primary ionization.

The electrons knocked out during the primary interaction, possessing a certain energy, themselves interact with the oncoming atoms, turn them into a negatively charged ion (occurs secondary ionization ). Electrons that have lost their energy as a result of collisions remain free. The first option (the formation of positive ions) occurs best of all with atoms that have 1-3 electrons on the outer shell, and the second (the formation of negative ions) - with atoms that have 5-7 electrons on the outer shell.

Thus, the ionizing effect is the main manifestation of the action of high-energy radiation on matter. That is why radiation is called ionizing (ionizing radiation).

Ionization occurs both in the molecules of inorganic substances and in biological systems. For the ionization of most of the elements that are part of biosubstrates (this means for the formation of one pair of ions), an energy absorption of 10-12 eV (electron volts) is required. This is the so-called ionization potential ... The ionization potential of air is 34 eV on average.

Thus, ionizing radiation is characterized by a certain radiation energy, measured in eV. An electron volt (eV) is an off-system unit of energy that a particle with an elementary electric charge acquires when moving in an electric field between two points with a potential difference of 1 volt.

1 eV = 1.6 x 10-19 J = 1.6 x 10-12 erg.

1keV (kiloelectron-volt) = 103 eV.

1 MeV (megaelectron volt) = 106 eV.

Knowing the energy of the particles, it is possible to calculate how many pairs of ions they are able to form along the path. Path length is the total length of the particle's trajectory (no matter how complicated it is). So, if a particle has an energy of 600 keV, then it can form about 20,000 pairs of ions in the air.

In those cases when the energy of the particle (photon) is not enough to overcome the attraction of the atomic nucleus and fly out of the atom, (the radiation energy is less than the ionization potential), ionization does not occur. by acquiring excess energy (the so-called excited ), for a fraction of a second goes to a higher energy level, and then abruptly returns to its original place and gives up excess energy in the form of a quantum of luminescence (ultraviolet or visible). The transition of electrons from outer to inner orbits is accompanied by X-rays.

However, the role excitement in exposure to radiation is secondary in comparison with ionization atoms, therefore, the commonly accepted name for high-energy radiation: “ ionizing ", Which underlines its main property.

The second name for radiation is " penetrating "- characterizes the ability of high-energy radiation, primarily X-ray and
g-rays, penetrate into the depths of matter, in particular, into the human body. The depth of penetration of ionizing radiation depends, on the one hand, on the nature of the radiation, the charge of its constituent particles and energy, and on the other, on the composition and density of the irradiated substance.

Ionizing radiation has a certain speed and energy. Thus, b-radiation and g-radiation propagate at a speed close to the speed of light. The energy, for example, of a-particles fluctuates in the range of 4-9 MeV.

One of the important features of the biological effects of ionizing radiation is invisibility, imperceptibility. This is their danger, a person cannot detect the effect of radiation either visually or organoleptically. Unlike rays of the optical range and even radio waves, which in certain doses cause heating of tissues and a feeling of warmth, ionizing radiation, even in lethal doses, is not recorded by our senses. True, the astronauts observed indirect manifestations of the action of ionizing radiation - the sensation of flashes with closed eyes - due to massive ionization in the retina. Thus, ionization and excitation are the main processes in which the radiation energy absorbed in the irradiated object is spent.

The resulting ions disappear in the process of recombination, which means the reunification of positive and negative ions, in which neutral atoms are formed. As a rule, the process is accompanied by the formation of excited atoms.

Reactions involving ions and excited atoms are extremely important. They underlie many chemical processes, including biologically important ones. The negative effects of radiation on the human body are associated with the course of these reactions.

Prof. Davydov A.V.

1. General information and terminology.

Ionizing radiation (ionizing radiation) is a flow of elementary particles or quanta of electromagnetic radiation, which is created during radioactive decay, nuclear transformations, deceleration of charged particles in a substance, and the passage of which through the substance leads to ionization and excitation of atoms or molecules of the medium.

Ionization of the medium can only be produced by charged particles - electrons, protons and other elementary particles and nuclei of chemical elements. The ionization process consists in the fact that a charged particle, the kinetic energy of which is sufficient to ionize atoms, when moving in a medium interacts with the electric field of atoms and loses part of its energy to knock out electrons from the electron shells of atoms. Neutral particles and electromagnetic radiation do not ionize, but ionize the medium indirectly, through various processes of transferring their energy to the medium with the generation of secondary radiation in the form of charged particles (electrons, protons), which ionize the medium.

Ionizing radiation is divided into photonic and corpuscular.

Photon ionizing radiation - these are all types of electromagnetic radiation arising from a change in the energy state of atomic nuclei, electrons of atoms or annihilation of particles - ultraviolet and characteristic X-ray radiation, radiation arising from radioactive decay and other nuclear reactions and when charged particles are decelerated in an electric or magnetic field.

Corpuscular ionizing radiation - fluxes of alpha and beta particles, protons, accelerated ions and electrons, neutrons, etc. Corpuscular radiation of a flux of charged particles belongs to the class of directly ionizing radiation. Corpuscular radiation of a stream of uncharged particles is called indirectly ionizing radiation.

Ionizing radiation source (ionizing radiation source) - an object containing radioactive material (radionuclide), or a technical device emitting or capable of emitting ionizing radiation under certain conditions. Designed to obtain (generate, induce) a flow of ionizing particles with certain properties.

Radiation sources are used in devices such as medical gamma therapy devices, gamma flaw detectors, density meters, thickness gauges, static electricity neutralizers, radioisotope relay devices, coal ash meters, icing alarms, dosimetry equipment with built-in sources, etc.

On the physical basis of radiation generation separate radionuclide sources based on natural and artificial radioactive isotopes, and physical and technical sources (neutron and X-ray tubes, charged particle accelerators, etc.).

For radionuclide sources, a distinction is made between open and closed radiation sources.

Open source of ionizing radiation(unsealed source) - when used, the release of radioactive substances contained in it into the environment is possible.

Sealed source of ionizing radiation(sealed source) - in which the radioactive material is enclosed in an enclosure (ampoule or protective coating) that prevents personnel from contacting the radioactive material and its release into the environment above permissible levels under the conditions of use and wear for which it is designed.

By type of radiation emit sources of gamma radiation, sources of charged particles and sources of neutrons. For radionuclide sources, this separation is not absolute, since in nuclear reactions that induce radiation, the main type of radiation from the source can be accompanied by a significant contribution from the accompanying types of radiation.

By appointment allocate calibration (exemplary), control (working) and industrial (technological) sources.

Industrial radiation sources They are used in various production processes and industrial installations (nuclear logging methods, non-contact methods for monitoring technological processes, substance analysis methods, flaw detection, etc.).

Control sources are used to check and adjust nuclear physics instruments and installations (spectrometers, radiometers, dosimeters, etc.) by monitoring the stability and repeatability of instrument readings in a certain geometry of the position of the source relative to the radiation detector.

Calibration sources used for calibration and metrological verification of nuclear physics equipment.

Technical characteristics of radiation sources:

1. 1. Type of radiation (for radionuclide - the main one for the purpose).
2. 2. Geometry of the source (shape and size). Geometrically, sources can be point and extended. Extended sources can be linear, surface, or volumetric.
3. 3. Activity (number of decays per unit time) and its distribution by source for radionuclide sources. Power or radiation flux density for physical and technical sources.
4. 4. Energy composition. The energy spectrum of sources can be monoenergetic (particles of one fixed energy are emitted), discrete (monoenergetic particles of several energies are emitted) or continuous (particles of different energies are emitted within a certain energy range).
5. 5. Angular distribution of radiation. Among the variety of angular distributions of radiation sources, for solving most practical problems, isotropic, cosine or mono-directional are usually specified.

GOST R 51873-2002 - Closed sources of ionizing radiation. General technical requirements. It was put into effect in 2003. The standard applies to sealed radionuclide sources of alpha, beta, gamma, X-ray and neutron radiation. Does not apply to exemplary and control sources, as well as to sources, the activity of radionuclides in which does not exceed the minimum significant, established by the "Radiation Safety Standards".

According to the standard, the sources must be sealed, with established strength classes, permissible climatic and mechanical influences in accordance with GOST 25926 (but not below the range from -50 to +50 o C and humidity not less than 98% at +40 o C). The service life of the source must be at least:

• - two half-lives - for sources with a half-life of less than 0.5 years;
• - one half-life (but not less than 1 year) - with a half-life from 0.5 to 5 years;
• - 5 years - for sources of gamma and neutron radiation with a half-life of 5 years or more. For sources of alpha, beta and x-ray radiation with a half-life of 5 years or more, the service life is established in a regulatory document for a specific type of source.

Sources are non-recoverable industrial products and cannot be repaired. If the radiation parameters are kept within the limits that satisfy the user, the tightness is maintained and there are no defects, the source's service life can be extended. The renewal procedure is established by the state administration bodies for the use of atomic energy.

Units of measurement of radioactivity and radiation doses.

A measure of the radioactivity of a radionuclide is its activity, which is measured in Becquerels (Bq). One Bq is equal to 1 nuclear transformation per second. Nonsystematic unit - Curie (Ci), activity of 1 g of radium (Ra). 1 Curie = 3.7 * 10 10 Bq.

Radiation dose - the amount of energy of ionizing radiation that is perceived by a certain medium for a certain period of time.

The absorbed dose is the energy absorbed by a unit mass of the irradiated substance. The unit of absorbed radiation dose is gray (Gy) = 1 joule per kilogram (J / kg).

The absorbed dose of various types of radiation causes a different biological effect per unit mass of biological tissue. The equivalent dose is equal to the product of the absorbed dose and the average radiation quality factor in comparison with gamma radiation. Coefficient values: X-rays, electrons, positrons, beta radiation -1, thermal neutrons - 3, protons, fast neutrons - 10, alpha particles and recoil nuclei - 20. Sievert (Sv) - dose any radiation absorbed by 1 kg of biological tissue and causing the same biological harm as the absorbed dose of photon radiation in 1 Gy. The non-systemic unit is rem. 1 Sv = 100 rem.

The exposure dose (D exp) serves to characterize the photon radiation and determines the degree of air ionization under the influence of these rays. It is equal to the radiation dose at which ions appear in 1 kg of atmospheric air, carrying an electricity charge of 1 coulomb (C). D exp = Cl / kg. Non-systemic unit - X-ray (R). 1 Р = 2.58 · 10 -4 C / kg.

Main radionuclides for environmental monitoring. The table below shows brief data on the nuclear-physical characteristics of radionuclides, the content of which in the environment, in building materials, in working and household premises and, especially, in agricultural food products, can be significant in terms of radiation hazard to human health.

	Name	half-life	quanta, MeV	Beta particles
226 Ra Þ 206 Pb 232 Th Þ 208 Pb	Uranium series Thorium series	1.4 10 10 year	A lot, up to 2.45 A lot, up to 2.62	Many, up to 3 Many, up to 3	Natural
	Strontium-Yttrium	30 years, 3 days			Technogenic
	Cerium-Praseodymium Ruthenium-Rhodium	285 days, 17 minutes 372 days, 30 sec.			Products

Radon-222, a decay product of Ra-226, deserves special attention. It is an inert gas, and is released from any media and objects (soil, building materials, etc.), which almost always contain uranium and its decay products. The average concentration of radon at ground level outdoors is 8 Bq / m 3. Radon has a half-life of 3.824 days and can accumulate in closed and poorly ventilated areas.

The population of the Earth receives the main part of the exposure from natural sources of radiation. These are natural radionuclides and cosmic rays. The total dose due to natural sources of radiation averages about 2.4 mSv per year.

2. Sources of charged particles.

Dozens of elementary charged particles are known, but the lifetime of most of them does not exceed microseconds. The elementary charged particles involved in nuclear reactions include beta particles (electrons and positrons), protons and alpha particles (helium nuclei 4 He, charge +2, mass 4).

Interaction of charged particles with matter. Charged particles are classified as low-penetrating types of ionizing radiation. When moving in matter, they interact with the electric fields of the atoms of the medium. As a result of the interaction, the electrons of the atoms of the medium receive additional energy and transfer to energy levels more distant from the nucleus (the process of excitation) or completely leave the atoms (the process of ionization). When passing near an atomic nucleus, a particle experiences deceleration in its electric field, which is accompanied by the emission of bremsstrahlung gamma radiation.

The path length of a particle in a substance depends on its charge, mass, initial kinetic energy, and on the properties of the medium. The mileage increases with an increase in the energy of the particle and a decrease in the density of the medium. Massive particles have lower velocities than light ones, interact with atoms more efficiently and lose their energy faster.

The range of beta particles in the air is up to several meters, depending on the energy. A layer of aluminum with a thickness of 3.5 mm, iron - 1.2 mm, lead - 0.8 mm completely protects from the flux of beta particles with a maximum energy of 2 MeV. Clothing absorbs up to 50% of beta particles. With external irradiation of the body, 20-25% of beta particles penetrate to a depth of more than 1 mm.

Alpha particles with a large mass, when colliding with electrons of atomic shells, experience very small deviations from their initial direction and move almost rectilinearly. The range of alpha particles in matter is very small. For example, an alpha particle with an energy of 4 MeV has a path length of about 2.5 cm in air, in water or in the soft tissues of animals and humans - hundredths of a millimeter.

Sources of beta radiation.

Beta radiation- corpuscular ionizing radiation, the flow of electrons or positrons that occurs during beta decay of atomic nuclei with the ejection of an electron or positron from the nucleus at a speed close to the speed of light.

Beta decay of radionuclides is accompanied by the emission of neutrinos, while the separation of the decay energy between an electron and a neutrino is random. This leads to the fact that the energy distribution of the emitted beta particles is continuous from 0 to the maximum energy E max determined for each isotope, the distribution mode is shifted to the low-energy region, and the average value of the particle energy is of the order of (0.25-0.45) E swing. An example of the energy distribution of beta radiation is shown in Fig. one.

Fig 1. An example of the distribution of beta radiation by energy

The shorter the half-life of the radionuclide, the greater the maximum energy of the emitted beta particles. The range of E max values ​​for various radionuclides extends from ten keV to ten MeV, but the half-lives of nuclides in the latter case are very small, which makes it difficult to use them for technological purposes.

The characteristic of the penetrating power of radiation is usually given by the average value of the absorption of radiation energy when radiation passes through a layer of matter with a surface density of 1 g / cm 2. The energy absorption of beta particles when passing through a substance is of the order of 2 MeV per 1 g / cm 2, and protection from radiation from radionuclide sources does not pose a problem. A 1 mm thick lead layer almost completely absorbs radiation with energies up to 2.5 MeV.

Sources of beta radiation (disk and point) are made in a thin-layer version on special substrates, the material of which significantly depends on the reflection coefficient of beta particles from the substrate (it increases with an increase in the atomic number of the material, and can reach tens of percent for heavy metals). The thickness of the active layer and the presence of a protective coating on the active layer depends on the purpose of the source and the radiation energy. For spectrometric measurements, the energy absorption of particles in the active layer and protective coating should not exceed 2-3%. The range of activity of sources is from 0.3 to 20 GBq.

Powerful sources are made in the form of sealed titanium or stainless steel capsules with a special exit window for beta radiation. So, the isotope installation "SIRIUS-3200" on a mixture of Sr-Y isotopes with an activity of 3200 Ci provides an output electron flux density of up to 10 8 electr · cm -2 · s -1.

Table 1 lists the most common radionuclide sources of beta particles.

Table 1. Radionuclide sources of beta particles.

Beta decay for most radionuclides is accompanied by strong gamma radiation. This is due to the fact that the final decay nucleus is formed in an excited state, the energy of which is removed by the emission of gamma quanta. In addition, when beta particles are decelerated in a dense medium, bremsstrahlung gamma radiation occurs, and the rearrangement of the electron shell of a new atom is accompanied by the appearance of characteristic X-ray radiation.

Industrial physical and technical sources charged particles - electron accelerators (microtrons, betatrons, linear wave accelerators) are used to obtain high-energy electron fluxes (more than 3-5 MeV).

Unlike isotopic sources with a continuous spectrum of electrons, accelerators produce a beam of electrons with a fixed energy, and the flux and energy of electrons can vary over wide ranges.

Fig 2. Accelerator ELV-8 (Novosibirsk)

In Russia, industrial accelerators of the ELV series with energy (0.2-2.5) MeV, power up to 400 kW, and the ILU series with energy (0.7-5) MeV, power up to 50 kW are used. The machines are designed for continuous operation in an industrial environment, equipped with a variety of electron beam scanning systems for irradiation of various products. They are used for radiation-chemical technologies used in the production of cable products with heat-resistant insulation, polymer pipes for hot water supply, heat-shrinkable pipes, cold-resistant polymers, polymer roll composite materials, etc. The pulsed accelerator RIUS-5 creates an electron current in pulses (0.02-2) μs up to 100 kA at an electron energy of up to 14 MeV. Small-sized pulsed betatrons of the MIB type are used for radiographic quality control of materials and products in non-stationary conditions.

Sources of alpha radiation.

Alpha radiation- this is corpuscular ionizing radiation, is a stream of alpha particles (nuclei of helium atoms) with an energy of up to 10 MeV, an initial speed of about 20 thousand km / s. These particles are emitted during the decay of radionuclides with a large atomic number, mainly transuranic elements with atomic numbers over 92. Their ionizing capacity is enormous, and the penetrating ability is negligible. The path length in air is 3-11 cm (approximately equal to the energy of particles in MeV), in liquid and solid media - hundredths of a millimeter. A layer of matter with a surface density of 0.01 g / cm 2 completely absorbs radiation with an energy of up to 10 MeV. External alpha radiation is absorbed in the stratum corneum of the human skin.

In radionuclide sources of alpha radiation, alpha decay of unstable nuclei of both natural isotopes and heavy artificial isotopes is used. The main energy range of alpha particles in decay is from 4 to 8 MeV. The energy distribution of radiation is discrete and is represented by alpha particles of several energy groups. The yield of alpha particles with maximum energy is usually maximum, the width of the energy lines of radiation is very small. For the manufacture of radionuclide alpha sources, isotopes with the maximum yield of alpha particles and with the minimum accompanying gamma radiation are used. Sources are manufactured in a thin-layer version on metal substrates.

Table 2. Radionuclide sources of alpha particles.

Nearly pure alpha emitters (such as polonium-210) are excellent energy sources. The specific power of the emitter based on Ро-210 is more than 1200 watts per cubic centimeter. Polonium-210 served as a heater for Lunokhod-2, maintaining the temperature conditions required for the operation of the equipment. As an energy source, polonium-210 is widely used as a power source for remote beacons. It is also used to remove static electricity in textile factories, ionize air for better fuel combustion in open-hearth furnaces, and even to remove dust from photographic films.

Low-level sources are also produced, which are used as radiation standards for calibrating radiometers, dosimeters and other measuring equipment. Exemplary sources of alpha radiation are made on the basis of isotopes uranium-234 and 238, plutonium-239.

The physical and technical sources of beams of helium ions, protons or heavy ions include the cyclotron. It is a proton (or ion) accelerator in which the frequency of the accelerating electric field and the magnetic field are constant over time. Particles move in a cyclotron along a flat unfolding spiral. The maximum energy of accelerated protons is 20 MeV.

3. Sources of electromagnetic (photon) radiation.

Sources of gamma radiation.

Gamma radiation (gamma radiation) - short-wave electromagnetic radiation with a wavelength of less than 0.1 nm, which occurs during the decay of radioactive nuclei, the transition of nuclei from an excited state to the ground state, during the interaction of fast charged particles with matter, annihilation of electron-positron pairs and other elementary transformations particles. In view of the fact that nuclei have only certain allowed levels of the energy state, the spectrum of gamma radiation is discrete and, as a rule, consists of several groups of energies in the range from several keV to ten MeV. For radionuclides with large atomic numbers, the number of energy groups of gamma quanta can reach several tens, but they differ sharply in the probability of release, and the number of quantum lines with the highest yield is usually small.

The flux of gamma quanta has wave and corpuscular properties and propagates at the speed of light. The high penetrating power of gamma radiation is due to the absence of an electric charge and a significant amount of energy. The intensity of gamma ray exposure decreases in inverse proportion to the square of the distance from the point source.

Gamma quanta interact mainly with the electron shells of atoms, transferring part of their energy to electrons in the process of the photoelectric effect and the Compton effect. In the photoelectric effect, a photon is absorbed by an atom of the medium with the emission of an electron, and the energy of the photon minus the binding energy of the electron in the atom is transferred to the liberated electron. The probability of the photoelectric effect is maximum in the region of photon energies below 200 keV, and rapidly decreases with increasing photon energy. In the case of the Compton effect, only a part of the photon energy is spent on knocking out an electron from the atomic shell, and the photon itself changes the direction of motion. Compton scattering dominates in the energy range (0.2-5) MeV and is proportional to the atomic number of the medium. When the photon energy is higher than 1.022 MeV near the atomic nucleus, the formation of electron-positron pairs becomes possible, the probability of this process increases with increasing photon energy.

The paths of gamma quanta in the air are measured in hundreds of meters, in solid matter - in tens of centimeters. The penetrating power of gamma radiation increases with an increase in the energy of gamma quanta and decreases with an increase in the density of the medium. Attenuation of photon-ionizing radiation by a layer of matter occurs exponentially. For a radiation energy of 1 MeV, the thickness of the tenfold attenuation layer is about 30 g / cm 2 (2.5 cm of lead, 4 cm of iron, or 12-15 cm of concrete).

Radionuclide sources of gamma quanta - natural and artificial beta-active isotopes (table 3), cheap and easy to use. In beta decay of nuclides, the nucleus, a decay product, is formed in an excited state. The transition of an excited nucleus to the ground state occurs with the emission of one or several successive gamma quanta, which remove the excitation energy. Radionuclide sources are sealed stainless steel or aluminum ampoules filled with an active isotope. The energy of gamma quanta of radionuclide sources does not exceed 3 MeV.

Table 3. Radionuclide sources of gamma radiation.

	Name	half-life	Energy of lines radiation, keV	Quantum yield
	Cobalt-60 Strontium-85 Antimony-124 Iridium-192		120; 136; 265; (280; 400) 610; 640-1450; 1690; 2080	100; 35; 50; 6.5

Currently, powerful sources of gamma radiation have found application in medicine (radiotherapy, sterilization of instruments and materials), in geology and mining (density measurement, ore sorting), in radiation chemistry (radiation-chemical modification of materials, polymer synthesis), and in many others. industries of industrial production and construction (defectoscopy, mass measurement, thickness measurement of materials and much more).

In the radiological departments of oncological dispensaries, sealed radionuclide sources with a total activity of up to 5 * 10 14 Bq are operated. Portable gamma-ray flaw detectors such as "Gammarid" and "Stapel-5M" based on iridium-192 have sources with an activity of 85 to 120 Bq.

Physical and technical radiation sources are electron accelerators that are used to generate gamma rays. In these accelerators, the electron flux is accelerated to energies of several MeV and is directed to a target (zirconium, barium, bismuth, etc.), in which a powerful flux of gamma quanta of bremsstrahlung radiation with a continuous spectrum from zero to the maximum electron energy arises.

LIU-10, LIU-15, UIN-10, RIUS-5 devices are used to create powerful pulsed gamma-ray bremsstrahlung fluxes. The pulsed accelerator RIUS-5 creates an electron current in pulses (0.02-2) μs up to 100 kA at an electron energy of up to 14 MeV, which makes it possible to create a bremsstrahlung dose rate up to 10 13 R / s with an average energy of gamma quanta of the order of 2 MeV.

Small-sized pulsed betatrons of the MIB type are used for radiographic quality control of materials and products in non-stationary conditions: at assembly and construction sites, when inspecting welded joints and valves of oil and gas pipelines, inspecting bridge supports and other critical building structures, as well as inspecting casting and welded connections of large thicknesses. The maximum energy of the bremsstrahlung radiation of installations is up to 7.5 MeV, the maximum thickness of material transmission is up to 300 mm.

X-ray sources.

X-ray radiation its physical properties are similar to gamma radiation, but its nature is completely different. This is a low-energy (no more than 100 keV) electromagnetic radiation. It occurs when the atoms of the elements are excited by a stream of electrons, alpha particles or gamma quanta, in which there is an ejection of electrons from the electron shells of the atom. The restoration of the electron shells of the atom is accompanied by the emission of X-ray quanta and has a line spectrum of energies of binding of electrons to the nucleus on the electron shells.

X-ray radiation also accompanies beta decay of radionuclides, in which the nucleus of an element increases its charge by +1, and its electronic shell is restructured. This process makes it possible to create sufficiently powerful and cheap radionuclide sources of X-ray radiation (Table 4). Naturally, such sources are simultaneously sources of certain beta and gamma radiation. For the manufacture of sources, radionuclides with a minimum energy of emitted beta particles and gamma quanta are used.

Table 4. Radionuclide sources of low-energy quanta.

X-ray protection is much simpler than gamma-ray protection. A 1 mm lead layer provides tenfold attenuation of 100 keV radiation.

Physical and technical sources X-ray radiation - X-ray tubes in which radiation is excited in the target (tube anode) under the influence of a stream of electrons accelerated to several tens of keV.

The X-ray tube consists of a glass vacuum cylinder with soldered electrodes - a cathode heated to a high temperature and an anode. The electrons emitted from the cathode are accelerated in the space between the electrodes by a strong electric field (up to 500 kV for powerful tubes) and bombard the anode. When electrons hit the anode, their kinetic energy is partially converted into the energy of characteristic and bremsstrahlung radiation. The efficiency of X-ray tubes usually does not exceed 3%. Since most of the kinetic energy of electrons is converted into heat, the anode is made of a metal with high thermal conductivity, and a target made of a material with a large atomic number, such as tungsten, is applied to its surface (at 45 ° to the electron flow) in the flow focusing zone. For powerful X-ray tubes, forced cooling of the anode (with water or a special solution) is used. The specific power dissipated by the anode in modern tubes is from 10 to 104 W / mm 2.

Fig 3. X-ray tube emission spectrum

A typical radiation spectrum of an X-ray tube is shown in Fig. 3. It consists of a continuous spectrum of electron beam bremsstrahlung and characteristic lines of X-ray radiation (sharp peaks) upon excitation of the inner electron shells of the target atoms.

4. Sources of neutrons.

Neutron radiation is a flux of neutral particles with a mass approximately equal to the mass of a proton. These particles are emitted from the nuclei of atoms in some nuclear reactions, in particular, in the fission reactions of uranium and plutonium nuclei. Due to the fact that neutrons do not have an electric charge, neutron radiation interacts only with the atomic nuclei of the medium and has a sufficiently large penetrating ability. Depending on the kinetic energy (in comparison with the average energy of thermal motion E t ≈ 0.025 eV), neutrons are conventionally divided into thermal (E ~ E t), slow (E t< E < 1 кэВ), промежуточные (1 < E < 500 кэВ) и быстрые (E >500 keV).

The process of attenuation of neutron radiation when passing through a substance consists of the processes of slowing down fast and intermediate neutrons, diffusion of thermal neutrons and their capture by the nuclei of the medium.

In the processes of slowing down fast and intermediate neutrons, the main role is played by the transfer of energy by neutrons to the nuclei of the medium in direct collisions with them (inelastic and elastic scattering). In inelastic scattering, part of the neutron energy is spent on the excitation of the nucleus, which is removed by gamma radiation. In elastic scattering, the less the nuclear mass and the larger the scattering angle, the greater part of its energy is transferred by the neutron to the nucleus. The probability of elastic scattering is practically constant up to energies of 200 keV, and decreases by a factor of 3-5 as the neutron energy increases.

Radiative capture of neutrons is possible on any nucleus, with the exception of helium nuclei. During capture, an excited nucleus is formed, which passes into the ground state with the emission of gamma radiation characteristic of each nuclide, which is widely used for neutron activation analysis of the chemical composition of media with the highest degree of accuracy (up to 10 -8%). Nuclear reactions with the emission of protons and alpha particles are observed on light nuclei. Heavy nuclei in the capture of neutrons are divided into two lighter nuclei with the release of energy up to 200 MeV, of which about 160 MeV is transferred to fission fragments. The capture probability has a dependence on the neutron energy, which is individual for nuclides, with resonance peaks and a decline towards the high-energy region. Neutron capture predominates for slow and thermal neutrons.

Neutron protection is performed from a mixture (layers) of heavy elements (iron, lead for inelastic scattering), light hydrogen and carbon-containing substances (water, paraffin, graphite - elastic scattering), and thermal neutron capture elements (hydrogen, boron). With an average ratio of 1: 4 heavy and light elements, a 10: 100: 1000-fold attenuation of the neutron flux is achieved in layers of approximately 20:32:40 cm.

Of all types of external influences on a person, neutron radiation is the most dangerous, because intensively slows down and is absorbed by the hydrogen-containing environment of the body and causes nuclear reactions in its internal organs.

Radionuclide neutron sources (Table 5) are performed on the basis of excitation in certain chemical elements of nuclear reactions of the type (a, n) - absorption of an alpha particle Þ emission of a neutron, or (g, n) - absorption of a gamma quantum Þ emission of a neutron. They are, as a rule, a homogeneous compressed mixture of an alpha-particles or gamma-ray emitter element and a target element in which a nuclear reaction is initiated. Polonium, radium, plutonium, americium, curium are used as alpha emitters, antimony, yttrium, radium, mesotorium are used as gamma emitters. Elements - targets for alpha emitters - beryllium, boron, for gamma emitters - beryllium, deuterium. The mixture of elements is sealed in stainless steel ampoules.

The most famous ampoule sources are radium-beryllium and polonium-beryllium. Polonium-210 is a near-pure alpha emitter. The decay of polonium is accompanied by low-intensity gamma rays. The main disadvantage is the short service life determined by the half-life of polonium.

The Californium neutron source uses a spontaneous nuclear reaction with the release of a neutron from the nucleus, which is accompanied by strong gamma radiation. With every fission of a nucleus, four neutrons are released. 1 g of a source per second emits 2.4 * 10 12 neutrons, which corresponds to the neutron flux of an average nuclear reactor. The sources have a constant flux of neutrons (no monitoring is required), “point-like” radiation, a long service life (more than three years), and a relatively low cost.

Sources of thermal neutrons are made in a similar way and additionally contain a graphite moderator cover.

Table 5. Radionuclide sources of neutrons.

	Name		Half-time decay, years	energy, MeV	n / 3.7 10 10 Bq
	Polonium, beryllium Plutonium-239, beryllium Plutonium-238, beryllium Radium, beryllium Americium, beryllium Actinium, beryllium Polonius, boron Antimony, beryllium Yttrium, beryllium Mesotorium, beryllium Radium, beryllium Yttrium, deuterium Mesotorium, deuterium Radium, deuterium Californium

The energy spectra of alpha-neutron sources are continuous, from thermal to 6-8 MeV, gamma-neutron - approximately monoenergetic, tens or hundreds of keV. The yield of gamma neutron sources is 1–2 orders of magnitude lower than that of alpha neutron sources, and is accompanied by strong gamma radiation. In alpha neutron sources, the accompanying gamma radiation is usually low-energy and rather weak, with the exception of sources with radium (radiation of radium and its decay products) and americium (low-energy radiation of americium).

Alpha neutron sources are usually limited in use to an interval of 5-10 years, which is caused by the possibility of depressurization of the ampoule when helium accumulates in it and the internal pressure rises.

Physicotechnical source of neutrons is the neutron tube. It is a small-sized electrostatic accelerator of charged particles - deuterons (nuclei of deuterium atoms 2 НºD), which are accelerated to an energy of more than 100 keV, and are directed to thin targets made of deuterium or tritium (3 НºT), in which nuclear reactions are induced:

d + D Þ 3 He + n + 3.3 MeV, d + T Þ 4 He + n + 14.6 MeV.

Most of the released energy is carried away by the neutron. The distribution of neutron energy is rather narrow and practically monoenergetic over the emission angles. The yield of neutrons is of the order of 10 8 per microcoulomb of deuterons. Neutron tubes operate, as a rule, in a pulsed mode, while the output power can exceed 10 12 n / s.

Portable neutron generators have practically no radiation hazard when turned off, they have the ability to regulate the mode of neutron radiation. The disadvantages of generators include a limited service life (100-300 hours) and instability of the neutron yield from pulse to pulse (up to 50%).

5. Inventory and disposal of sources

Radionuclide sources of ionizing radiation pose a potential hazard to the public for the following reasons:

1. They are common in many organizations, and the standard life cycle of sources is not always carried out (acquisition - accounting - control - use - disposal).

2. Sources of ionizing radiation cannot be reliably guarded.

3. The design of sources of ionizing radiation is such that, if handled carelessly or improperly, they can harm human health.

In Russia, on the basis of the Federal State Unitary Enterprise All-Russian Research Institute of Chemical Technology (VNIIKhT) of Rosatom, the Center for State Accounting and Control of Radioactive Substances and Wastes has been established. In 2000-2001, according to the decision of the Government of the Russian Federation, the State inventory of radioactive materials, radioactive waste and sources of ionizing radiation was carried out. Regional departmental information and analytical centers have been created and are functioning. They collect, process and analyze information about the formation, movement, processing and storage of radioactive substances.

The scale and scope of use of radionuclide sources have a tendency to increase, and the problem of the safety of handling sources at all stages of their life cycle has been and will remain one of the most important. Russia has criminal liability for the illegal acquisition, storage, use, transfer or destruction of radioactive materials.

Highly active sources are disposed of at PA Mayak. Low-level sources are disposed of at regional enterprises of NPO Radon.

Radiophobia. Panic fear of any ionizing radiation in any quantity is called radiophobia. It is unreasonable to run out of the room in which the Geiger counter is working and registers the natural radioactive background. You need to understand that about 10 ionizing particles pass through each cm 2 of your skin inside a person every second, and about 10 5 decays per minute occur in the human body.

Radiophobia has now spread to television, as a source of X-ray radiation, and to an aircraft that carries a person to the upper layers of the atmosphere, where the level of cosmic radiation is higher. Television is indeed a source of X-ray radiation, but daily viewing of television programs for three to four hours a day per year will receive a dose 100-200 times less than the natural background. A flight in a modern aircraft over a distance of 2000 km results in approximately one hundredth of the average value of natural exposure per year. There are areas on Earth where the radiation level is hundreds of times higher than the average (up to 250 mSv), but no adverse effects on the health of people living there have been noted.

A decrease in the radiation dose, if it is necessary to work with a source of ionizing radiation, can be carried out in three ways: by increasing the distance from the source, decreasing the time spent near the source, installing a screen that absorbs radiation. With distance from a point source, the radiation dose decreases in inverse proportion to the square of the distance.

All radiation used in medical radiology is divided into two large groups: non-ionizing and ionizing. As the name itself shows, the former, unlike the latter, when interacting with the environment, do not cause ionization of atoms, i.e. decay into oppositely charged particles - ions.

Non-ionizing radiation belongs to thermal (infrared) radiation and resonance, arising in an object (human body), placed in a stable magnetic field, under the influence of high-frequency pulses. In addition, ultrasonic waves, which are elastic vibrations of the medium, are conventionally referred to as non-ionizing radiation.

Ionizing radiation

characterized by the ability to ionize the atoms of the environment, including the atoms that make up human tissues. All these radiations are divided into quantum and corpuscular.

This division is largely arbitrary, since any radiation has a dual nature and, under certain conditions, exhibits either the property of a wave or the property of a particle.

Quantum ionizing radiation includes bremsstrahlung (X-ray) and gamma radiation.

Corpuscular radiation includes beams of electrons, protons, neutrons, mesons.

For medical purposes, the most actively used type of artificial external radiation is X-ray.

X-ray tube

is a vacuum glass vessel, into the ends of which two electrodes are soldered - the cathode and the anode.

The cathode is made in the form of a thin tungsten spiral. When it is heated, a cloud of free electrons is formed around the spiral (thermionic emission). Under the action of a high voltage applied to the poles of the X-ray tube, they are accelerated and focused on the anode. The latter rotates at a tremendous speed (up to 10 thousand rpm), to evenly distribute particles and prevent the anode from melting. As a result of deceleration of electrons at the anode, part of their kinetic energy is converted into electromagnetic radiation.

Another source of ionizing radiation for medical purposes is radioactive nuclides. They are obtained in nuclear reactors using charged particle accelerators, or using radionuclide generators.

Charged particle accelerators

Are installations for obtaining high-energy charged particles using an electric field. Particles move in a vacuum chamber. Their movement is controlled by a magnetic or electric field.

By the nature of the accelerated particles, they distinguish between electron accelerators (betatron, microtron, linear accelerator) and heavy particles - protons, etc. (cyclotron, synchrophasotron).

In diagnostics, accelerators are used to obtain radionuclides, mainly with short and ultrashort half-lives.

In the composition of radiation diagnostics

Includes X-ray diagnostics (roentgenology), radionuclide diagnostics, ultrasound diagnostics, X-ray computed tomography, magnetic resonance imaging, medical thermography (thermal imaging). In addition, it includes the so-called interventional radiology, whose tasks include the implementation of therapeutic interventions based on radiation diagnostic procedures.

The listed methods of radiation diagnostics are based on the study of organs by obtaining their images using various fields and radiation (Medical Imaging). Visualization can be obtained by processing transmitted, emitted or reflected electromagnetic radiation or mechanical vibration (ultrasound).

The following physical phenomena are the basis of modern medical imaging:

- absorption of X-ray radiation in tissues (X-ray diagnostics);

- the emergence of radio frequency radiation during the excitation of unpaired atomic nuclei in a magnetic field (MRI);

- emission of gamma quanta by radionuclides concentrated in certain organs (radionuclide diagnostics);

- reflection towards the sensor of high-frequency beams of directed ultrasonic waves (ultrasound);

- Spontaneous emission of infrared waves by tissues (infrared imaging, thermography).

All of these methods, with the exception of ultrasonic, are based on electromagnetic radiation in various regions of the energy spectrum. Ultrasound imaging is based on capturing vibrations generated by a piezoelectric crystal.

Imaging techniques

can be grouped according to the following criterion: an image of the entire volume of the tissue or its thin layer is obtained. In a conventional X-ray examination, the 3D volume is displayed as a 2D image. A summation image of various organs is obtained on the film. In axial imaging, such as CT, radiation is directed only to a thin layer of tissue. The main advantage of this method is good contrast resolution.

Interaction of ionizing radiation with matter.

Passing through any medium, including human tissue, all ionizing radiation act in almost the same way: they all transfer their energy to the atoms of these tissues, causing them to be excited and ionized.

Protons and especially alpha particles have a large mass, charge and energy. Therefore, they move in the tissues in a straight line, forming dense accumulations of ions. In other words, they have a large linear loss of energy in tissues. The length of their path depends on the initial energy of the particle and the nature of the substance in which it moves.

The electron in tissues has a tortuous range. This is due to its low mass and variability of its direction under the influence of electric fields of atoms. But the electron is able to snatch an orbiting electron from the system of the oncoming atom - to ionize matter. The resulting ion pairs are distributed less densely along the path of the electron than in the case of a proton beam or alpha particles.

Fast neutrons lose their energy mainly as a result of collisions with hydrogen nuclei. These nuclei are ripped out of atoms and themselves create short dense clusters of ions in the tissues. After slowing down, neutrons are captured by atomic nuclei, which can be accompanied by the release of high-energy gamma quanta or high-energy protons, which in turn produce dense clusters of ions. Some of the nuclei, in particular the nuclei of atoms of sodium, phosphorus, chlorine, become radioactive due to interaction with neutrons. Therefore, after irradiation of a person with a flux of neutrons, radionuclides remain in his body, which are a source of radiation (this is a phenomenon of induced radioactivity).

Ionizing is called radiation, which, passing through the medium, causes ionization or excitation of the molecules of the medium. Ionizing radiation, like electromagnetic radiation, is not perceived by the human senses. Therefore, it is especially dangerous, since a person does not know that he is being exposed to it. Ionizing radiation is also called radiation.

Radiation Is a stream of particles (alpha particles, beta particles, neutrons) or very high frequency electromagnetic energy (gamma or X-rays).

Contamination of the working environment with substances that are sources of ionizing radiation is called radioactive contamination.

Nuclear pollution- This is a form of physical (energy) pollution associated with the excess of the natural level of radioactive substances in the environment as a result of human activities.

Substances are made up of the smallest particles of chemical elements - atoms. The atom is divisible and has a complex structure. In the center of an atom of a chemical element is a material particle called an atomic nucleus, around which electrons revolve. Most of the atoms of chemical elements are highly stable, that is, stability. However, in a number of elements known in nature, the nuclei spontaneously disintegrate. Such elements are called radionuclides. One and the same element can have several radionuclides. In this case, they are called radioisotopes chemical element. Spontaneous decay of radionuclides is accompanied by radioactive radiation.

Spontaneous decay of the nuclei of some chemical elements (radionuclides) is called radioactivity.

Radioactive radiation can be of various types: streams of particles with high energy, an electromagnetic wave with a frequency of more than 1.5 .10 17 Hz.

The particles emitted are of various types, but the most commonly emitted are alpha particles (α radiation) and beta particles (β radiation). An alpha particle is heavy and high in energy, it is the nucleus of a helium atom. A beta particle is about 7336 times lighter than an alpha particle, but can also be high in energy. Beta radiation is a stream of electrons or positrons.

Radioactive electromagnetic radiation (it is also called photon radiation), depending on the frequency of the wave, is X-ray (1.5. 10 17 ... 5. 10 19 Hz) and gamma radiation (more than 5. 10 19 Hz). Natural radiation is only gamma radiation. X-ray radiation is artificial and occurs in cathode-ray tubes at voltages of tens and hundreds of thousands of volts.

Radionuclides, emitting particles, are converted into other radionuclides and chemical elements. Radionuclides decay at different rates. The decay rate of radionuclides is called activity... The unit of measurement of activity is the number of decays per unit of time. One decay per second is called becquerel (Bq). Often, another unit is used to measure activity - curie (Ku), 1 Ku = 37.10 9 Bq. One of the first radionuclides studied in detail was radium-226. It was studied for the first time by the Curies, after whom the unit for measuring activity is named. The number of decays per second occurring in 1 gram of radium-226 (activity) is equal to 1 Ku.

The time during which half of the radionuclide decays is called half-life(T 1/2). Each radionuclide has its own half-life. The range of T 1/2 change for various radionuclides is very wide. It varies from seconds to billions of years. For example, the most famous natural radionuclide, uranium-238, has a half-life of about 4.5 billion years.

When decaying, the amount of the radionuclide decreases and its activity decreases. The pattern according to which the activity decreases obeys the law of radioactive decay:

where A 0 - initial activity, A- activity over a period of time t.

Types of ionizing radiation

Ionizing radiation occurs during the operation of devices based on radioactive isotopes, during the operation of electrovacuum devices, displays, etc.

Ionizing radiation includes corpuscular(alpha, beta, neutron) and electromagnetic(gamma, X-ray) radiation, capable of creating charged atoms and ion molecules when interacting with matter.

Alpha radiation is a stream of helium nuclei emitted by matter during radioactive decay of nuclei or during nuclear reactions.

The greater the energy of the particles, the greater the total ionization caused by it in the substance. The range of alpha particles emitted by a radioactive substance reaches 8-9 cm in air, and in living tissue - several tens of microns. Possessing a relatively large mass, alpha particles quickly lose their energy when interacting with matter, which determines their low penetrating ability and high specific ionization, amounting to several tens of thousands of ion pairs in the air per cm of travel.

Beta radiation - the flow of electrons or positrons arising from radioactive decay.

The maximum range of beta particles in air is 1800 cm, and in living tissues - 2.5 cm. The ionizing ability of beta particles is lower (several tens of pairs per 1 cm of range), and the penetrating ability is higher than that of alpha particles.

Neutrons whose flux forms neutron radiation, transform their energy in elastic and inelastic interactions with atomic nuclei.

With inelastic interactions, secondary radiation arises, which can consist of both charged particles and gamma quanta (gamma radiation): with elastic interactions, the usual ionization of matter is possible.

The penetrating power of neutrons largely depends on their energy and the composition of the substance of the atoms with which they interact.

Gamma radiation - electromagnetic (photon) radiation emitted during nuclear transformations or particle interactions.

Gamma radiation has a high penetrating power and low ionizing effect.

X-ray radiation arises in the environment surrounding the source of beta radiation (in X-ray tubes, electron accelerators) and is a combination of bremsstrahlung and characteristic radiation. Bremsstrahlung - photon radiation with a continuous spectrum, emitted when the kinetic energy of charged particles changes; characteristic radiation is photon radiation with a discrete spectrum, emitted when the energy state of atoms changes.

Like gamma radiation, X-ray radiation has a low ionizing capacity and a large penetration depth.

Sources of ionizing radiation

The type of radiation damage to a person depends on the nature of the sources of ionizing radiation.

The natural background radiation consists of cosmic radiation and radiation from naturally distributed radioactive substances.

In addition to natural radiation, a person is exposed to radiation from other sources, for example: during the production of X-ray images of the skull - 0.8-6 R; spine - 1.6-14.7 R; lungs (fluorography) - 0.2-0.5 R: chest with fluoroscopy - 4.7-19.5 R; gastrointestinal tract with fluoroscopy - 12-82 R; teeth - 3-5 R.

A single irradiation of 25-50 rem leads to insignificant transient changes in the blood; at doses of 80-120 rem, signs of radiation sickness appear, but without a lethal outcome. Acute radiation sickness develops with a single irradiation of 200-300 rem, while a lethal outcome is possible in 50% of cases. Death in 100% of cases occurs at doses of 550-700 rem. There are currently a number of anti-radiation drugs available. attenuating the effect of radiation.

Chronic radiation sickness can develop with continuous or repeated irradiation at doses significantly lower than those that cause an acute form. The most characteristic signs of the chronic form of radiation sickness are changes in the blood, disorders of the nervous system, local skin lesions, damage to the lens of the eye, and decreased immunity.

The extent depends on whether the exposure is external or internal. Internal exposure is possible through inhalation, ingestion of radioisotopes and their penetration into the human body through the skin. Some substances are absorbed and accumulated in specific organs, resulting in high localized radiation doses. For example, iodine isotopes accumulating in the body can cause damage to the thyroid gland, rare earth elements - liver tumors, isotopes of cesium, rubidium - soft tissue tumors.

Artificial sources of radiation

In addition to exposure from natural sources of radiation, which were and are always and everywhere, in the 20th century, additional sources of radiation associated with human activities appeared.

First of all, this is the use of X-rays and gamma radiation in medicine in the diagnosis and treatment of patients. obtained with appropriate procedures can be very large, especially in the treatment of malignant tumors with radiation therapy, when directly in the tumor area they can reach 1000 rem and more. During X-ray examinations, the dose depends on the time of the examination and the organ that is diagnosed, and can vary widely - from several rems when taking a picture of a tooth to tens of rems when examining the gastrointestinal tract and lungs. Fluorographic images give the minimum dose, and in no case should you refuse to take preventive annual fluorographic examinations. The average dose that humans receive from medical research is 0.15 rem per year.

In the second half of the 20th century, people began to actively use radiation for peaceful purposes. Various radioisotopes are used in scientific research, in the diagnosis of technical objects, in control and measuring equipment, etc. And, finally, nuclear power. Nuclear power plants are used at nuclear power plants (NPP), icebreakers, ships, submarines. Currently, only at nuclear power plants there are over 400 nuclear reactors with a total electrical power of over 300 million kW. To obtain and process nuclear fuel, a whole complex of enterprises has been created, united in nuclear fuel cycle(NFC).

The nuclear fuel cycle includes enterprises for the extraction of uranium (uranium mines), its enrichment (enrichment factories), the manufacture of fuel cells, the nuclear power plants themselves, enterprises for the secondary processing of spent nuclear fuel (radiochemical plants), for the temporary storage and processing of the generated radioactive waste of the nuclear fuel cycle and, finally, points eternal disposal of radioactive waste (repositories). At all stages of the NFC radioactive substances, to a greater or lesser extent, affect the operating personnel; at all stages, emissions (normal or emergency) of radionuclides into the environment can occur and create an additional dose to the population, especially those living in the area of ​​the NFC enterprises.

Where do radionuclides come from during normal NPP operation? The radiation inside a nuclear reactor is enormous. Fission fragments of fuel, various elementary particles can penetrate through protective shells, microcracks and enter the coolant and air. A number of technological operations in the production of electrical energy at nuclear power plants can lead to water and air pollution. Therefore, nuclear power plants are equipped with a water and gas purification system. Emissions to the atmosphere are carried out through a high chimney.

During normal operation of a nuclear power plant, emissions into the environment are small and have little impact on the population living in the vicinity.

Plants for reprocessing spent nuclear fuel, which has a very high activity, pose the greatest danger from the point of view of radiation safety. These enterprises generate a large amount of liquid waste with high radioactivity, there is a danger of a spontaneous chain reaction (nuclear hazard).

The problem of combating radioactive waste, which is a very significant source of radioactive contamination of the biosphere, is very difficult.

However, the complex and costly radiation at NFC enterprises makes it possible to ensure the protection of humans and the environment to very small values, much less than the existing technogenic background. A different situation occurs when there is a deviation from the normal operating mode, and especially in case of accidents. Thus, the accident that occurred in 1986 (which can be classified as a global catastrophe - the largest accident at nuclear fuel cycle plants in the entire history of nuclear power development) at the Chernobyl nuclear power plant led to the release of only 5% of all fuel into the environment. As a result, radionuclides with a total activity of 50 million Ci were released into the environment. This release led to the irradiation of a large number of people, a large number of deaths, the pollution of very large areas, the need for a massive resettlement of people.

The accident at the Chernobyl nuclear power plant clearly showed that the nuclear method of generating energy is possible only in the event of a fundamental exclusion of large-scale accidents at the NFC enterprises.

Types of ionizing radiation

Ionizing radiation (IR) - flows of elementary particles (electrons, positrons, protons, neutrons) and quanta of electromagnetic energy, the passage of which through a substance leads to ionization (the formation of ions of different polarity) and the excitation of its atoms and molecules. Ionization - the transformation of neutral atoms or molecules into electrically charged particles - ions. IRs fall on the Earth in the form of cosmic rays, arise as a result of radioactive decay of atomic nuclei (απ β-particles, γ– and X-rays), are created artificially at accelerators of charged particles. Of practical interest are the most common types of IR — fluxes of a- and β-particles, γ-radiation, X-rays and neutron fluxes.

Alpha radiation(a) - flux of positively charged particles - helium nuclei. Currently, more than 120 artificial and natural alpha-radioactive nuclei are known, which, emitting an alpha particle, lose 2 protons and 2 neutrons. The particle velocity during decay is 20 thousand km / s. In this case, α-particles have the least penetrating ability, their path length (distance from the source to absorption) in the body is 0.05 mm, in air - 8-10 cm. They cannot even pass through a sheet of paper, but the ionization density per unit the range is very large (by 1 cm to tens of thousands of pairs), therefore these particles have the greatest ionizing ability and are dangerous inside the body.

Beta radiation(β) is the flow of negatively charged particles. Currently, about 900 beta radioactive isotopes are known. The mass of β-particles is several tens of thousands of times less than α-particles, but they have a greater penetrating power. Their speed is 200-300 thousand km / s. The length of the flow from the source in air is 1800 cm, in human tissues - 2.5 cm. Β-particles are completely retained by solid materials (3.5 mm aluminum plate, organic glass); their ionizing capacity is 1000 times less than that of α-particles.

Gamma radiation(γ) - electromagnetic radiation with a wavelength from 1 · 10 -7 m to 1 · 10 -14 m; is emitted during deceleration of fast electrons in matter. It occurs during the decay of most radioactive substances and has a high penetrating power; propagates at the speed of light. In electric and magnetic fields, gamma rays are not deflected. This radiation has a lower ionizing ability than a– and β-radiation, since the ionization density per unit length is very low.

X-ray radiation can be obtained in special X-ray tubes, in electron accelerators, during deceleration of fast electrons in matter and during the transition of electrons from the outer electron shells of the atom to the inner one, when ions are created. X-rays, like γ-radiation, have a low ionizing ability, but a large penetration depth.

Neutrons - elementary particles of the atomic nucleus, their mass is 4 times less than the mass of α-particles. Their lifespan is about 16 minutes. Neutrons have no electrical charge. The path length of slow neutrons in air is about 15 m, in a biological environment - 3 cm; for fast neutrons - respectively 120 m and 10 cm. The latter have a high penetrating power and pose the greatest danger.

There are two types of ionizing radiation:

Corpuscular, consisting of particles with a rest mass other than zero (α-, β- and neutron radiation);

Electromagnetic (γ– and X-ray radiation) - with a very short wavelength.

To assess the impact of ionizing radiation on any substances and living organisms, special values ​​are used - radiation dose. The main characteristic of the interaction of ionizing radiation and the environment is the ionization effect. In the initial period of the development of radiation dosimetry, most often it was necessary to deal with X-rays propagating in the air. Therefore, the degree of air ionization of X-ray tubes or apparatus was used as a quantitative measure of the radiation field. A quantitative measure based on the amount of ionization of dry air at normal atmospheric pressure, which is quite easily measurable, is called the exposure dose.

Exposure dose determines the ionizing capacity of X-rays and γ-rays and expresses the radiation energy converted into kinetic energy of charged particles per unit mass of atmospheric air. The exposure dose is the ratio of the total charge of all ions of the same sign in an elementary volume of air to the mass of air in this volume. In the SI system, the unit for measuring the exposure dose is the pendant divided by the kilogram (C / kg). Non-systemic unit - X-ray (R). 1 C / kg = 3880 R. With the expansion of the range of known types of ionizing radiation and the spheres of its application, it turned out that the measure of the effect of ionizing radiation on a substance does not lend itself to simple determination due to the complexity and diversity of the processes occurring in this case. The most important of them, giving rise to physicochemical changes in the irradiated substance and leading to a certain radiation effect, is the absorption of the energy of ionizing radiation by the substance. As a result of this, the concept of absorbed dose arose.

Absorbed dose shows what amount of radiation energy is absorbed per unit mass of any irradiated substance, and is determined by the ratio of the absorbed energy of ionizing radiation to the mass of the substance. Gray (Gy) is taken as the unit of measurement of the absorbed dose in the SI system. 1 Gy is a dose at which 1 J of ionizing radiation energy is transferred to a mass of 1 kg. The non-systemic unit of the absorbed dose is rad. 1 Gr = 100 glad. The study of individual consequences of irradiation of living tissues showed that at the same absorbed doses, different types of radiation produce different biological effects on the body. This is due to the fact that a heavier particle (for example, a proton) produces more ions per unit path in the tissue than a light one (for example, an electron). At the same absorbed dose, the more dense the ionization created by radiation, the higher the radiobiological destructive effect. To take this effect into account, the concept of an equivalent dose was introduced.

Equivalent dose is calculated by multiplying the value of the absorbed dose by a special coefficient - the coefficient of relative biological effectiveness (RBE) or quality coefficient. The values ​​of the coefficient for various types of radiation are given in table. 7.

Table 7

The coefficient of relative biological effectiveness for various types of radiation

The SI unit of equivalent dose is the sievert (Sv). The value of 1 Sv is equal to the equivalent dose of any type of radiation absorbed in 1 kg of biological tissue and creating the same biological effect as the absorbed dose of 1 Gy of photon radiation. The non-systemic unit of measurement of the equivalent dose is rem (biological equivalent of rad). 1 Sv = 100 rem. Some organs and tissues of a person are more sensitive to the effects of radiation than others: for example, at the same equivalent dose, the occurrence of cancer in the lungs is more likely than in the thyroid gland, and irradiation of the gonads is especially dangerous because of the risk of genetic damage. Therefore, the radiation doses to different organs and tissues should be taken into account with a different coefficient, which is called the radiation risk coefficient. Multiplying the value of the equivalent dose by the corresponding radiation risk factor and summing over all tissues and organs, we obtain effective dose, reflecting the total effect on the body. Weighted coefficients are established empirically and calculated in such a way that their sum for the whole organism is one. The units of measurement for the effective dose are the same as those for the equivalent dose. It is also measured in sievert or rem.