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All ionizing radiations are divided into photon and corpuscular.

Photon-ionizing radiation includes:

• a) Y-radiation emitted during the decay of radioactive isotopes or particle annihilation. Gamma radiation is, by its nature, short-wavelength electromagnetic radiation, i.e. a stream of high-energy quanta of electromagnetic energy, the wavelength of which is much less than the interatomic distances, i.e. y
• b) X-ray radiation that occurs when the kinetic energy of charged particles decreases and / or when the energy state of the electrons of the atom changes.

Corpuscular ionizing radiation consists of a stream of charged particles (alpha, beta particles, protons, electrons), the kinetic energy of which is sufficient to ionize atoms in a collision. Neutrons and other elementary particles do not directly produce ionization, but in the process of interaction with the medium they release charged particles (electrons, protons) that can ionize the atoms and molecules of the medium through which they pass:

a) neutrons - the only uncharged particles formed in some reactions of fission of the nuclei of uranium or plutonium atoms. Since these particles are electrically neutral, they penetrate deeply into any substance, including living tissues. A distinctive feature of neutron radiation is its ability to convert atoms of stable elements into their radioactive isotopes, i.e. create induced radiation, which dramatically increases the danger of neutron radiation. The penetrating power of neutrons is comparable to Y-radiation. Depending on the level of carried energy, fast neutrons (with energies from 0.2 to 20 MeV) and thermal neutrons (from 0.25 to 0.5 MeV) are conditionally distinguished. This difference is taken into account when carrying out protective measures. Fast neutrons are slowed down, losing ionization energy, by substances with a low atomic weight (the so-called hydrogen-containing ones: paraffin, water, plastics, etc.). Thermal neutrons are absorbed by materials containing boron and cadmium (boron steel, boral, boron graphite, cadmium-lead alloy).

Alpha, beta and gamma particles have an energy of only a few megaelectronvolts, and cannot create induced radiation;

• b) beta particles - electrons emitted during the radioactive decay of nuclear elements with an intermediate ionizing and penetrating power (run in air up to 10-20 m).
• c) alpha particles - positively charged nuclei of helium atoms, and in outer space and atoms of other elements, emitted during the radioactive decay of isotopes of heavy elements - uranium or radium. They have a low penetrating ability (run in the air - no more than 10 cm), even human skin is an insurmountable obstacle for them. They are dangerous only when they enter the body, as they are able to knock out electrons from the shell of a neutral atom of any substance, including the human body, and turn it into a positively charged ion with all the ensuing consequences, which will be discussed later. Thus, an alpha particle with an energy of 5 MeV forms 150,000 pairs of ions.

Rice. one

The quantitative content of radioactive material in the human body or substance is defined by the term "radioactive source activity" (radioactivity). The unit of radioactivity in the SI system is the becquerel (Bq), which corresponds to one decay in 1 s. Sometimes in practice the old unit of activity, the curie (Ci), is used. This is the activity of such a quantity of a substance in which 37 billion atoms decay in 1 second. For translation, the following dependence is used: 1 Bq = 2.7 x 10 Ci or 1 Ki = 3.7 x 10 Bq.

Each radionuclide has an invariable, unique half-life (the time required for the substance to lose half of its activity). For example, for uranium-235 it is 4,470 years, while for iodine-131 it is only 8 days.

Electronic accelerators and X-ray machinesand . When passing charged particles in an electromagnetic field with acceleration or deceleration, the energy of the particle is lost in the form of bremsstrahlung photon radiation. This principle is based on the production of photon radiation beams during deceleration of electrons emitted by the X-ray tube cathode and accelerated by the electric field between the cathode and anode on the target.

Figure 5.10 shows a primitive diagram of an X-ray machine that demonstrates what has been said.

Fig.5.10. Primitive scheme of the x-ray apparatus.

The power of such a photon source is determined by the electron current, the voltage between the cathode and the anode, the material and thickness of the target, and is in the range from 10 5 to 10 14 s -1. Approximately, the source power can be expressed by the formula:

J ~ i Z V 2 (5.34),

wherein i- current on the tube, Z is the atomic number of the target material, V- voltage on the tube.

The energy distribution of photons emitted by the target is continuous in the range from 0 to the energy of accelerated electrons and has a form similar to that shown in Fig. 5.11.

Fig.5.11. Energy spectra of X-ray radiation from a tungsten target at various tube voltages.

Against the background of a continuous spectrum of bremsstrahlung, characterized by a maximum photon energy equal to the energy of accelerated electrons, monoenergetic quanta of characteristic radiation of the target material are clearly distinguished, which exceed the amplitude of bremsstrahlung in amplitude, and their position in energy depends on the target material.

The fundamental difference between a linear electron accelerator and an X-ray machine is only in the energy of accelerated electrons, which in X-ray machines usually does not exceed 400 keV, and on accelerators reaches tens MeV. This is also manifested in the bremsstrahlung spectrum, an approximate form of which for electrons is shown in Fig. 5.7. For the practice of calculating the protection against bremsstrahlung of electron accelerators, the often shown spectral distribution is replaced by a monoenergetic one with an effective energy equal to 2/3E e at the energy of accelerated electrons Her<1,7 МэВ ; 1/2 E e at Her in the range 1.7 - 10 MeV, 5 MeV at E e \u003d 10-15 MeV and 1/3 E e at E e >15 MeV.

In addition to the difference in the photon emission spectra of these installations, there is also a difference in the angular distribution of emitted photons (Fig. 5.12).

Fig.5.12. Angular distribution of photons emitted from an accelerator target at different accelerating voltages

On accelerators, photons, as a rule, fly in the direction of the primary electron beam, on an X-ray machine, at low voltages on the tube, in the direction perpendicular to the primary beam.

One more feature of high-energy electron accelerators should be noted. If the energy of bremsstrahlung photon radiation exceeds the binding energy of neutrons in the core of the target material or structural elements, then, according to the reaction (γ,n), powerful accompanying neutron radiation arises, which sometimes determines the radiation situation near the accelerator.

Reactor as a source of photons. The sources of photon radiation in a nuclear reactor differ both in the nature of their formation and in the characteristics of the emitted radiation. The following main groups of reactor photons can be distinguished: prompt gamma radiation, fission product gamma radiation, capture gamma radiation, inelastic neutron scattering gamma radiation, and activation gamma radiation.

Instantaneous gamma radiation represents gamma quanta emitted during the fission of a heavy nucleus and the decay of short-lived fission products, i.e. photon radiation emitted over time t<5·10 -7 с after the fission reaction. The total energy of this gamma radiation is approximately 7 MeV/div, the spectrum of emitted photons decreases with increasing energy and has a continuous energy distribution up to an energy of approximately 7.5 MeV with average photon energy 2.5 MeV. This radiation is generated in the reactor core directly during its operation.

Fission product gamma radiation nuclear fuel is caused by gamma radiation of radionuclides accumulated in the fuel during the operation of the reactor, both directly in the fission process and due to the radioactive decay of these products and the capture of neutrons by the formed fission products. In general, approx. 1000 radionuclides - fission products, each of which has a spectrum of discrete energy lines of gamma rays and its own half-life. The abundance of radionuclides with different decay periods and the presence of many gamma transitions in their decay schemes form an almost continuous spectrum of gamma radiation from fission products, which varies depending on the operating time of the reactor and the time of its shutdowns. Fission product activities at any point in time can be calculated from data on independent or cumulative yields of fission products and cross sections of reactions leading to their formation. After about a year of exposure, the main contribution to the total spectrum is made by photons in the energy range from 0.5 to 0.9 MeV with medium energy 0.8 MeV and a total energy of about 7.5 MeV/div.

Capture gamma radiation occurs when neutrons are captured, both in the fuel material and in the structural elements of the reactor, which leads to the fact that it is formed not only in the reactor core, but also in the structures surrounding it, including the biological protection of the reactor. If, as a first approximation, we assume that in the process of division 235 U formed by thermal neutrons 2,43 neutron/fission, one of which is used for a self-sustaining fission reaction, then approximately 1,43 neutrons are captured with the formation of capture gamma radiation. Taking into account the fact that the cross sections of neutron capture by the structural elements of the reactor have maximum values ​​for neutrons of thermal energies, and the binding energy of neutrons for the nuclei of these materials is in the range 7-11 MeV, then the energy of capture gamma quanta is determined mainly by the neutron binding energy in the nucleus and is equal to 7-11 MeV. This highly penetrating photon radiation in many cases determines the dimensions of the biological protection of the reactor.

Inelastic scattering gamma radiation accompanies the capture of a fast neutron by a nucleus, followed by the emission of a neutron with a lower energy. The difference between the energies of the captured and emitted neutrons is realized by the emission of gamma rays. The dependences of the cross sections of inelastic scattering on the neutron energy have a threshold character; therefore, this process is possible only at neutron energies above approximately 0.8 MeV and heavy materials. Taking into account the low values ​​of the cross sections of inelastic scattering and the low energy of the resulting gamma rays (below 4 MeV), the contribution of this radiation to the characteristics of the gamma radiation field of the reactor is much lower than the contribution of capture gamma radiation.

Activation gamma radiation due to neutron capture reactions by stable nuclei of reactor materials with the formation of radioactive nuclides. This is mainly due to reactions (n,γ) or (n,p). When choosing the structural elements of the reactor, all measures are taken to reduce the concentrations of materials leading to the formation of activation radiation, however, it always occurs as a result of corrosion of materials and the ingress of corrosion products with the primary coolant into the reactor core. The characteristics of the resulting activation radiation radionuclides are well known, since they belong to the radionuclides described above.

It should be noted the features of the formation of gamma radiation fields of the reactor. If the instantaneous, capture, gamma radiation of inelastic neutron scattering and the short-lived activation activity of the coolant of the 1st circuit are formed only during the operation of the reactor, and it is these sources that determine its safe operation, then the gamma radiation of fission products accumulated during the operation of the reactor and long-lived radionuclides of activation radiation determine the gamma radiation of a shutdown reactor, and, consequently, determine the issues of handling spent nuclear fuel and radioactive waste accumulated in the reactor. They also play a decisive role in the radiation environment created in the event of an emergency.

5.4.3. Sources of neutron radiation .

Nuclear reactor as a source of neutrons . Nuclear fission can be carried out under the action of various elementary particles (neutrons, protons, alpha particles, etc.) or photons that carry significant energy. It is mainly heavy nuclei that are subject to fission. Of all the known fission reactions, reactions under the action of neutrons are of the greatest practical importance. One of the conditions for the fission of an excited nucleus, which is formed during the capture of a neutron, is the excess of the excitation energy of a certain threshold - the critical energy E cr, i.e. E + E St> E cr, where E is the kinetic energy of the incident neutron, and E St is the binding energy of the neutron in the nucleus. For isotopes 231 Pa, 232 Th, 237 Np and 238 U, etc. E cr> E St, so their fission requires neutrons with high kinetic energy ( E >1 MeV), or fast neutrons. At the same time for 233 U, 235 U, 239 Pu and 241 Pu E light> E cr. This ratio explains the ability of these isotopes to fission on thermal neutrons; such nuclides are called fissile.

In general, the reaction of neutron capture, the formation of a compound nucleus and the subsequent realization of its excited state, for example, 235 U can be written in the following form:

92 236 U + γ

(absorption without fission -10 – 15%)

92 235 U + 0 1 n 92 236 U

z1 A1 X + z2 A2 Y + γ + β +2.43 0 1 n +ν

(division - 85-90%)

In the fission of heavy nuclei, along with fission fragments z 1 A 1 X , z 2 A 2 Y several secondary neutrons are produced. For example, during the fission of uranium, two new neutrons are more often produced (up to 30%), less often one, three or even four neutrons (up to 25%). In some fission events, secondary neutrons are not produced at all (up to 10%).

An important point determining the possibility of developing a fission chain reaction is the average number of secondary neutrons ν per 1 fission event. Table 5.4 shows the values ​​of ν for the main fissile nuclides during fission by thermal and 238 U fast neutrons.

Ionizing radiation is a combination of various types of microparticles and physical fields that have the ability to ionize a substance, that is, to form electrically charged particles in it - ions.

SECTION III. LIFE SAFETY MANAGEMENT AND ECONOMIC MECHANISMS OF ITS ENSURING

There are several types of ionizing radiation: alpha, beta, gamma, and neutron radiation.

alpha radiation

In the formation of positively charged alpha particles, 2 protons and 2 neutrons, which are part of the helium nuclei, take part. Alpha particles are formed during the decay of the nucleus of an atom and can have an initial kinetic energy from 1.8 to 15 MeV. Characteristic features of alpha radiation are high ionizing and low penetrating power. When moving, alpha particles lose their energy very quickly, and this causes the fact that it is not enough even to overcome thin plastic surfaces. In general, external exposure to alpha particles, if we do not take into account high-energy alpha particles obtained using an accelerator, does not cause any harm to humans, but the penetration of particles into the body can be hazardous to health, since alpha radionuclides have a long half-life and are highly ionized. If ingested, alpha particles can often be even more dangerous than beta and gamma radiation.

beta radiation

Charged beta particles, whose speed is close to the speed of light, are formed as a result of beta decay. Beta rays are more penetrating than alpha rays - they can cause chemical reactions, luminescence, ionize gases, and have an effect on photographic plates. As a protection against the flow of charged beta particles (energy no more than 1 MeV), it will be enough to use an ordinary aluminum plate 3-5 mm thick.

Photon radiation: gamma radiation and x-rays

Photon radiation includes two types of radiation: x-ray (can be bremsstrahlung and characteristic) and gamma radiation.

The most common type of photon radiation is very high energy at ultrashort wavelength gamma particles, which are a stream of high energy, chargeless photons. Unlike alpha and beta rays, gamma particles are not deflected by magnetic and electric fields and have a much greater penetrating power. In certain quantities and for a certain duration of exposure, gamma radiation can cause radiation sickness and lead to various oncological diseases. Only such heavy chemical elements as, for example, lead, depleted uranium and tungsten can prevent the propagation of the flow of gamma particles.

neutron radiation

The source of neutron radiation can be nuclear explosions, nuclear reactors, laboratory and industrial installations.

Neutrons themselves are electrically neutral, unstable (the half-life of a free neutron is about 10 minutes) particles, which, due to the fact that they have no charge, are characterized by high penetrating power with a low degree of interaction with matter. Neutron radiation is very dangerous, therefore, a number of special, mainly hydrogen-containing, materials are used to protect against it. Best of all, neutron radiation is absorbed by ordinary water, polyethylene, paraffin, and solutions of heavy metal hydroxides.

How do ionizing radiations affect substances?

All types of ionizing radiation to some extent affect various substances, but it is most pronounced in gamma particles and neutrons. So, with prolonged exposure, they can significantly change the properties of various materials, change the chemical composition of substances, ionize dielectrics and have a destructive effect on biological tissues. The natural radiation background will not bring much harm to a person, however, when handling artificial sources of ionizing radiation, one should be very careful and take all necessary measures to minimize the level of exposure to radiation on the body.

Types of ionizing radiation and their properties

Ionizing radiation is a stream of particles and electromagnetic quanta, as a result of which differently charged ions are formed on the medium.

Different types of radiation are accompanied by the release of a certain amount of energy and have different penetrating power, so they have different effects on the body. The greatest danger to humans is radioactive radiation, such as y-, X-ray, neutron, a- and b-radiation.

X-ray and y-radiation are flows of quantum energy. Gamma rays have shorter wavelengths than x-rays. By their nature and properties, these radiations differ little from each other, they have a high penetrating power, straightness of propagation and the ability to create secondary and scattered radiation in the media through which they pass. However, while X-rays are usually produced electronically, y-rays are emitted by unstable or radioactive isotopes.

The remaining types of ionizing radiation are fast-moving particles of matter (atom), some of which carry an electric charge, others do not.

Neutrons are the only uncharged particles produced by any radioactive transformation, with a mass equal to that of a proton. Since these particles are electrically neutral, they penetrate deeply into any substance, including living tissues. Neutrons are the basic particles from which the nuclei of atoms are built.

When passing through matter, they interact only with the nuclei of atoms, transfer part of their energy to them, and themselves change the direction of their movement. The nuclei of atoms "jump out" from the electron shell and, passing through the substance, produce ionization.

Electrons are light negatively charged particles that exist in all stable atoms. Electrons are very often used during the radioactive decay of matter, and then they are called β-particles. They can also be obtained in the laboratory. The energy lost by electrons when passing through matter is spent on excitation and ionization, as well as on the formation of bremsstrahlung.

Alpha particles are the nuclei of helium atoms, devoid of orbital electrons and consisting of two protons and two neutrons linked together. They have a positive charge, are relatively heavy, and as they pass through the substance, they produce ionization of a substance of high density.

Usually a-particles are emitted during the radioactive decay of natural heavy elements (radium, thorium, uranium, polonium, etc.).

Charged particles (electrons and nuclei of helium atoms), passing through the substance, interact with the electrons of atoms, losing 35 and 34 eV, respectively. In this case, one half of the energy is spent on ionization (separation of an electron from an atom), and the other half on the excitation of atoms and molecules of the medium (transfer of an electron to a shell more remote from the nucleus).

The number of ionized and excited atoms formed by an a-particle per unit path length in a medium is hundreds of times greater than that of a p-particle (Table 5.1).

Table 5.1. The range of a- and b-particles of different energies in muscle tissue

This is due to the fact that the mass of an a-particle is about 7000 times greater than the mass of a beta-particle, therefore, at the same energy, its speed is much less than that of a beta-particle.

The α-particles emitted during radioactive decay have a speed of approximately 20 thousand km/s, while the speed of β-particles is close to the speed of light and amounts to 200...270 thousand km/s. It is obvious that the lower the speed of the particle, the greater the probability of its interaction with the atoms of the medium, and, consequently, the greater the energy loss per unit path in the medium, which means the lower the range. From Table. 5.1 it follows that the range of a-particles in muscle tissue is 1000 times less than the range of β-particles of the same energy.

When ionizing radiation passes through living organisms, it transfers its energy to biological tissues and cells unevenly. As a result, despite the small amount of energy absorbed by tissues, some cells of living matter will be significantly damaged. The total effect of ionizing radiation localized in cells and tissues is presented in Table. 5.2.

Table 5.2. Biological effect of ionizing radiation

Primary radiation-chemical changes in molecules can be based on two mechanisms: 1) direct action, when a given molecule undergoes changes (ionization, excitation) directly upon interaction with radiation; 2) indirect action, when the molecule does not directly absorb the energy of ionizing radiation, but receives it by transferring it from another molecule.

It is known that in biological tissue 60...70% of the mass is water. Therefore, let us consider the difference between the direct and indirect effects of radiation using the example of irradiation of water.

Let us assume that a water molecule is ionized by a charged particle, as a result of which it loses an electron:

H2O -> H20+e - .

An ionized water molecule reacts with another neutral water molecule, resulting in the formation of a highly reactive OH hydroxyl radical:

H2O + H2O -> H3O + + OH *.

The ejected electron also very quickly transfers energy to the surrounding water molecules, and in this case, a highly excited water molecule H2O* arises, which dissociates to form two radicals, H* and OH*:

H2O + e- -> H2O*H' + OH'.

Free radicals contain unpaired electrons and are extremely reactive. Their life time in water is no more than 10-5 s. During this time, they either recombine with each other or react with the dissolved substrate.

In the presence of oxygen dissolved in water, other radiolysis products are also formed: the free radical of hydroperoxide HO2, hydrogen peroxide H2O2 and atomic oxygen:

H * + O2 -> HO2;
HO*2 + HO2 -> H2O2 +20.

In a cell of a living organism, the situation is much more complicated than in the case of water irradiation, especially if the absorbing substance is large and multicomponent biological molecules. In this case, organic radicals D* are formed, which are also characterized by extremely high reactivity. With a large amount of energy, they can easily lead to the breaking of chemical bonds. It is this process that occurs most often in the interval between the formation of ion pairs and the formation of final chemical products.

In addition, the biological effect is enhanced by the influence of oxygen. The highly reactive product DO2* (D* + O2 -> DO2*), which is also formed as a result of the interaction of a free radical with oxygen, leads to the formation of new molecules in the irradiated system.

The free radicals and oxidant molecules produced in the process of water radiolysis, having high chemical activity, enter into chemical reactions with protein molecules, enzymes and other structural elements of biological tissue, which leads to a change in biological processes in the body. As a result, metabolic processes are disturbed, the activity of enzyme systems is suppressed, tissue growth slows down and stops, new chemical compounds appear that are not characteristic of the body - toxins. This leads to disruption of the vital activity of individual systems or the organism as a whole.

Chemical reactions induced by free radicals involve many hundreds and thousands of molecules that are not affected by radiation. This is the specificity of the action of ionizing radiation on biological objects. No other type of energy (thermal, electrical, etc.), absorbed by a biological object in the same amount, leads to such changes as ionizing radiation causes.

Undesirable radiation effects of exposure to radiation on the human body are conditionally divided into somatic (soma - Greek for "body") and genetic (hereditary).

Somatic effects are manifested directly in the irradiated person himself, and genetic ones in his offspring.

Over the past decades, a large number of artificial radionuclides have been created by man, the use of which is an additional burden on the natural radiation background of the Earth and increases the radiation dose to people. But, aimed exclusively at peaceful use, ionizing radiation is useful for humans, and today it is difficult to indicate a field of knowledge or the national economy that does not use radionuclides or other sources of ionizing radiation. By the beginning of the 21st century, the "peaceful atom" has found its application in medicine, industry, agriculture, microbiology, energy, space exploration and other areas.

Types of radiation and interaction of ionizing radiation with matter

The use of nuclear energy has become a vital necessity for the existence of modern civilization and, at the same time, a huge responsibility, since it is necessary to use this source of energy as rationally and carefully as possible.

A useful feature of radionuclides

Due to radioactive decay, the radionuclide "gives a signal", thereby determining its location. Using special devices that record the signal from the decay of even single atoms, scientists have learned to use these substances as indicators to help investigate a variety of chemical and biological processes taking place in tissues and cells.

Types of technogenic sources of ionizing radiation

All man-made sources of ionizing radiation can be divided into two types.

• Medical - used both for diagnosing diseases (for example, x-ray and fluorography machines) and for conducting radiotherapy procedures (for example, radiotherapy units for cancer treatment). Also, medical sources of AI include radiopharmaceuticals (radioactive isotopes or their compounds with various inorganic or organic substances), which can be used both to diagnose diseases and to treat them.
• Industrial - man-made radionuclides and generators:
  • in the energy sector (reactors of nuclear power plants);
  • in agriculture (for selection and research on the effectiveness of fertilizers)
  • in the defense sphere (fuel for nuclear-powered ships);
  • in construction (non-destructive testing of metal structures).

According to static data, the volume of production of radionuclide products in the world market in 2011 amounted to 12 billion dollars, and by 2030 this figure is expected to increase sixfold.

Ionizing Radiation (IR) – This is radiation, the interaction of which with a medium leads to the formation of ions of different signs in this medium. Radiation is considered ionizing if it is capable of breaking the chemical bonds of molecules. Ionizing radiation is divided into corpuscular and photon.

Radio waves, light waves, thermal energy of the Sun do not belong to ionizing radiation, since they do not cause damage to the body through ionization.

Corpuscular - this is a stream of particles with a mass other than zero (electrons, protons, neutrons, alpha particles).

Photon- this is electromagnetic radiation, indirectly ionizing radiation (gamma radiation, characteristic radiation, bremsstrahlung, x-rays, annihilation radiation).

alpha radiation- this is a stream of alpha particles (nuclei of helium atoms) emitted during radioactive decay, as well as during nuclear reactions and transformations. Alpha particles have a strong ionizing power and little penetrating power. In the air, they penetrate to a depth of several centimeters, in biological tissue - to a depth of a fraction of a millimeter, and are retained by a sheet of paper, fabric of clothing. Alpha radiation is especially dangerous when its source enters the body with food or inhaled air.

beta radiation is the flow of electrons or positrons emitted by the nuclei of radioactive elements during beta decay. Their ionizing ability is less than that of alpha particles, but their penetrating power is many times greater, and amounts to tens of centimeters. In biological tissue, they penetrate to a depth of 2 cm, only partially retained by clothing. Beta radiation is dangerous to human health, both with external and internal exposure.

proton radiation- this is the flow of protons that form the basis of cosmic radiation, as well as those observed during nuclear explosions. Their range in air and penetrating power are intermediate between alpha and beta radiation.

neutron radiation- the flux of neutrons observed in nuclear explosions, especially neutron munitions and the operation of a nuclear reactor. The consequences of its impact on the environment depend on the initial neutron energy, which can vary within 0.025-300 MeV.

Gamma radiation- electromagnetic radiation (wavelength 10 -10 -10 -14 m), which occurs in some cases during alpha and beta decay, particle annihilation and excitation of atoms and their nuclei, deceleration of particles in an electric field. The penetrating power of gamma radiation is much greater than that of the above types of radiation. The depth of propagation of gamma rays in the air can reach hundreds and thousands of meters. The ionizing ability (indirect) is much less than that of the above types of radiation. Most gamma quanta pass through biological tissue, and only a small amount is absorbed by the human body.

Bremsstrahlung- photon radiation with a continuous energy spectrum, emitted with a decrease in the kinetic energy of charged particles. The environmental impact is the same as gamma radiation.

Characteristic radiation- photon radiation with a discrete energy spectrum, which occurs when the energy state of the electrons of the atom changes. The impact on biological tissue is similar to gamma radiation.

annihilation radiation– photon radiation resulting from the annihilation of a particle and an antiparticle (for example, a positron and an electron). The impact on biological tissue is similar to gamma radiation.

Photon IRs include radiation from radioactive substances, characteristic and bremsstrahlung generated by various accelerators. The LPI of photon radiation is the lowest (1-2 pairs of ions per 1 cm 3 of air), which determines its high penetrating ability (the path length in air is several hundred meters).

-radiation occurs during radioactive decay. The transition of the nucleus from the excited to the ground state is accompanied by the emission of a -quantum with energies from 10 keV to 5 MeV. The main therapeutic sources - radiation are - devices (guns).

Bremsstrahlung X-ray arises due to the acceleration and sharp deceleration of electrons in vacuum systems of various accelerators and differs from X-ray by a higher photon energy (from one to tens of MeV).

When a photon flux passes through a substance, it is weakened as a result of the following interaction processes (the type of interaction of photons with atoms of a substance depends on the photon energy):

Classical (coherent or Thompson scattering) - for photons with energy from 10 to 50-100 keV. The relative frequency of this effect is small. An interaction takes place, which does not play a significant role, since the incident quantum, colliding with an electron, is deflected, and its energy does not change.

Photoelectric absorption (photoelectric effect) - at relatively low energies - from 50 to 300 keV (plays a significant role in X-ray therapy). The incident quantum knocks out an orbital electron from the atom, is itself absorbed, and the electron, having slightly changed direction, flies away. This escaped electron is called a photoelectron. Thus, the energy of a photon is spent on the work function of the electron and on giving it kinetic energy.

Compton effect (incoherent scattering) - occurs at a photon energy from 120 keV to 20 MeV (i.e., almost the entire spectrum of radiation therapy). The incident quantum knocks out an electron from the outer shell of the atom, transferring part of the energy to it, and changes its direction. The electron flies out of the atom at a certain angle, and the new quantum differs from the original one not only in a different direction of motion, but also in lower energy. The resulting quantum will indirectly ionize the medium, and the electron - directly.

The process of formation of electron-positron pairs - the quantum energy must be greater than 1.02 MeV (twice the rest energy of the electron). This mechanism has to be taken into account when a patient is irradiated with a beam of high-energy bremsstrahlung, i.e., on high-energy linear accelerators. Near the nucleus of an atom, the incident quantum experiences acceleration and disappears, transforming into an electron and a positron. A positron quickly combines with an oncoming electron, and the process of annihilation (mutual annihilation) occurs, and instead two photons appear, the energy of each of which is half the energy of the original photon. Thus, the energy of the primary quantum is converted into the kinetic energy of the electron and into the energy of the annihilation radiation.

A photo nuclear takeover - the quantum energy must be more than 2.5 MeV. A photon is absorbed by the nucleus of an atom, as a result of which the nucleus passes into an excited state and can either give up an electron or fall apart. This is how neutrons are produced.

As a result of the above processes of interaction of photon radiation with matter, secondary photon and corpuscular radiation (electrons and positrons) arises. The ionization ability of particles is much greater than that of photon radiation.

The spatial attenuation of the photon beam occurs according to an exponential law (the inverse square law): the radiation intensity is inversely proportional to the square of the distance to the radiation source.

Radiation in the energy range from 200 keV to 15 MeV has found the widest application in the treatment of malignant neoplasms. Great penetrating power allows you to transfer energy to deeply located tumors. This sharply reduces the radiation exposure to the skin and subcutaneous tissue, which allows you to bring the required dose to the lesion without radiation damage to these areas of the body (unlike soft x-rays). With an increase in photon energy above 15 MeV, the risk of radiation damage to tissues at the exit from the beam increases.

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