Ionizing radiation contains ultraviolet rays. Passage of radiation and ionizing radiation through obstacles
All radiations used in medical radiology are divided into two large groups: non-ionizing and ionizing. decay into oppositely charged particles called ions.
Among non-ionizing radiation belongs to thermal (infrared) radiation and resonant radiation that occurs in an object (human body) placed in a stable magnetic field under the action of high-frequency pulses. In addition, ultrasonic waves, which are elastic vibrations of the medium, are conditionally referred to as non-ionizing radiation.
ionizing radiation
characterized by the ability to ionize atoms 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, at the ends of which two electrodes are soldered - a cathode and an 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 revolutions per minute), for uniform distribution of particles and prevention of anode melting. As a result of the deceleration of electrons at the anode, some of them kinetic energy turns into electromagnetic radiation.
Another source of ionizing radiation for medical purposes is radioactive nuclides. They are produced in nuclear reactors at charged particle accelerators, or with the help of radionuclide generators.
particle accelerators
- these 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 field or electric.
According to the nature of the accelerated particles, they distinguish between accelerators of electrons (betatron, microtron, linear accelerator) and heavy particles - protons, etc. (cyclotron, synchrophasotron).
In diagnostics, accelerators are used to produce radionuclides, predominantly with short and ultrashort half-lives.
As part of radiodiagnosis
includes X-ray diagnostics (radiology), 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 medical 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).
Modern medical imaging is based on the following physical phenomena:
- absorption in the tissues of X-ray radiation (X-ray diagnostics);
- the occurrence of radio frequency radiation during the excitation of unpaired nuclei of atoms in a magnetic field (MRI);
— emission of gamma rays by radionuclides concentrated in certain organs (radionuclide diagnostics);
- reflection towards the sensor of high-frequency rays of directed ultrasonic waves (ultrasound);
- spontaneous emission of infrared waves by tissues (infrared imaging, thermography).
All 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 methods
can also be grouped according to the following feature: an image of the entire volume of the tissue or its thin layer is obtained. In a conventional x-ray examination, a three-dimensional volume is displayed as a two-dimensional image. A sum image is obtained on the film various bodies. In axial imaging, such as CT, radiation is directed only at thin layer fabrics. Main advantage this method is a good contrast resolution.
Interaction of ionizing radiation with matter.
Passing through any medium, including human tissues, all ionizing radiations act in almost the same way: they all transfer their energy to the atoms of these tissues, causing their excitation and ionization.
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 energy loss 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.
An electron in tissues has a tortuous path. This is due to its low mass and the variability of its direction under the action of the electric fields of atoms. But an electron is able to pull out an orbital electron from the system of an oncoming atom - to produce ionization of matter. The resulting pairs of ions are distributed along the path of the electron less densely 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 break out of the atoms and themselves create short dense clusters of ions in the tissues. After moderation, neutrons are captured by atomic nuclei, which can be accompanied by the release of high-energy gamma rays or high-energy protons, which in turn give rise to dense clusters of ions. Some of the nuclei, in particular the nuclei of sodium, phosphorus, and chlorine atoms, become radioactive due to interaction with neutrons. Therefore, after irradiating a person with a neutron flux, radionuclides remain in his body, which are a source of radiation (this is the phenomenon of induced radioactivity).
ionizing radiation- streams of photons, as well as charged or neutral particles, the interaction of which with the substance of the medium leads to its ionization. Ionization plays an important role in the development of radiation-induced effects, especially in living tissue. The average energy consumption for the formation of one pair of ions depends relatively little on the type ionizing radiation, which makes it possible to judge by the degree of ionization of a substance about the energy transferred to it I. and. For registration and analysis ionizing radiation instrumental methods also use ionization.
Sources ionizing radiation divided into natural (natural) and artificial. natural sources ionizing radiation are space and radioactive substances common in nature (radionuclides). In space, cosmic radiation is formed and reaches the Earth - corpuscular streams of ionizing radiation. Primary cosmic radiation consists of charged particles and high-energy photons. In the Earth's atmosphere, primary cosmic radiation is partially absorbed and initiates nuclear reactions, which result in the formation of radioactive atoms that themselves emit radiation. , so the cosmic radiation near the Earth's surface differs from the primary cosmic radiation. There are three main types of cosmic radiation: galactic cosmic radiation, solar cosmic radiation, and the Earth's radiation belts. Galactic cosmic radiation is the most high-energy component of the corpuscular flow in interplanetary space and represents the nuclei of chemical elements (mainly hydrogen and helium), accelerated to high energies; in its penetrating ability, this type of cosmic radiation surpasses all types ionizing radiation except for neutrinos. Complete absorption of galactic cosmic radiation would require a lead shield about 15 m. Solar cosmic radiation is a high-energy part of the solar corpuscular radiation and occurs during chromospheric flares during the day. During the period of intensive solar flares the flux density of solar cosmic radiation can be thousands of times higher than the usual level of flux density of galactic cosmic radiation. Solar cosmic radiation consists of protons, helium nuclei and heavier nuclei. Solar high-energy protons pose the greatest danger to humans during space flight (see. Space biology and medicine). The Earth's radiation belts were formed in near-Earth space due to primary cosmic radiation and partial capture of its charged component by the Earth's magnetic field. The Earth's radiation belts consist of charged particles: electrons in the electron belt and protons in the proton belt. In radiation belts the field And is established. increased intensity, which is taken into account when launching manned spacecraft.
Natural, or natural, radionuclides are of various origins; some of them belong to radioactive families, the ancestors of which (uranium, thorium) have been part of the rocks that make up our planet since the period of its formation; some part of natural radionuclides is a product of activation of stable isotopes by cosmic radiation. A distinctive property of radionuclides is radioactivity, i.e. spontaneous transformation (decay) of atomic nuclei, leading to a change in their atomic number and (or) mass number. The rate of radioactive decay, which characterizes the activity of a radionuclide, is equal to the number of radioactive transformations per unit of time.
The International System of Units (SI) defines the becquerel as the unit of radioactivity ( Bq); 1 Bq is equal to one decay per second. In practice, the off-system unit of curie activity is also used ( Key); 1 Key is equal to 3.7 × 10 10 disintegrations per second, i.e. 3.7×10 10 Bq. As a result of radioactive transformations, charged and neutral particles arise, which form the field of radiation.
According to the type of particles that make up ionizing radiation, distinguish between alpha radiation, beta radiation, gamma radiation, X-ray radiation, neutron radiation, proton radiation, etc. X-ray and gamma radiation are classified as photon, or electromagnetic, ionizing radiation, and all other types ionizing radiation- to corpuscular. Photons are "portions" (quanta) of electromagnetic radiation. Their energy is expressed in electron volts. It is tens of thousands of times greater than the energy of visible light quantum.
Alpha radiation is a stream of alpha particles, or nuclei of helium atoms, carrying a positive charge equal to two elementary units of charge. Alpha particles are highly ionizing particles that quickly lose their energy when interacting with matter. For this reason, alpha radiation is weakly penetrating and is used in medical practice either to irradiate the surface of the body, or an alpha-emitting radionuclide is injected directly into the pathological focus during interstitial radiation therapy.
Beta radiation - a stream of negatively charged electrons or positively charged positrons emitted during beta decay. Beta particles are weakly ionizing particles; however, compared to alpha particles at the same energy, they have a greater penetrating power.
Neutron radiation is a stream of electrically neutral particles (neutrons) that arise in some nuclear reactions during the interaction of high-energy elementary particles with matter, as well as during the fission of heavy nuclei. Neutrons transfer part of their energy to the nuclei of atoms of the matter of the medium and initiate nuclear reactions. As a result, charged particles of various types appear in the matter irradiated by the neutron flux, which ionize the matter of the medium, and radionuclides can also be formed. The properties of neutron radiation and the nature of its interaction with living tissue are determined by the neutron energy.
Some species ionizing radiation arise in nuclear power and nuclear physics installations; nuclear reactors, particle accelerators, x-ray machines, and artificial radionuclides created with the help of these tools.
proton radiation is generated in special accelerators. The eye is a stream of protons - particles that carry a unit positive charge and have a mass close to the mass of neutrons. Protons are highly ionizing particles; being accelerated to high energies, they are able to penetrate relatively deeply into the matter of the medium. This makes it possible to efficiently use proton radiation in remote control. radiotherapy.
Electron radiation is generated by special electron accelerators (for example, betatrons, linear accelerators) if a beam of accelerated electrons is brought out. The same accelerators can be a source of bremsstrahlung - a type of photon radiation that occurs when accelerated electrons decelerate in the material of a special accelerator target. The X-ray radiation used in medical radiology is also the bremsstrahlung of electrons accelerated in an X-ray tube.
Gamma radiation - a stream of high-energy photons emitted during the decay of radionuclides; widely used in radiation therapy of malignant neoplasms. Distinguish directed and undirected I. and. If all directions of propagation ionizing radiation are equivalent, then they speak of isotropic I. and. On character of distribution in time I. and. can be continuous and pulsed.
For the description of the field I. and. use physical quantities, which determine the spatiotemporal distribution of radiation in the matter of the medium. The most important characteristics fields I. and. are the particle flux density and the energy flux density. In the general case, the particle flux density is the number of particles penetrating an elementary sphere per unit time, divided by the cross-sectional area of this sphere. Energy flux density I. and. is a synonym for the term "radiation intensity" common in practice. It is equal to the particle flux density multiplied by the average energy of one particle and characterizes the rate of energy transfer I. and. Unit of measurements of intensity And. and. in the SI system is J/m 2 × s.
Biological effect of ionizing radiation. Under biological action And. and. understand the diverse reactions that occur in an irradiated biological object, ranging from the primary processes of radiation energy exchange to effects that manifest themselves long after exposure to radiation. Knowledge of mechanisms biological actionionizing radiation necessary for the urgent adoption of adequate measures to ensure the radiation safety of personnel and the public in case of accidents at nuclear power plants and other enterprises of the nuclear industry. For the ionization of most of the elements that make up the biological substrate, a fairly large amount of energy is needed - 10-15 eV called the ionization potential. Because particles and photons ionizing radiation have energy from tens to millions eV, which far exceeds the energy of intra- and intermolecular bonds of molecules and substances that make up any biological substrate, then all living things are subject to damaging radiation effects.
The most simplified scheme initial stages radiation injury is as follows. Following and essentially simultaneously with the transfer of energy I. and. atoms and molecules of the irradiated medium (the physical stage of the biological action of I. and.), primary radiation-chemical processes develop in it, which are based on two mechanisms: direct, when the molecules of a substance experience changes during direct interaction with ionizing radiation, and indirect, in which the modified molecules do not directly absorb energy ionizing radiation, and receive it by transfer from other molecules. As a result of these processes, free radicals and other highly reactive products are formed, leading to a change in vital macromolecules, and in the final - to the final biological effect. In the presence of oxygen, radiation-chemical processes are intensified (oxygen effect), which, ceteris paribus, enhances the biological action of I. and. (cm. radio modification, Radio modifying agents). It should be borne in mind that changes in the irradiated substrate are not necessarily final and irreversible. As a rule, the final result in each particular case cannot be predicted, because along with radiation damage, restoration of the initial state can also occur.
Impact ionizing radiation on a living organism is commonly called irradiation, although this is not entirely accurate, because the irradiation of the body can also be carried out by any other type of non-ionizing radiation (visible light, infrared, ultraviolet, high-frequency radiation, etc.). The effectiveness of irradiation depends on the time factor, which is understood as the distribution doses of ionizing radiation in time. Single acute irradiation is most effective at high dose rate And. and. Prolonged chronic or intermittent (fractionated) irradiation at a given dose has a lower biological effect, due to the processes post-radiation recovery.
Distinguish between external and internal radiation. At external radiation source And. and. is located outside the body, and with the internal (incorporated) it is carried out by radionuclides that enter the body through the respiratory system, gastrointestinal tract or through damaged skin.
Biological action ionizing radiation largely depends on its quality, which is mainly determined by linear energy transfer (LET) - the energy lost by a particle per unit length of its path in the substance of the medium. Depending on the LET value, all ionizing radiation divided into rare ionizing (LET less than 10 keV/µm) and densely ionizing (LET over 10 keV/µm). Impact different typesionizing radiation in equal absorbed doses leads to effects of different magnitude. For a quantitative assessment of the quality of radiation, the concept of relative biological effectiveness (RBE) has been introduced, which is usually evaluated by comparing the dose of the studied I. and. , causing a certain biological effect, with a dose of standard And. and. , causing the same effect. It can be conditionally considered that the RBE depends only on the LET and increases with an increase in the latter.
At whatever level - tissue, organ, systemic or organismic, the biological action of I. and. , its effect is always determined by the action of I. and. at the cell level. Detailed study of reactions initiated in the cell ionizing radiation, constitutes the subject fundamental research radiobiology. It should be noted that most of the reactions excited ionizing radiation, including such a universal reaction as a delay in cell division, is temporary, transient and does not affect the viability of the irradiated cell. Reactions of this type - reversible reactions - also include various metabolic disorders, incl. inhibition of nucleic acid metabolism and oxidative phosphorylation, adhesion of chromosomes, etc. The reversibility of this type of radiation reactions is explained by the fact that they are the result of damage to a part of multiple structures, the loss of which is very quickly replenished or simply goes unnoticed. From here and characteristic feature of these reactions: with increase in a dose And. and. it is not the proportion of reacting individuals (cells) that increases, but the magnitude, the degree of reaction (for example, the duration of the delay in division) of each irradiated cell.
Significantly different nature are the effects that lead the irradiated cell to death - lethal radiation reactions. In radiobiology, cell death is understood as the loss of a cell's ability to divide. On the contrary, “survivors” are those cells that have retained the ability to reproduce (clone).
There are two forms of lethal reactions that are fatal for dividing and poorly differentiated cells: interphase, in which the cell dies shortly after irradiation, at least before the onset of the first mitosis, and reproductive, when the affected cell does not die immediately after exposure to radiation. , but in the process of division. The most common reproductive form of lethal reactions. The main cause of cell death in it is the structural damage to chromosomes that occurs under the influence of irradiation. These lesions are easily detected by cytological examination of cells on different stages mitosis and have the appearance of chromosomal rearrangements, or chromosomal aberrations. Due to the incorrect connection of chromosomes and the simple loss of their terminal fragments during division, the descendants of such a damaged cell will undoubtedly die immediately after this division or as a result of two or three subsequent mitoses (depending on the significance of the lost genetic material for cell viability). The occurrence of structural damage to chromosomes is a probability process, mainly associated with the formation of double breaks in the DNA molecule, i.e. with irreparable damage to vital cellular macromolecules. In this regard, unlike the reversible cellular reactions considered above, with increase in a dose And. and. the number (proportion) of cells with lethal genome damage increases, which is strictly described for each type of cell in the “dose-effect” coordinates. Currently, special methods have been developed for isolating clonogenic cells from various tissues in vivo and growing them in vitro, with the help of which, after constructing the appropriate dose survival curves, the radiosensitivity of the studied organs and the possibility of its change in the desired direction are quantified. In addition, counting the number of cells with chromosomal aberrations on special preparations is used for biological dosimetry to assess the radiation situation, for example, on board spaceship, as well as to determine the severity and prognosis of acute radiation sickness.
The described radiation reactions of cells underlie the immediate effects that manifest themselves in the first hours, days, weeks and months after the general irradiation of the body or local irradiation of individual segments of the body. These include, for example, erythema, radiation dermatitis, various manifestations of acute radiation sickness (leukopenia, bone marrow aplasia, hemorrhagic syndrome, intestinal lesions), sterility (temporary or permanent, depending on the dose ionizing radiation).
After a long time (months and years) after exposure, long-term consequences of local and general radiation exposure develop. These include reduced life expectancy, the occurrence of malignant neoplasms, and radiation cataracts. The pathogenesis of long-term effects of irradiation is largely associated with damage to tissues characterized by a low level of proliferative activity, which make up most of the organs of animals and humans. deep knowledge mechanisms of biological action ionizing radiation necessary, on the one hand, to develop methods radiation protection and pathogenetic treatment of radiation injuries, and, on the other hand, to find ways of directed enhancement of radiation exposure in radiation genetic work and other aspects of radiation biotechnology or in radiation therapy of malignant neoplasms using radiomodifying agents. In addition, understanding the mechanisms of biological action ionizing radiation is necessary for a doctor in case of urgent adoption of adequate measures to ensure the radiation safety of personnel and the public in case of accidents at nuclear power plants and other enterprises of the nuclear industry.
Bibliography: Gozenbuk V.L. and others. Dose load on a person in the fields of gamma-neutron radiation, M., 1978; Ivanov V.I. Course of dosimetry, M., 1988; Keirim-Markus I.B. Equidosimetry, M., 1980; Komar V.E. and Hanson K.P. Information macromolecules in radiation damage to cells, M., 1980; Moiseev A.A. and Ivanov V.I. Reference book on dosimetry and radiation hygiene, M., 1984; Yarmonenko S.P. Radiobiology of man and animals, M., 1988.
IONIZING RADIATIONS, streams of photons or particles, interaction. to-rykh with the environment leads to its ionization or. There are photon (electromagnetic) and corpuscular ionizing radiation. Photon ionizing radiation includes vacuum UV and characteristic X-ray radiation, as well as radiation arising from radioactive decay and other nuclear regions (ch. arr. g -radiation) and when braking charged particles in electric. or magn. field - bremsstrahlung X-rays, . Fluxes are referred to as corpuscular ionizing radiation a-and b -particles, accelerated and, fragments of heavy nuclei, etc. Charged particles ionize or media directly upon collision with them (primary ionization). If knocked out at the same time have sufficient kinetic. energy, they can also ionize or collide with environments (secondary ionization); such are called d -electrons. Photon radiation can ionize the medium both directly (direct ionization) and through those generated in the medium (indirect ionization); the contribution of each of these ionization pathways is determined by the photon energy and the atomic composition of the medium. The flows ionize the medium only indirectly, preim. recoil nuclei. Spatio-temporal distribution of charged particles or quanta that make up ionizing radiation, called. his field. Main characteristics of ionizing radiation: flux of ionizing radiation Ф n = dN/dt, where dN is the number of particles falling on a given surface in a time interval dt; flux density j n = dФ n /dS, where dФ n is the flow per cross-sectional area dS of the absorbing volume; energy flux Ф = dE/dt, where dE is the total radiation energy (excluding rest mass energy); the energy spectrum of ionizing radiation is the distribution of its constituent particles and photons by energy. The amount of energy transferred by ionizing radiation to a unit mass of the medium, called. absorbed radiation (see). All types of ionizing radiation are characterized by the so-called. (LEP) - the energy transferred to the medium by an ionizing particle in a given neighborhood of its trajectory per unit length. The LET can take values from 0.2 (high-energy photons and ) to 10 4 eV/nm (fragments of heavy nuclei).Interaction of radiation with the medium. During the passage of ionizing radiation in a medium, elastic scattering of the particles that make up the radiation and inelastic processes are possible. For elastic scattering kinetic energy relates. particle motion remains constant, but the direction of their motion changes, i.e. the flow of ionizing radiation is scattered; in inelastic kinetic processes. the energy of ionizing radiation is spent on ionization and excitation of the particles of the medium. The flow is characterized by elastic scattering on the nuclei of the medium and inelastic processes - ionization and excitation, and at interaction. with their electron shells (ionization losses) and the generation of bremsstrahlung at the interaction. c (radiation losses). If the energy does not exceed 10 MeV, ionization prevails in all media. losses. For a stream of accelerated ionization. losses dominate at all energies. The energy transmitted by a charged particle to a given substance per unit length of its path, called. stopping power in-va s m = dE / dl (dE is the energy lost by the particle during the passage of the elementary path dl). The value of s m decreases with an increase in the energy of charged particles and increases with an increase in at. the number of the element from which the in-in environment consists. The depth of penetration of charged particles into the water is characterized by the range R; c for He 2+ with an energy of 5.3 MeV R is 39 μm, for with an energy of 5 MeV -2.5 cm. For photon ionizing radiation, elastic scattering (classical scattering) and inelastic processes take place, the main of which are the photoelectric effect, the Compton effect and the formation of -. In the photoelectric effect, a photon is absorbed by the medium with emission, and the energy of the photon minus the binding energy in is transferred to the released one. The probability of the photoelectric effect from the K-shell is proportional to Z 5 (Z is the element's atom number) and rapidly decreases with increasing photon energy (curve 1 in Fig. 1). In the case of the Compton effect, a photon is scattered on one of the atomic ones; in this case, the photon energy decreases, the direction of its motion changes, and the medium is ionized. The probability of Compton scattering is proportional to Z and depends on the photon energy (curves 2 and 3 in Fig. 1). At a photon energy above 1.022 MeV, the formation of - becomes possible near the nucleus. The probability of this process is proportional to Z 2 and increases with increasing photon energy (curve 4 in Fig. 1). At photon energies up to 0.1 MeV, the classical one prevails. scattering and photoelectric effect, at energies from 0.1 to 10 MeV - the Compton effect, at energies above 20 MeV - formation. The attenuation of photon-ionizing radiation by a layer of matter occurs exponentially. law and is characterized by a linear coefficient. weakening m , which shows at what layer thickness in-va the intensity of the incident beam is attenuated by a factor of e. Usually, the attenuation of the radiation flux is measured and the mass coefficient is introduced. weakening m/r(r - density in-va): F n \u003d F 0 n e-(m/r) . r x , where x is the thickness of the layer in-va, Ф 0 n and Ф n are the incident and past flows, respectively. When a stream of photons passes through a medium, some of them are scattered, some are absorbed, therefore, mass coefficients are distinguished. weakening and absorption; second coefficient. numerically less than the first. Each type of interaction radiation with the medium is characterized by its mass coefficients, depending on the energy of photons and at. the number of the element from which the in-in environment consists. Neutron radiation interaction. only from Wednesday. By energy (in comparison with the average energy of thermal motion kT, where k - , T - abs. t-ra) are divided into cold (E< kT), тепловые (Е ~ kT), медленные (kT < E < 10 3 эВ), промежуточные (10 3
Rice. 1. Dependence of the mass attenuation coefficient
The depth of penetration of photon and neutron ionizing radiation into the medium is characterized by a layer of half attenuation
D 1/2 , which reduces the radiation flux by half. When D 1/2 = 9 cm for directional flow g - 60 Co radiation with an energy of 1.25 MeV and D 1/2 =8 cm for a directed flow with an average energy of 6 MeV. . interaction any ionizing radiation with particles of the medium lasts no more than 10 - 15 s. During this time, it is possible to rebuild the electronic subsystem of the environment (the nuclear subsystem remains unchanged). Interaction products appear in the medium: singly charged mainly and, decomp. energies, doubly charged, singlet and triplet, so-called. superexcited states (), having energy above the first I 1 particles of the medium. In the gas phase, the number exceeds the number formed, in the condenser. phase is the opposite. Ionization and excitation of particles of the medium can occur with any electronic energy. level, but the more probable the process, the lower the binding energy in and the medium. Interaction efficiency. ionizing radiation with the medium is characterized by an average energy W - the energy spent on the formation of one, and W exceeds I 1 by 1.5-2.5 times. Main a fraction of the energy of ionizing radiation is transferred by secondary d -electrons. Instantaneous distribution of primary and secondary energies in the medium - the so-called. radiation degradation spectrum - allows you to calculate all the processes of interaction. according to their sections in the system and find the composition and probability of formation decomp. ionized and . In the case of interaction ionizing radiation with (e.g., solution) the distribution of radiation energy between the components occurs in proportion to the electron fraction e of these components - the ratio of the number belonging to this component to the total number of all systems in a unit of mass (or volume). The energy of ionizing radiation transferred to-woo is distributed unevenly along the trajectory of ionizing particles, therefore spaces. distribution of products of interaction. also inhomogeneous. The degree of inhomogeneity is the higher, the greater the LET of radiation. This leads to unequal final effects in the interaction. with an environment of ionizing radiation with different LET (see Radiation-chemical). Sources of ionizing radiation differ in type and energy. radiation spectrum, design, location geometry irradiating elements, the power absorbed and its distribution in the irradiated object. Highlight the trace. groups: isotope sources, nuclear reactors, particle accelerators, X-ray installations. Among the isotopic sources, Naib. gamma-ray installations with long-lived 60 Co and l37 Cs are common.
Rice. 2. Scheme of a gamma-isotope source for irradiation: a - top view, b - side view; 1 - chamber for irradiation; 2 - room for loading 5; 3 - radiation source in working position; 4 - it is in the storage position; 6 - transport line for; 7 - control panel; 8 - concrete protection; 9 - teeth of the protective labyrinth; 10 - system for lifting sources from storage 11; 12 - console; 13 - dosimetric system. control.
On fig. Figure 2 shows a diagram of a gamma-ray setup for irradiating large objects. Radiating elements are located in the working chamber 1, which can be in working position 3 or in storage 4 (in this position, room 1 is accessible to people). Objects for irradiation are immersed in 5 and transport line 6 is delivered remotely to the irradiator 3. All rooms are under dosimetric. control 13. Ionizing radiation from nuclear reactors consists of
g -radiation, fast and thermal, fragments. Particle accelerators - devices that accelerate or in electric. field (the magnetic field can be used to control the flow of charged particles). There are two basic structural types of accelerators: linear, in which the charged particles move in a straight line, and cyclic, in which the movement goes along a circular trajectory. By type of accelerating electric field accelerators are divided into high-voltage, in which the direction of the electric. fields during acceleration does not change, and resonant, in which continuous acceleration is achieved due to the fact that the charged particle is in the accelerating phase of the alternating high-frequency electric. fields. In cyclical accelerators (cyclotron, synchrotron, synchrophasotron, etc.), the required energy is achieved by repeatedly passing the accelerated particle around the circumference of the apparatus, in linear (linear induction accelerator, linear resonant accelerator, etc.) - due to the application of high-frequency electric. field to a linear periodic. system. Main accelerator elements - a high-voltage generator, a source of charged particles (ion source) and a system in which acceleration is performed. In resonant accelerators, the process of energy accumulation by a particle occurs in a certain time, depending on the required energy and the type of particles being accelerated, therefore they operate in a pulsed mode. Certain types of high voltage accelerators (e.g. cascade accelerator) can be used in the regime of a constant flow of accelerated particles. Most types of accelerators are used for acceleration asionizing 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 exposed to it. Ionizing radiation is otherwise called radiation.
Radiation is a stream of particles (alpha particles, beta particles, neutrons) or electromagnetic energy of very high frequencies (gamma or x-rays).
Pollution of the production environment with substances that are sources of ionizing radiation is called radioactive contamination.
Nuclear pollution 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 activity.
Substances are made up of tiny particles of chemical elements - atoms. The atom is divisible and has a complex structure. At the center of an atom of a chemical element is a material particle called atomic nucleus around which the electrons revolve. Most of the atoms of chemical elements have great stability, i.e., stability. However, in a number of elements known in nature, the nuclei spontaneously decay. Such elements are called radionuclides. 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 certain chemical elements (radionuclides) is called radioactivity.
Radioactive radiation can be of various types: streams of particles with high energy, electromagnetic wave with a frequency of more than 1.5.10 17 Hz.
The emitted particles come in many forms, but the most commonly emitted are alpha particles (α-radiation) and beta particles (β-radiation). The alpha particle is heavy and has high energy; it is the nucleus of the helium atom. A beta particle is about 7336 times lighter than an alpha particle, but can also have high 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, turn into other radionuclides and chemical elements. Radionuclides decay with different speed. The decay rate of radionuclides is called activity. The unit of measure of activity is the number of decays per unit of time. One disintegration per second is called a 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 of measure of activity is named. The number of decays per second occurring in 1 g of radium-226 (activity) is 1 Ku.
The time it takes for half of a radionuclide to decay is called half-life(T 1/2). Each radionuclide has its own half-life. The range of T 1/2 for various radionuclides is very wide. It changes from seconds to billions of years. For example, the best known natural radionuclide, uranium-238, has a half-life of about 4.5 billion years.
During decay, the amount of the radionuclide decreases and its activity decreases. The pattern by which activity decreases obeys the law of radioactive decay:
where BUT 0 - initial activity, BUT- 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 vacuum devices, displays, etc.
Ionizing radiations are 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. Having 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 pairs of ions per 1 cm of the path in air.
Beta radiation - the flow of electrons or positrons resulting from radioactive decay.
The maximum range in the air of beta particles 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 power is higher than that of alpha particles.
Neutrons, the flux of which 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, ordinary ionization of a substance is possible.
The penetrating power of neutrons largely depends on their energy and the composition of the matter 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 a 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 is photon radiation with a continuous spectrum emitted when the kinetic energy of charged particles changes; characteristic radiation is a photon radiation with a discrete spectrum, emitted when the energy state of atoms changes.
Like gamma radiation, X-rays have a low ionizing power 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 radiation background consists of cosmic radiation and radiation of naturally distributed radioactive substances.
In addition to natural exposure, a person is exposed to exposure from other sources, for example: in the production of x-rays 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 minor short-lived 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. Lethal outcome in 100% of cases occurs at doses of 550-700 rem. Currently, there are a number of anti-radiation drugs. weakening the effect of radiation.
Chronic radiation sickness can develop with continuous or repeated exposure to doses significantly lower than those that cause an acute form. Most characteristic features 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, decreased immunity.
The degree depends on whether the exposure is external or internal. Internal exposure is possible by 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 local doses of radiation. For example, iodine isotopes accumulating in the body can cause damage thyroid gland, rare earth elements - liver tumors, isotopes of cesium, rubidium - soft tissue tumors.
Artificial sources of radiation
In addition to radiation from natural sources radiation, which were and are always and everywhere, in the 20th century, additional sources of radiation associated with human activity 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 zone they can reach 1000 rem or more. During x-ray examinations, the dose depends on the time of the examination and the organ that is being diagnosed, and can vary widely - from a few rem when taking a picture of a tooth to tens of rem when examining the gastrointestinal tract and lungs. Fluorographic images give the minimum dose, and preventive annual fluorographic examinations should by no means be abandoned. The average dose people 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 diagnostics of technical objects, in instrumentation, etc. And finally, nuclear power. Nuclear power plants are used at nuclear power plants (NPPs), icebreakers, ships, and submarines. Currently, more than 400 nuclear reactors with a total electrical capacity of over 300 million kW are operating at nuclear power plants alone. For the production and processing of nuclear fuel, a whole complex of enterprises united in nuclear fuel cycle(NFC).
The NFC includes enterprises for uranium mining (uranium mines), its enrichment (concentration plants), 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 resulting radioactive waste of the nuclear fuel cycle, and, finally, points for the permanent disposal of radioactive waste (repositories). At all stages of the NFC, radioactive substances affect the operating personnel to a greater or lesser extent, at all stages, releases (normal or accidental) of radionuclides into the environment can occur and create an additional dose for the population, especially those living in the area of the NFC enterprises.
Where do radionuclides come from? normal operation NUCLEAR POWER STATION? Radiation inside nuclear reactor huge. Fuel fission fragments, various elementary particles can penetrate protective shells, microcracks and enter the coolant and air. Whole line technological operations in the production of electricity at nuclear power plants can lead to water and air pollution. Therefore, nuclear power plants are equipped with a water and gas cleaning system. Emissions to the atmosphere are carried out through a tall chimney.
During normal operation of nuclear power plants, emissions to the environment are small and have little impact on the population living in the vicinity.
The greatest danger from the point of view of radiation safety is posed by plants for the processing of spent nuclear fuel, which has a very high activity. These enterprises generate a large amount of liquid waste with high radioactivity, there is a danger of developing a spontaneous chain reaction (nuclear hazard).
The problem of dealing with radioactive waste, which is a very significant source of radioactive contamination of the biosphere, is very difficult.
However, complex and costly from radiation at NFC enterprises make it possible to ensure the protection of humans and the environment to very small values, significantly less than the existing technogenic background. Another situation occurs when there is a deviation from the normal mode of operation, and especially during accidents. Thus, the accident that occurred in 1986 (which can be classified as a disaster on a global scale is the most major accident at the enterprises of the nuclear fuel cycle throughout the history of the development of nuclear energy) 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 resulted in the exposure of a large number of people, a large number deaths, pollution of very large areas, the need for mass relocation of people.
The accident at the Chernobyl nuclear power plant clearly showed that the nuclear method of generating energy is possible only if large-scale accidents at nuclear fuel cycle enterprises are ruled out in principle.
51. Ionizing radiation. Types of ionizing radiation, main characteristics.
AI are divided into 2 types:
Corpuscular radiation
- 𝛼-radiation is a stream of helium nuclei emitted by a substance during radioactive decay or during nuclear reactions;
- 𝛽-radiation - a stream of electrons or positrons arising from radioactive decay;
Neutron radiation (With elastic interactions, the usual ionization of matter occurs. With inelastic interactions, secondary radiation occurs, which can consist of both charged particles and quanta).
2. Electromagnetic radiation
- 𝛾-radiation is electromagnetic (photon) radiation emitted during nuclear transformations or interaction of particles;
X-ray radiation - occurs in the environment surrounding the radiation source, in x-ray tubes.
AI characteristics: energy (MeV); speed (km/s); mileage (in air, in living tissue); ionizing capacity (pair of ions per 1 cm path in air).
The lowest ionizing ability of α-radiation.
Charged particles lead to direct, strong ionization.
Activity (A) of a radioactive substance is the number of spontaneous nuclear transformations (dN) in this substance in a short period of time (dt):
1 Bq (becquerel) is equal to one nuclear transformation per second.
52. Ionizing radiation. Doses of ionizing radiation and units of their measurement.
Ionizing radiation (IR) is radiation, the interaction of which with the medium leads to the formation of charges of opposite signs. Ionizing radiation occurs during radioactive decay, nuclear transformations, as well as during the interaction of charged particles, neutrons, photon (electromagnetic) radiation with matter.
Radiation dose is the value used to assess exposure to ionizing radiation.
Exposure dose(characterizes the radiation source by the ionization effect):
Exposure dose at the workplace when working with radioactive substances:
where A is the activity of the source [mCi], K is the gamma constant of the isotope [Rcm2/(hmCi)], t is the exposure time, r is the distance from the source to the workplace [cm].
Dose rate(irradiation intensity) - the increment of the corresponding dose under the influence of this radiation per unit. time.
Exposure dose rate [rh -1 ].
Absorbed dose shows how much AI energy is absorbed by the unit. masses of the irradiated in-va:
D absorption = D exp. K 1
where K 1 - coefficient taking into account the type of irradiated substance
Absorption dose, Gray, [J/kg]=1Gy
Dose equivalent characterized by chronic exposure to radiation of arbitrary composition
H = D Q [Sv] 1 Sv = 100 rem.
Q is a dimensionless weighting factor for a given type of radiation. For X-ray and -radiation Q=1, for alpha-, beta-particles and neutrons Q=20.
Effective equivalent dose character sensitivity decomp. organs and tissues to radiation.
Irradiation of inanimate objects - Absorb. dose
Irradiation of living objects - Equiv. dose
53. The effect of ionizing radiation(AI) on the body. External and internal exposure.
The biological effect of AI is based on the ionization of living tissue, which leads to the breaking of molecular bonds and a change in the chemical structure of various compounds, which leads to a change in the DNA of cells and their subsequent death.
Violation of the vital processes of the body is expressed in such disorders as
Inhibition of the functions of the hematopoietic organs,
Violation of normal blood clotting and increased fragility of blood vessels,
Disorder of the gastrointestinal tract,
Decreased resistance to infections
Depletion of the body.
External exposure occurs when the source of radiation is outside the human body and there are no ways for them to get inside.
Internal exposure origin when the source of AI is inside a person; while the internal Irradiation is also dangerous due to the proximity of the IR source to organs and tissues.
threshold effects (Н > 0.1 Sv/year) depend on the IR dose, occur with lifetime exposure doses
Radiation sickness is a disease that is characterized by symptoms that occur when exposed to AI, such as a decrease in hematopoietic ability, gastrointestinal upset, and a decrease in immunity.
The degree of radiation sickness depends on the radiation dose. The most severe is the 4th degree, which occurs when exposed to AI with a dose of more than 10 Gray. Chronic radiation injuries are usually caused by internal exposure.
Non-threshold (stochastic) effects appear at doses of H<0,1 Зв/год, вероятность возникновения которых не зависит от дозы излучения.
Stochastic effects include:
Somatic changes
Immune changes
genetic changes
The principle of rationing – i.e. non-exceeding of permissible limits individual. Radiation doses from all AI sources.
Justification principle – i.e. prohibition of all types of activity on the use of AI sources, in which the benefit received for a person and society does not exceed the risk of possible harm caused in addition to natural radiation. fact.
Optimization principle - maintenance at the lowest possible and achievable level, taking into account the economic. and social individual factors. exposure doses and the number of exposed persons when using an AI source.
SanPiN 2.6.1.2523-09 "Radiation safety standards".
In accordance with this document, 3 gr. persons:
gr.A - these are faces, for sure. working with man-made sources of AI
gr .B - these are persons, conditions for the work of the cat nah-Xia in the immediate. breeze from the AI source, but deyat. these persons immediately. is not connected with the source.
gr .AT is the rest of the population, incl. persons gr. A and B outside of their production activities.
The main dose limit is set. by effective dose:
For persons gr.A: 20mSv per year on Wed. for the next 5 years, but not more than 50 mSv in year.
For persons group B: 1mSv per year on Wed. for the next 5 years, but not more than 5 mSv in year.
For persons group B: should not exceed ¼ of the values for personnel group A.
In case of an emergency caused by a radiation accident, there is a so-called. peak increased exposure, cat. is allowed only in those cases when it is not possible to take measures excluding harm to the body.
The use of such doses can be justified only by saving lives and preventing accidents, additional only for men over 30 years of age with a voluntary written agreement.
AI protection m/s:
Qty protection
time protection
Distance protection
Zoning
Remote control
Shielding
For protection againstγ -radiation: metallic screens made with a large atomic weight (W, Fe), as well as from concrete, cast iron.
For protection against β-radiation: materials with a low atomic mass (aluminum, plexiglass) are used.
For protection against α-radiation: use metals containing H2 (water, paraffin, etc.)
Screen thickness К=Ро/Рdop, Ро – power. dose, measured per rad. place; Rdop - maximum allowable dose.
Zoning - division of the territory into 3 zones: 1) shelter; 2) objects and premises in which people can find; 3) zone post. stay of people.
Dosimetric control based on isp-ii trace. methods: 1. Ionization 2. Phonographic 3. Chemical 4. Calorimetric 5. Scintillation.
Basic appliances , used for dosimetric. control:
X-ray meter (for measuring powerful exp. doses)
Radiometer (to measure AI flux density)
Individual. dosimeters (for measuring exposure or absorbed dose).