The influence of ionizing radiation on the human body. Ionizing radiation

Ionizing radiation is radiation whose interaction with a substance leads to the formation of ions of different signs in this substance. Ionizing radiation consists of charged and uncharged particles, which also include photons. The energy of particles of ionizing radiation is measured in extra-systemic units - electron volts, eV. 1 eV = 1.6 10 -19 J.

There are corpuscular and photon ionizing radiation.

Corpuscular ionizing radiation- a flow of elementary particles with a rest mass different from zero, formed during radioactive decay, nuclear transformations, or generated in accelerators. It includes: α- and β-particles, neutrons (n), protons (p), etc.

α-radiation is a stream of particles that are the nuclei of a helium atom and have two units of charge. The energy of α-particles emitted by various radionuclides lies in the range of 2-8 MeV. In this case, all nuclei of a given radionuclide emit α-particles having the same energy.

β-radiation is a stream of electrons or positrons. During the decay of the nuclei of a β-active radionuclide, in contrast to α-decay, different nuclei of a given radionuclide emit β-particles of different energies, therefore the energy spectrum of β-particles is continuous. The average energy of the β spectrum is approximately 0.3 E tah. The maximum energy of β-particles for currently known radionuclides can reach 3.0-3.5 MeV.

Neutrons (neutron radiation) are neutral elementary particles. Since neutrons have no electrical charge, when passing through matter they interact only with the nuclei of atoms. As a result of these processes, either charged particles (recoil nuclei, protons, neutrons) or g-radiation are formed, causing ionization. According to the nature of interaction with the environment, depending on the energy level of neutrons, they are conventionally divided into 4 groups:

1) thermal neutrons 0.0-0.5 keV;

2) intermediate neutrons 0.5-200 keV;

3) fast neutrons 200 KeV - 20 MeV;

4) relativistic neutrons above 20 MeV.

Photon radiation- a stream of electromagnetic oscillations that propagate in a vacuum at a constant speed of 300,000 km/s. This includes g-radiation, characteristic, bremsstrahlung and x-ray
radiation.

Possessing the same nature, these types of electromagnetic radiation differ in the conditions of formation, as well as properties: wavelength and energy.

Thus, g-radiation is emitted during nuclear transformations or during the annihilation of particles.

Characteristic radiation is photon radiation with a discrete spectrum, emitted when the energy state of the atom changes, caused by the restructuring of the internal electron shells.

Bremsstrahlung radiation is associated with a change in the kinetic energy of charged particles, has a continuous spectrum and occurs in the environment surrounding the source of β-radiation, in X-ray tubes, in electron accelerators, etc.

X-ray radiation is a combination of bremsstrahlung and characteristic radiation, the photon energy range of which is 1 keV - 1 MeV.

Radiations are characterized by their ionizing and penetrating ability.

Ionizing power radiation is determined by specific ionization, i.e., the number of ion pairs created by a particle per unit volume of mass of the medium or per unit path length. Different types of radiation have different ionizing properties.

Penetration ability radiation is determined by the range. The distance is the distance traveled by a particle in a substance until it comes to a complete stop due to one or another type of interaction.

α-particles have the greatest ionizing ability and the least penetrating ability. Their specific ionization varies from 25 to 60 thousand pairs of ions per 1 cm of path in the air. The travel distance of these particles in the air is several centimeters, and in soft biological tissue - several tens of microns.

β-radiation has a significantly lower ionizing ability and greater penetrating ability. The average value of specific ionization in air is about 100 pairs of ions per 1 cm of path, and the maximum range reaches several meters at high energies.

Photon radiation has the lowest ionizing ability and the highest penetrating ability. In all processes of interaction of electromagnetic radiation with the environment, part of the energy is converted into the kinetic energy of secondary electrons, which, passing through the substance, produce ionization. The passage of photon radiation through matter cannot be characterized at all by the concept of range. The attenuation of the flow of electromagnetic radiation in a substance obeys an exponential law and is characterized by an attenuation coefficient p, which depends on the radiation energy and the properties of the substance. But whatever the thickness of the layer of matter, it is impossible to completely absorb the flux of photon radiation, but you can only weaken its intensity by any number of times.

This is a significant difference in the nature of the attenuation of photon radiation from the attenuation of charged particles, for which there is a minimum thickness of the layer of absorbent substance (range), where the flow of charged particles is completely absorbed.

Biological effects of ionizing radiation. Under the influence of ionizing radiation on the human body, complex physical and biological processes can occur in tissues. As a result of ionization of living tissue, molecular bonds are broken and the chemical structure of various compounds changes, which in turn leads to cell death.

An even more significant role in the formation of biological consequences is played by the products of radiolysis of water, which makes up 60-70% of the mass of biological tissue. Under the influence of ionizing radiation on water, free radicals H and OH are formed, and in the presence of oxygen, also free radicals of hydroperoxide (HO 2) and hydrogen peroxide (H 2 O 2), which are strong oxidizing agents. Radiolysis products enter into chemical reactions with tissue molecules, forming compounds that are not characteristic of a healthy body. This leads to disruption of individual functions or systems, as well as the functioning of the body as a whole.

The intensity of chemical reactions induced by free radicals increases, and they involve many hundreds and thousands of molecules not affected by radiation. This is the specificity of the action of ionizing radiation on biological objects, that is, the effect produced by radiation is determined not so much by the amount of absorbed energy in the irradiated object, but by the form in which this energy is transmitted. No other type of energy (thermal, electrical, etc.), absorbed by a biological object in the same amount, leads to such changes as those caused by ionizing radiation.

Ionizing radiation when exposed to the human body can cause two types of effects that are classified as diseases in clinical medicine: deterministic threshold effects (radiation sickness, radiation burn, radiation cataract, radiation infertility, abnormalities in fetal development, etc.) and stochastic (probabilistic) non-threshold effects (malignant tumors, leukemia, hereditary diseases).

Disturbances in biological processes can be either reversible, when the normal functioning of the cells of the irradiated tissue is completely restored, or irreversible, leading to damage to individual organs or the entire organism and the occurrence of radiation sickness.

There are two forms of radiation sickness - acute and chronic.

Acute form occurs as a result of exposure to large doses in a short period of time. At doses of the order of thousands of rads, damage to the body can be instantaneous (“death under the ray”). Acute radiation sickness can also occur when large quantities of radionuclides enter the body.

Acute lesions develop with a single uniform gamma irradiation of the whole body and an absorbed dose above 0.5 Gy. At a dose of 0.25...0.5 Gy, temporary changes in the blood may be observed, which quickly normalize. In the dose range of 0.5...1.5 Gy, a feeling of fatigue occurs, less than 10% of those exposed may experience vomiting and moderate changes in the blood. At a dose of 1.5...2.0 Gy, a mild form of acute radiation sickness is observed, which is manifested by prolonged lymphopenia (decrease in the number of lymphocytes - immunocompetent cells), in 30...50% of cases - vomiting on the first day after irradiation. No deaths are recorded.

Moderate radiation sickness occurs at a dose of 2.5...4.0 Gy. Almost all irradiated people experience nausea and vomiting on the first day, the content of leukocytes in the blood sharply decreases, subcutaneous hemorrhages appear, in 20% of cases death is possible, death occurs 2-6 weeks after irradiation. At a dose of 4.0...6.0 Gy, a severe form of radiation sickness develops, leading in 50% of cases to death within the first month. At doses exceeding 6.0 Gy, an extremely severe form of radiation sickness develops, which in almost 100% of cases ends in death due to hemorrhage or infectious diseases. The data given refers to cases where there is no treatment. Currently, there are a number of anti-radiation agents that, with complex treatment, can eliminate death at doses of about 10 Gy.

Chronic radiation sickness can develop with continuous or repeated exposure to doses significantly lower than those that cause the acute form. The most characteristic signs of chronic radiation sickness are changes in the blood, a number of symptoms from the nervous system, local skin lesions, lesions of the lens, pneumosclerosis (with inhalation of plutonium-239), and a decrease in the body’s immunoreactivity.

The degree of exposure to radiation depends on whether the exposure is external or internal (when a radioactive isotope enters the body). Internal exposure is possible through inhalation, ingestion of radioisotopes and their penetration into the body through the skin. Some substances are absorbed and accumulated in specific organs, resulting in high local doses of radiation. Calcium, radium, strontium and others accumulate in bones, iodine isotopes cause damage to the thyroid gland, rare earth elements - mainly liver tumors. Cesium and rubidium isotopes are evenly distributed, causing inhibition of hematopoiesis, atrophy of the testes, and soft tissue tumors. In internal irradiation, the most dangerous are the alpha-emitting isotopes of polonium and plutonium.

The ability to cause long-term consequences - leukemia, malignant neoplasms, early aging - is one of the insidious properties of ionizing radiation.

To solve radiation safety issues, the effects observed at “low doses” - on the order of several centisieverts per hour and below, which actually occur in the practical use of atomic energy - are primarily of interest.

It is very important here that, according to modern concepts, the yield of adverse effects in the range of “low doses” encountered under normal conditions depends little on the dose rate. This means that the effect is determined primarily by the total accumulated dose, regardless of whether it is received in 1 day, 1 s or 50 years. Thus, when assessing the effects of chronic exposure, it should be borne in mind that these effects accumulate in the body over a long period of time.

Dosimetric quantities and units of their measurement. The effect of ionizing radiation on matter is manifested in the ionization and excitation of atoms and molecules that make up the substance. The absorbed dose is a quantitative measure of this effect. D p- the average energy transferred by radiation to a unit mass of matter. The unit of absorbed dose is the gray (Gy). 1 Gy = 1 J/kg. In practice, an off-system unit is also used - 1 rad = 100 erg/g = 1 10 -2 J/kg = 0.01 Gy.

The absorbed dose of radiation depends on the properties of the radiation and the absorbing medium.

For charged particles (α, β, protons) of low energies, fast neutrons and some other radiation, when the main processes of their interaction with matter are direct ionization and excitation, the absorbed dose serves as an unambiguous characteristic of ionizing radiation based on its effect on the environment. This is due to the fact that adequate direct relationships can be established between the parameters characterizing these types of radiation (flux, flux density, etc.) and the parameter characterizing the ionization ability of radiation in the medium - the absorbed dose.

For X-ray and g-radiation such dependences are not observed, since these types of radiation are indirectly ionizing. Consequently, the absorbed dose cannot serve as a characteristic of these radiations in terms of their effect on the environment.

Until recently, the so-called exposure dose was used as a characteristic of X-ray and g-radiation based on the ionization effect. The exposure dose expresses the energy of photon radiation converted into the kinetic energy of secondary electrons producing ionization per unit mass of atmospheric air.

The unit of exposure dose of X-ray and g-radiation is taken to be a coulomb per kilogram (C/kg). This is a dose of X-ray or g-radiation, when exposed to 1 kg of dry atmospheric air under normal conditions, ions are formed that carry 1 C of electricity of each sign.

In practice, the non-systemic unit of exposure dose, the x-ray, is still widely used. 1 roentgen (P) - exposure dose of X-ray and g-radiation, at which ions are formed in 0.001293 g (1 cm 3 of air under normal conditions), carrying a charge of one electrostatic unit of the amount of electricity of each sign or 1 P = 2.58 10 -4 C/kg. With an exposure dose of 1 R, 2.08 10 9 pairs of ions will be formed in 0.001293 g of atmospheric air.

Studies of the biological effects caused by various ionizing radiations have shown that tissue damage is associated not only with the amount of absorbed energy, but also with its spatial distribution, characterized by linear ionization density. The higher the linear ionization density, or, in other words, the linear energy transfer of particles in the medium per unit path length (LET), the greater the degree of biological damage. To take this effect into account, the concept of equivalent dose was introduced.

Dose equivalent to H T, R - absorbed dose in an organ or tissue D T , R , multiplied by the appropriate weighting factor for a given radiation W R:

H t , r=W R D T , R

The unit of equivalent dose is J kg -1, which has a special name sievert (Sv).

Values W R for photons, electrons and muons of any energy is 1, for α-particles, fission fragments, heavy nuclei - 20. Weighting factors for individual types of radiation when calculating the equivalent dose:

· Photons of any energy…………………………………………………….1

· Electrons and muons (less than 10 keV)……………………………………………………….1

· Neutrons with energy less than 10 keV………………………………………………………...5

from 10 keV to 100 keV……....……………………………………………………………10

from 100 keV to 2 MeV………………………………………………………..20

from 2 MeV to 20 MeV………………………………………………………..10

more than 20 MeV…………………………………………………………………………………5

Protons, other than recoil protons,

energy more than 2 MeV………………………………….………………5

Alpha particles

fission fragments, heavy nuclei………………………………………….20

Effective dose- a value used as a measure of the risk of long-term consequences of irradiation of the entire human body and its individual organs, taking into account their radiosensitivity. It represents the sum of the products of the equivalent dose in the organ N τT by the appropriate weighting factor for a given organ or tissue W T:

Where N τT - tissue equivalent dose T during τ .

The unit of effective dose is J × kg -1, called the sievert (Sv).

Values W T for individual types of tissue and organs are given below:

Type of tissue, organ W 1

Gonads........................................................ ........................................................ .............0.2

Bone marrow, (red), lungs, stomach………………………………0.12

Liver, mammary gland, thyroid gland. …………………………...0.05

Leather………………………………………………………………………………………0.01

Absorbed, exposure and equivalent doses per unit of time are called the power of the corresponding doses.

Spontaneous (spontaneous) decay of radioactive nuclei follows the law:

N=N0 exp(-λt),

Where N 0- the number of nuclei in a given volume of matter at time t = 0; N- number of nuclei in the same volume at time t ; λ is the decay constant.

The constant λ has the meaning of the probability of nuclear decay in 1 s; it is equal to the fraction of nuclei that decay in 1 s. The decay constant does not depend on the total number of nuclei and has a very specific value for each radioactive nuclide.

The above equation shows that over time, the number of nuclei of a radioactive substance decreases exponentially.

Due to the fact that the half-life of a significant number of radioactive isotopes is measured in hours and days (the so-called short-lived isotopes), it is necessary to know it to assess the radiation hazard over time in the event of an emergency release of a radioactive substance into the environment, choosing a decontamination method, as well as during processing radioactive waste and its subsequent disposal.

The types of doses described relate to an individual person, that is, they are individual.

By summing up the individual effective equivalent doses received by a group of people, we arrive at a collective effective equivalent dose, which is measured in man-sieverts (man-Sv).

One more definition needs to be introduced.

Many radionuclides decay very slowly and will remain in the distant future.

The collective effective equivalent dose that generations of people will receive from any radioactive source over the entire period of its existence is called expected (total) collective effective equivalent dose.

Drug activity - it is a measure of the amount of radioactive material.

Activity is determined by the number of decaying atoms per unit time, that is, the rate of decay of radionuclide nuclei.

The unit of activity is one nuclear transformation per second. In the SI system of units it is called becquerel (Bq).

The extra-systemic unit of activity is taken to be the curie (Ci) - the activity of that number of radionuclide in which 3.7 × 10 10 decay events occur per second. In practice, derivatives of Ci are widely used: millicurie - 1 mCi = 1 ×10 -3 Ci; microcurie - 1 µCi = 1 ×10 -6 Ci.

Measurement of ionizing radiation. It must be remembered that there are no universal methods and instruments applicable to all conditions. Each method and device has its own area of application. Failure to take these comments into account can lead to serious mistakes.

Radiometers, dosimeters and spectrometers are used in radiation safety.

Radiometers- these are instruments designed to determine the amount of radioactive substances (radionuclides) or radiation flux. For example, gas-discharge counters (Geiger-Muller).

Dosimeters- these are devices for measuring exposure or absorbed dose rate.

Spectrometers serve for registration and analysis of the energy spectrum and identification of emitting radionuclides on this basis.

Rationing. Radiation safety issues are regulated by the Federal Law “On Radiation Safety of the Population”, radiation safety standards (NRB-99) and other rules and regulations. The Law “On Radiation Safety of the Population” states: “Radiation safety of the population is the state of protection of present and future generations of people from the harmful effects of ionizing radiation on their health” (Article 1).

“Citizens of the Russian Federation, foreign citizens and stateless persons living on the territory of the Russian Federation have the right to radiation safety. This right is ensured through the implementation of a set of measures to prevent radiation exposure on the human body from ionizing radiation above established norms, rules and regulations, and compliance by citizens and organizations carrying out activities using sources of ionizing radiation with radiation safety requirements” (Article 22).

Hygienic regulation of ionizing radiation is carried out by Radiation Safety Standards NRB-99 (Sanitary Rules SP 2.6.1.758-99). Basic radiation dose limits and permissible levels are established for the following categories

exposed persons:

· personnel - persons working with man-made sources (group A) or who, due to working conditions, are in the sphere of their influence (group B);

· the entire population, including personnel, outside the scope and conditions of their production activities.

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Introduction

Natural ionizing radiation is present everywhere. It comes from space in the form of cosmic rays. It is in the air in the form of radiation from radioactive radon and its secondary particles. Radioactive isotopes of natural origin penetrate into all living organisms with food and water and remain in them. Ionizing radiation cannot be avoided. A natural radioactive background has always existed on Earth, and life arose in the field of its radiation, and then - much, much later - man appeared. This natural (natural) radiation accompanies us throughout our lives.

The physical phenomenon of radioactivity was discovered in 1896, and today it is widely used in many fields. Despite radiophobia, nuclear power plants play an important role in the energy sector in many countries. X-rays are used in medicine to diagnose internal injuries and diseases. A number of radioactive substances are used in the form of labeled atoms to study the functioning of internal organs and study metabolic processes. Radiation therapy uses gamma radiation and other types of ionizing radiation to treat cancer. Radioactive substances are widely used in various monitoring devices, and ionizing radiation (primarily X-rays) is used for industrial flaw detection purposes. Exit signs on buildings and airplanes contain radioactive tritium to glow in the dark in the event of a sudden power outage. Many fire alarm devices in residential and public buildings contain radioactive americium.

Radioactive radiation of different types with different energy spectrums are characterized by different penetrating and ionizing abilities. These properties determine the nature of their impact on the living matter of biological objects.

It is believed that some of the hereditary changes and mutations in animals and plants are associated with background radiation.

In the event of a nuclear explosion, a center of nuclear damage appears on the ground - an area where the factors of mass destruction of people are light radiation, penetrating radiation and radioactive contamination of the area.

As a result of the damaging effects of light radiation, massive burns and eye damage can occur. Various types of shelters are suitable for protection, and in open areas - special clothing and glasses.

Penetrating radiation consists of gamma rays and a stream of neutrons emanating from the nuclear explosion zone. They can spread over thousands of meters, penetrate into various environments, causing ionization of atoms and molecules. Penetrating into the tissues of the body, gamma rays and neutrons disrupt biological processes and functions of organs and tissues, resulting in the development of radiation sickness. Radioactive contamination of the area is created due to the adsorption of radioactive atoms by soil particles (the so-called radioactive cloud, which moves in the direction of air movement). The main danger for people in contaminated areas is external beta-gamma radiation and the ingress of nuclear explosion products into the body and onto the skin.

Nuclear explosions, releases of radionuclides from nuclear power plants and the widespread use of sources of ionizing radiation in various industries, agriculture, medicine and scientific research have led to a global increase in exposure of the Earth's population. In addition to natural exposure, anthropogenic sources of external and internal exposure have been added.

During nuclear explosions, fission radionuclides, induced activity and the undivided part of the charge (uranium, plutonium) enter the environment. Induced activity occurs when neutrons are captured by the nuclei of atoms of elements located in the structure of the product, air, soil and water. According to the nature of the radiation, all radionuclides of fission and induced activity are classified as - or - emitters.

Fallouts are divided into local and global (tropospheric and stratospheric). Local fallout, which may include over 50% of the radioactive material produced in ground explosions, is large aerosol particles falling at a distance of about 100 km from the explosion site. Global fallout is caused by fine aerosol particles.

Radionuclides falling on the surface of the earth become a source of long-term radiation.

Human exposure to radioactive fallout includes external -, -irradiation due to radionuclides present in the ground air and fallen on the surface of the earth, contact as a result of contamination of the skin and clothing, and internal from radionuclides entering the body with inhaled air and contaminated food and water. The critical radionuclide in the initial period is radioactive iodine, and subsequently 137Cs and 90Sr.

1. History of the discovery of radioactive radiation

Radioactivity was discovered in 1896 by the French physicist A. Becquerel. He studied the connection between luminescence and the recently discovered x-rays.

Becquerel came up with an idea: isn’t all luminescence accompanied by X-rays? To test his guess, he took several compounds, including one of the uranium salts, which phosphorescent with yellow-green light. Having illuminated it with sunlight, he wrapped the salt in black paper and placed it in a dark closet on a photographic plate, also wrapped in black paper. After some time, developing the plate, Becquerel actually saw the image of a piece of salt. But luminescent radiation could not pass through black paper, and only X-rays could illuminate the plate under these conditions. Becquerel repeated the experiment several times with equal success. At the end of February 1896, at a meeting of the French Academy of Sciences, he made a report on the X-ray emission of phosphorescent substances.

After some time, in Becquerel’s laboratory, a plate was accidentally developed on which lay a uranium salt that had not been irradiated by sunlight. Naturally, it did not phosphorescent, but there was an imprint on the plate. Then Becquerel began testing various uranium compounds and minerals (including those that did not exhibit phosphorescence), as well as metallic uranium. The record was invariably overexposed. By placing a metal cross between the salt and the plate, Becquerel obtained faint outlines of the cross on the plate. Then it became clear that new rays had been discovered that passed through opaque objects, but were not x-rays.

Becquerel established that the intensity of radiation is determined only by the amount of uranium in the preparation and is completely independent of what compounds it is included in. Thus, this property was inherent not in compounds, but in the chemical element uranium.

Becquerel shares his discovery with the scientists with whom he collaborated. In 1898, Marie Curie and Pierre Curie discovered the radioactivity of thorium, and later they discovered the radioactive elements polonium and radium.

They found that all uranium compounds, and most importantly uranium itself, have the property of natural radioactivity. Becquerel returned to the phosphors that interested him. True, he made another major discovery related to radioactivity. Once, for a public lecture, Becquerel needed a radioactive substance, he took it from the Curies and put the test tube in his vest pocket. After giving a lecture, he returned the radioactive drug to the owners, and the next day he discovered redness of the skin in the shape of a test tube on his body under his vest pocket. Becquerel told Pierre Curie about this, and he experimented on himself: he wore a test tube of radium tied to his forearm for ten hours. A few days later he also developed redness, which then turned into a severe ulcer, from which he suffered for two months. This was the first time the biological effects of radioactivity were discovered.

But even after this, the Curies courageously did their job. Suffice it to say that Marie Curie died of radiation sickness (however, she lived to be 66 years old).

In 1955, Marie Curie's notebooks were examined. They still emit radiation, thanks to radioactive contamination introduced when they were filled. One of the sheets bears Pierre Curie's radioactive fingerprint.

The concept of radioactivity and types of radiation.

Radioactivity is the ability of some atomic nuclei to spontaneously transform into other nuclei with the emission of various types of radioactive radiation and elementary particles. Radioactivity is divided into natural (observed in unstable isotopes existing in nature) and artificial (observed in isotopes obtained through nuclear reactions).

Radioactive radiation is divided into three types:

Radiation - deflected by electric and magnetic fields, has high ionizing ability and low penetrating ability; represents a flow of helium nuclei; the charge of the -particle is +2e, and the mass coincides with the mass of the nucleus of the helium isotope 42He.

Radiation - deflected by electric and magnetic fields; its ionizing ability is much lower (by approximately two orders of magnitude), and its penetrating ability is much greater than that of -particles; is a stream of fast electrons.

Radiation - is not deflected by electric and magnetic fields, has a relatively weak ionizing ability and very high penetrating ability; is short-wave electromagnetic radiation with an extremely short wavelength< 10-10 м и вследствие этого - ярко выраженными корпускулярными свойствами, то есть является поток частиц - -квантов (фотонов).

Half-life T1/2 is the time during which the initial number of radioactive nuclei is halved on average.

Alpha radiation is a stream of positively charged particles formed by 2 protons and 2 neutrons. The particle is identical to the nucleus of the helium-4 atom (4He2+). Formed during alpha decay of nuclei. Alpha radiation was first discovered by E. Rutherford. Studying radioactive elements, in particular studying such radioactive elements as uranium, radium and actinium, E. Rutherford came to the conclusion that all radioactive elements emit alpha and beta rays. And, more importantly, the radioactivity of any radioactive element decreases after a certain specific period of time. The source of alpha radiation is radioactive elements. Unlike other types of ionizing radiation, alpha radiation is the most harmless. It is dangerous only when such a substance enters the body (inhalation, eating, drinking, rubbing, etc.), since the range of an alpha particle, for example with an energy of 5 MeV, in the air is 3.7 cm, and in biological tissue 0. 05 mm. Alpha radiation from a radionuclide that enters the body causes truly terrible destruction, because The quality factor for alpha radiation with energy less than 10 MeV is 20 mm. and energy losses occur in a very thin layer of biological tissue. It practically burns him. When alpha particles are absorbed by living organisms, mutagenic (factors that cause mutation), carcinogenic (substances or a physical agent (radiation) that can cause the development of malignant tumors) and other negative effects may occur. Penetrating ability of A.-i. small because held up by a sheet of paper.

Beta particle (beta particle), a charged particle emitted by beta decay. The stream of beta particles is called beta rays or beta radiation.

Negatively charged beta particles are electrons (b--), positively charged beta particles are positrons (b+).

The energies of beta particles are distributed continuously from zero to some maximum energy, depending on the decaying isotope; this maximum energy ranges from 2.5 keV (for rhenium-187) to tens of MeV (for short-lived nuclei far from the beta stability line).

Beta rays are deviated from the straight direction under the influence of electric and magnetic fields. The speed of particles in beta rays is close to the speed of light. Beta rays are capable of ionizing gases, causing chemical reactions, luminescence, and affecting photographic plates.

Significant doses of external beta radiation can cause radiation burns to the skin and lead to radiation sickness. Even more dangerous is internal radiation from beta-active radionuclides that enter the body. Beta radiation has significantly less penetrating power than gamma radiation (however, an order of magnitude greater than alpha radiation). A layer of any substance with a surface density of about 1 g/cm2.

For example, a few millimeters of aluminum or several meters of air almost completely absorbs beta particles with an energy of about 1 MeV.

Gamma radiation is a type of electromagnetic radiation with an extremely short wavelength --< 5Ч10-3 нм и вследствие этого ярко выраженными корпускулярными и слабо выраженными волновыми свойствами. Гамма-квантами являются фотоны высокой энергии. Обычно считается, что энергии квантов гамма-излучения превышают 105 эВ, хотя резкая граница между гамма- и рентгеновским излучением не определена. На шкале электромагнитных волн гамма-излучение граничит с рентгеновским излучением, занимая диапазон более высоких частот и энергий. В области 1-100 кэВ гамма-излучение и рентгеновское излучение различаются только по источнику: если квант излучается в ядерном переходе, то его принято относить к гамма-излучению, если при взаимодействиях электронов или при переходах в атомной электронной оболочке -- то к рентгеновскому излучению. Очевидно, физически кванты электромагнитного излучения с одинаковой энергией не отличаются, поэтому такое разделение условно.

Gamma radiation is emitted during transitions between excited states of atomic nuclei (the energies of such gamma rays range from ~1 keV to tens of MeV). During nuclear reactions (for example, during the annihilation of an electron and a positron, the decay of a neutral pion, etc.), as well as during the deflection of energetic charged particles in magnetic and electric fields.

Gamma rays, unlike b-rays and b-rays, are not deflected by electric and magnetic fields and are characterized by greater penetrating power at equal energies and other equal conditions. Gamma rays cause the ionization of atoms of a substance. The main processes that occur when gamma radiation passes through matter:

Photoelectric effect (a gamma quantum is absorbed by an electron of the atomic shell, transferring all the energy to it and ionizing the atom).

Compton scattering (a gamma quantum is scattered by an electron, transferring part of its energy to it).

The birth of electron-positron pairs (in the field of the nucleus, a gamma quantum with an energy of at least 2mec2 = 1.022 MeV is converted into an electron and a positron).

Photonuclear processes (at energies above several tens of MeV, a gamma quantum is capable of knocking nucleons out of the nucleus).

Gamma rays, like any other photons, can be polarized.

Irradiation with gamma quanta, depending on the dose and duration, can cause chronic and acute radiation sickness. Stochastic effects of radiation include various types of cancer. At the same time, gamma irradiation suppresses the growth of cancer and other rapidly dividing cells. Gamma radiation is a mutagenic and teratogenic factor.

A layer of substance can serve as protection against gamma radiation. The effectiveness of protection (that is, the probability of absorption of a gamma quantum when passing through it) increases with increasing thickness of the layer, density of the substance and the content of heavy nuclei in it (lead, tungsten, depleted uranium, etc.).

The unit of measurement for radioactivity is the becquerel (Bq). One becquerel equals one decay per second. The activity content of a substance is often assessed per unit weight of the substance (Bq/kg) or its volume (Bq/l, Bq/cubic m). A non-systemic unit is often used - the curie (Ci, Ci). One curie corresponds to the number of disintegrations per second in 1 gram of radium. 1 Ci = 3.7.1010 Bq.

The relationships between the units of measurement are shown in the table below.

The widely known non-systemic unit roentgen (P, R) is used to determine the exposure dose. One roentgen corresponds to a dose of x-ray or gamma radiation at which 2.109 pairs of ions are formed in 1 cm3 of air. 1 R = 2, 58.10-4 C/kg.

To evaluate the effect of radiation on a substance, the absorbed dose is measured, which is defined as the absorbed energy per unit mass. The unit of absorbed dose is called the rad. One rad is equal to 100 erg/g. The SI system uses another unit - the gray (Gy, Gy). 1 Gy = 100 rad = 1 J/kg.

The biological effect of different types of radiation is not the same. This is due to differences in their penetrating ability and the nature of energy transfer to the organs and tissues of a living organism. Therefore, to assess biological consequences, the biological equivalent of X-rays, the rem, is used. The dose in rem is equivalent to the dose in rad multiplied by the radiation quality factor. For X-rays, beta and gamma rays, the quality factor is considered equal to unity, that is, the rem corresponds to the rad. Alpha particles have a quality factor of 20 (meaning that alpha particles cause 20 times more damage to living tissue than the same absorbed dose of beta or gamma rays). For neutrons the coefficient ranges from 5 to 20 depending on the energy. The SI system introduces a special unit for the equivalent dose, called the sievert (Sv, Sv). 1 Sv = 100 rem. The equivalent dose in sieverts corresponds to the absorbed dose in grays multiplied by the quality factor.

2. Impact of radiation on the human body

There are two types of effects of ionizing radiation on the body: somatic and genetic. With a somatic effect, the consequences manifest themselves directly in the irradiated person, with a genetic effect - in his offspring. Somatic effects may be early or delayed. Early ones occur in the period from several minutes to 30-60 days after irradiation. These include redness and peeling of the skin, clouding of the lens of the eye, damage to the hematopoietic system, radiation sickness, and death. Long-term somatic effects appear several months or years after irradiation in the form of persistent skin changes, malignant neoplasms, decreased immunity, and shortened life expectancy.

When studying the effect of radiation on the body, the following features were identified:

b High efficiency of absorbed energy, even small amounts can cause profound biological changes in the body.

b The presence of a latent (incubation) period for the manifestation of the effects of ionizing radiation.

b The effects of small doses can be cumulative or cumulative.

b Genetic effect - impact on offspring.

Various organs of a living organism have their own sensitivity to radiation.

Not every organism (person) generally reacts the same way to radiation.

Exposure depends on the frequency of exposure. With the same dose of radiation, the lesser the harmful effects, the more dispersed it is received over time.

Ionizing radiation can affect the body through both external (especially x-rays and gamma radiation) and internal (especially alpha particles) irradiation. Internal irradiation occurs when sources of ionizing radiation enter the body through the lungs, skin and digestive organs. Internal irradiation is more dangerous than external irradiation, since sources of ionizing radiation that get inside expose unprotected internal organs to continuous irradiation.

Under the influence of ionizing radiation, water, which is an integral part of the human body, is split and ions with different charges are formed. The resulting free radicals and oxidants interact with the molecules of the organic matter of the tissue, oxidizing and destroying it. Metabolism is disrupted. Changes occur in the composition of the blood - the level of red blood cells, white blood cells, platelets and neutrophils decreases. Damage to the hematopoietic organs destroys the human immune system and leads to infectious complications.

Local lesions are characterized by radiation burns of the skin and mucous membranes. With severe burns, swelling, blisters form, and tissue death (necrosis) is possible.

Fatally absorbed and maximum permissible radiation doses.

Lethal absorbed doses for individual body parts are as follows:

b head - 20 Gy;

b lower abdomen - 50 Gy;

b chest -100 Gy;

limbs - 200 Gy.

When exposed to doses 100-1000 times higher than the lethal dose, a person may die during exposure ("death by ray").

Depending on the type of ionizing radiation, there may be different protective measures: reducing the exposure time, increasing the distance to sources of ionizing radiation, fencing sources of ionizing radiation, sealing sources of ionizing radiation, equipment and installation of protective equipment, organization of dosimetric monitoring, hygiene and sanitation measures.

A - personnel, i.e. persons who permanently or temporarily work with sources of ionizing radiation;

B - a limited part of the population, i.e. persons who are not directly involved in working with sources of ionizing radiation, but due to their living conditions or workplace location may be exposed to ionizing radiation;

B - the entire population.

The maximum permissible dose is the highest value of the individual equivalent dose per year, which, with uniform exposure over 50 years, will not cause adverse changes in the health of personnel that can be detected by modern methods.

Table 2. Maximum permissible radiation doses

Natural sources give a total annual dose of approximately 200 mrem (space - up to 30 mrem, soil - up to 38 mrem, radioactive elements in human tissues - up to 37 mrem, radon gas - up to 80 mrem and other sources).

Artificial sources add an annual equivalent radiation dose of approximately 150-200 mrem (medical devices and research - 100-150 mrem, watching TV - 1-3 mrem, coal-fired thermal power plants - up to 6 mrem, consequences of nuclear weapons tests - up to 3 mrem and others sources).

The World Health Organization (WHO) has determined the maximum permissible (safe) equivalent radiation dose for an inhabitant of the planet to be 35 rem, subject to its uniform accumulation over 70 years of life.

Table 3. Biological disorders during a single (up to 4 days) irradiation of the entire human body

Radiation dose, (Gy)	Degree of radiation sickness	Beginning of the primary reaction	Nature of the primary reaction	Consequences of radiation
Up to 0.250 - 1.0	There are no visible violations. Changes in the blood are possible. Changes in the blood, work ability is impaired
		After 2-3 hours	Mild nausea with vomiting. Passes on the day of irradiation	Typically 100% recovery even without treatment

3. Protection from ionizing radiation

Anti-radiation protection of the population includes: notification of radiation hazards, the use of collective and individual protective equipment, compliance with the rules of behavior of the population in areas contaminated with radioactive substances. Protection of food and water from radioactive contamination, use of medical personal protective equipment, determination of levels of contamination of the territory, dosimetric monitoring of public exposure and examination of contamination of food and water by radioactive substances.

According to the Civil Defense warning signals “Radiation Hazard,” the population must take shelter in protective structures. As is known, they significantly (several times) weaken the effect of penetrating radiation.

Due to the danger of radiation damage, it is impossible to begin providing first aid to the population if there are high levels of radiation in the area. In these conditions, the provision of self- and mutual assistance by the affected population itself, and strict adherence to the rules of conduct in the contaminated area are of great importance.

In areas contaminated with radioactive substances, you must not eat food, drink water from contaminated water sources, or lie down on the ground. The procedure for preparing food and feeding the population is determined by the Civil Defense authorities, taking into account the levels of radioactive contamination of the area.

To protect against air contaminated with radioactive particles, gas masks and respirators (for miners) can be used. There are also general protection methods such as:

b increasing the distance between the operator and the source;

b reduction of the duration of work in the radiation field;

b shielding of the radiation source;

b remote control;

b use of manipulators and robots;

ь full automation of the technological process;

b use of personal protective equipment and warning with a radiation hazard sign;

b constant monitoring of radiation levels and radiation doses to personnel.

Personal protective equipment includes an anti-radiation suit containing lead. The best absorber of gamma rays is lead. Slow neutrons are well absorbed by boron and cadmium. Fast neutrons are first slowed down using graphite.

The Scandinavian company Handy-fashions.com is developing protection against radiation from mobile phones, for example, it presented a vest, cap and scarf designed to protect against harmful radiation from mobile phones. For their production, special anti-radiation fabric is used. Only the pocket on the vest is made of ordinary fabric for stable signal reception. The cost of a complete protective kit starts from $300.

Protection against internal exposure consists of eliminating direct contact of workers with radioactive particles and preventing them from entering the air of the work area.

It is necessary to be guided by radiation safety standards, which specify the categories of exposed persons, dose limits and protection measures, and sanitary rules that regulate the placement of premises and installations, the place of work, the procedure for obtaining, recording and storing radiation sources, requirements for ventilation, dust and gas purification, neutralization radioactive waste, etc.

Also, to protect personnel premises, the Penza State Academy of Architecture and Construction is developing a “high-density mastic for radiation protection.” The composition of mastics includes: binder - resorcinol-formaldehyde resin FR-12, hardener - paraformaldehyde and filler - high-density material.

Protection from alpha, beta, gamma rays.

The basic principles of radiation safety are not to exceed the established basic dose limit, to exclude any unnecessary exposure and to reduce the radiation dose to the lowest possible level. In order to implement these principles in practice, radiation doses received by personnel when working with sources of ionizing radiation are necessarily monitored, work is carried out in specially equipped rooms, protection by distance and time is used, and various means of collective and individual protection are used.

To determine individual radiation doses to personnel, it is necessary to systematically carry out radiation (dosimetric) monitoring, the scope of which depends on the nature of work with radioactive substances. Each operator who has contact with sources of ionizing radiation is given an individual dosimeter1 to monitor the received dose of gamma radiation. In rooms where work with radioactive substances is carried out, it is necessary to ensure general control over the intensity of various types of radiation. These rooms must be isolated from other rooms and equipped with a supply and exhaust ventilation system with an air exchange rate of at least five. The painting of walls, ceilings and doors in these rooms, as well as the installation of the floor, are carried out in such a way as to prevent the accumulation of radioactive dust and to avoid the absorption of radioactive aerosols. Vapors and liquids from finishing materials (painting of walls, doors and in some cases ceilings should be done with oil paints, floors are covered with materials that do not absorb liquids - linoleum, polyvinyl chloride, etc.). All building structures in premises where work with radioactive substances is carried out must not have cracks or discontinuities; The corners are rounded to prevent the accumulation of radioactive dust in them and to facilitate cleaning. At least once a month, general cleaning of the premises is carried out with mandatory washing of walls, windows, doors, furniture and equipment with hot soapy water. Routine wet cleaning of premises is carried out daily.

To reduce personnel exposure, all work with these sources is carried out using long grips or holders. Time protection means that work with radioactive sources is carried out over such a period of time that the radiation dose received by personnel does not exceed the maximum permissible level.

Collective means of protection against ionizing radiation are regulated by GOST 12.4.120-83 “Means of collective protection against ionizing radiation. General requirements". In accordance with this regulatory document, the main means of protection are stationary and mobile protective screens, containers for transporting and storing sources of ionizing radiation, as well as for collecting and transporting radioactive waste, protective safes and boxes, etc.

Stationary and mobile protective screens are designed to reduce the level of radiation in the workplace to an acceptable level. If work with sources of ionizing radiation is carried out in a special room - a working chamber, then its walls, floor and ceiling, made of protective materials, serve as screens. Such screens are called stationary. To construct mobile screens, various shields are used that absorb or attenuate radiation.

Screens are made from various materials. Their thickness depends on the type of ionizing radiation, the properties of the protective material and the required radiation attenuation factor k. The value k shows how many times it is necessary to reduce the energy parameters of radiation (exposure dose rate, absorbed dose, particle flux density, etc.) in order to obtain acceptable values of the listed characteristics. For example, for the case of absorbed dose, k is expressed as follows:

where D is the absorbed dose rate; D0 is the permissible absorbed dose level.

For the construction of stationary means of protecting walls, floors, ceilings, etc. they use brick, concrete, barite concrete and barite plaster (they contain barium sulfate - BaSO4). These materials reliably protect personnel from exposure to gamma and x-ray radiation.

Various materials are used to create mobile screens. Protection against alpha radiation is achieved by using screens made of ordinary or organic glass several millimeters thick. A layer of air of several centimeters is sufficient protection against this type of radiation. To protect against beta radiation, screens are made of aluminum or plastic (plexiglass). Lead, steel, and tungsten alloys effectively protect against gamma and X-ray radiation. Viewing systems are made from special transparent materials, such as lead glass. Materials containing hydrogen (water, paraffin), as well as beryllium, graphite, boron compounds, etc., protect from neutron radiation. Concrete can also be used to protect against neutrons.

Protective safes are used to store gamma radiation sources. They are made of lead and steel.

To work with radioactive substances with alpha and beta activity, protective glove boxes are used.

Protective containers and collections for radioactive waste are made of the same materials as the screens - organic glass, steel, lead, etc.

When working with sources of ionizing radiation, the hazardous area must be limited by warning signs.

A danger zone is a space in which a worker may be exposed to hazardous and (or) harmful production factors (in this case, ionizing radiation).

The operating principle of devices designed to monitor personnel exposed to ionizing radiation is based on various effects that occur when this radiation interacts with matter. The main methods for detecting and measuring radioactivity are gas ionization, scintillation and photochemical methods. The most commonly used ionization method is based on measuring the degree of ionization of the medium through which radiation has passed.

Scintillation methods for detecting radiation are based on the ability of certain materials to absorb the energy of ionizing radiation and convert it into light radiation. An example of such a material is zinc sulfide (ZnS). A scintillation counter is a photoelectron tube with a window coated with zinc sulfide. When radiation enters this tube, a weak flash of light occurs, which leads to the appearance of electric current pulses in the photoelectron tube. These impulses are amplified and counted.

There are other methods for determining ionizing radiation, for example calorimetric, which are based on measuring the amount of heat released when radiation interacts with an absorbing substance.

Radiation monitoring devices are divided into two groups: dosimeters, used for quantitative measurement of dose rate, and radiometers or radiation indicators, used for the rapid detection of radioactive contamination.

Domestic devices used, for example, are dosimeters of the DRGZ-04 and DKS-04 brands. The first is used to measure gamma and x-ray radiation in the energy range 0.03-3.0 MeV. The instrument scale is calibrated in microroentgen/second (μR/s). The second device is used to measure gamma and beta radiation in the energy range 0.5-3.0 MeV, as well as neutron radiation (hard and thermal neutrons). The instrument scale is graduated in milliroentgens per hour (mR/h). The industry also produces household dosimeters intended for the population, for example, the Master-1 household dosimeter (designed to measure the dose of gamma radiation), the ANRI-01 household dosimeter-radiometer (Sosna).

nuclear radiation deadly ionizing

Conclusion

So, from the above we can draw the following conclusion:

Ionizing radiation- in the most general sense - various types of microparticles and physical fields capable of ionizing matter. The most significant types of ionizing radiation are: short-wave electromagnetic radiation (X-ray and gamma radiation), flows of charged particles: beta particles (electrons and positrons), alpha particles (nuclei of the helium-4 atom), protons, other ions, muons, etc. ., as well as neutrons. In nature, ionizing radiation is usually generated as a result of spontaneous radioactive decay of radionuclides, nuclear reactions (synthesis and induced fission of nuclei, capture of protons, neutrons, alpha particles, etc.), as well as during the acceleration of charged particles in space (the nature of such acceleration of cosmic particles to the end is not clear).

Artificial sources of ionizing radiation are artificial radionuclides (generate alpha, beta and gamma radiation), nuclear reactors (generate mainly neutron and gamma radiation), radionuclide neutron sources, particle accelerators (generate streams of charged particles, as well as bremsstrahlung photon radiation), X-ray machines (generate bremsstrahlung X-rays). Irradiation is very dangerous for the human body, the degree of danger depends on the dose (in my abstract I gave the maximum permissible standards) and the type of radiation - the safest is alpha radiation, and the more dangerous is gamma radiation.

Ensuring radiation safety requires a set of diverse protective measures, depending on the specific conditions of working with sources of ionizing radiation, as well as on the type of source.

Time protection is based on reducing the time spent working with the source, which makes it possible to reduce radiation doses to personnel. This principle is especially often used when personnel directly work with low levels of radioactivity.

Protection by distance is a fairly simple and reliable method of protection. This is due to the ability of radiation to lose its energy in interactions with matter: the greater the distance from the source, the greater the processes of interaction of radiation with atoms and molecules, which ultimately leads to a decrease in the radiation dose to personnel.

Shielding is the most effective way to protect against radiation. Depending on the type of ionizing radiation, various materials are used to make screens, and their thickness is determined by power and radiation.

Literature

1. “Harmful chemicals. Radioactive substances. Directory." Under general ed. L.A. Ilyina, V.A. Filov. Leningrad, "Chemistry". 1990.

2. Fundamentals of protecting the population and territories in emergency situations.” Ed. acad. V.V. Tarasova. Moscow University Publishing House. 1998.

3. Life safety / Ed. S.V. Belova. - 3rd ed., revised. - M.: Higher. school, 2001. - 485 p.

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Main characteristics

Ionizing radiation is a type of radiant energy that enters a specific environment, causing the process of ionization in the body. This characteristic of ionizing radiation is suitable for X-rays, radioactive and high energies, and much more.

Ionizing radiation has a direct effect on the human body. Despite the fact that ionizing radiation can be used in medicine, it is extremely dangerous, as evidenced by its characteristics and properties.

Well-known varieties are radioactive irradiations, which appear due to the arbitrary splitting of the atomic nucleus, which causes a transformation of chemical and physical properties. Substances that can decay are considered radioactive.

They can be artificial (seven hundred elements), natural (fifty elements) - thorium, uranium, radium. It should be noted that they have carcinogenic properties; toxins are released as a result of exposure to humans and can cause cancer and radiation sickness.

It is necessary to note the following types of ionizing radiation that affect the human body:

Alpha

They are considered positively charged helium ions, which appear in the event of the decay of the nuclei of heavy elements. Protection against ionizing radiation is carried out using a piece of paper or cloth.

Beta

– a flow of negatively charged electrons that appear in the event of the decay of radioactive elements: artificial, natural. The damaging factor is much higher than that of the previous species. As protection you will need a thick screen, more durable. Such radiations include positrons.

Gamma

- a hard electromagnetic oscillation that appears after the decay of nuclei of radioactive substances. A high penetrating factor is observed and is the most dangerous radiation of the three listed for the human body. To shield the rays, you need to use special devices. For this you will need good and durable materials: water, lead and concrete.

X-ray

Ionizing radiation is generated in the process of working with a tube and complex installations. The characteristic resembles gamma rays. The difference lies in the origin and wavelength. There is a penetrating factor.

Neutron

Neutron radiation is a stream of uncharged neutrons that are part of nuclei, except hydrogen. As a result of irradiation, substances receive a portion of radioactivity. There is the largest penetrating factor. All these types of ionizing radiation are very dangerous.

Main sources of radiation

Sources of ionizing radiation can be artificial or natural. The human body mainly receives radiation from natural sources, these include:

terrestrial radiation;
internal irradiation.

As for the sources of terrestrial radiation, many of them are carcinogenic. These include:

Uranus;
potassium;
thorium;
polonium;
lead;
rubidium;
radon.

The danger is that they are carcinogenic. Radon is a gas that has no odor, color, or taste. It is seven and a half times heavier than air. Its decay products are much more dangerous than gas, so the impact on the human body is extremely tragic.

Artificial sources include:

nuclear energy;
enrichment factories;
uranium mines;
burial grounds with radioactive waste;
X-ray machines;
nuclear explosion;
scientific laboratories;
radionuclides, which are actively used in modern medicine;
lighting devices;
computers and phones;
Appliances.

If these sources are nearby, there is a factor of the absorbed dose of ionizing radiation, the unit of which depends on the duration of exposure to the human body.

The operation of sources of ionizing radiation occurs every day, for example: when you work at a computer, watch a TV show or talk on a mobile phone or smartphone. All of these sources are to some extent carcinogenic and can cause severe and fatal diseases.

The placement of sources of ionizing radiation includes a list of important, responsible work related to the development of a project for the location of irradiation installations. All radiation sources contain a specific unit of radiation, each of which has a specific effect on the human body. This includes manipulations carried out for installation and commissioning of these installations.

It should be noted that disposal of sources of ionizing radiation is mandatory.

This is a process that helps decommission generation sources. This procedure consists of technical and administrative measures that are aimed at ensuring the safety of personnel, the population, and there is also an environmental protection factor. Carcinogenic sources and equipment are a huge danger to the human body, so they must be disposed of.

Features of radiation registration

The characteristics of ionizing radiation show that they are invisible, odorless and colorless, so they are difficult to notice.

For this purpose, there are methods for recording ionizing radiation. As for the methods of detection and measurement, everything is done indirectly, using some property as a basis.

The following methods for detecting ionizing radiation are used:

Physical: ionization, proportional counter, gas-discharge Geiger-Muller counter, ionization chamber, semiconductor counter.
Calorimetric detection method: biological, clinical, photographic, hematological, cytogenetic.
Luminescent: fluorescent and scintillation counters.
Biophysical method: radiometry, calculation.

Dosimetry of ionizing radiation is carried out using instruments; they are able to determine the radiation dose. The device includes three main parts - a pulse counter, a sensor, and a power source. Radiation dosimetry is possible thanks to a dosimeter or radiometer.

Effects on humans

The effect of ionizing radiation on the human body is especially dangerous. The following consequences are possible:

there is a factor of very profound biological change;
there is a cumulative effect of a unit of absorbed radiation;
the effect manifests itself over time, as there is a latent period;
all internal organs and systems have different sensitivity to a unit of absorbed radiation;
radiation affects all offspring;
the effect depends on the unit of radiation absorbed, the radiation dose, and duration.

Despite the use of radiation devices in medicine, their effects can be harmful. The biological effect of ionizing radiation in the process of uniform irradiation of the body, calculated at 100% of the dose, occurs as follows:

bone marrow – unit of absorbed radiation 12%;
lungs – at least 12%;
bones – 3%;
testes, ovaries– absorbed dose of ionizing radiation about 25%;
thyroid gland– absorbed dose unit about 3%;
mammary glands – approximately 15%;
other tissues - the unit of absorbed radiation dose is 30%.

As a result, various diseases can occur, including oncology, paralysis and radiation sickness. It is extremely dangerous for children and pregnant women, as abnormal development of organs and tissues occurs. Toxins and radiation are sources of dangerous diseases.

Humans are exposed to ionizing radiation everywhere. To do this, it is not necessary to get into the epicenter of a nuclear explosion; it is enough to be under the scorching sun or conduct an X-ray examination of the lungs.

Ionizing radiation is a flow of radiation energy generated during decay reactions of radioactive substances. Isotopes that can increase the radiation fund are found in the earth’s crust, in the air; radionuclides can enter the human body through the gastrointestinal tract, respiratory system and skin.

Minimum levels of background radiation do not pose a threat to humans. The situation is different if ionizing radiation exceeds permissible standards. The body will not immediately react to harmful rays, but years later pathological changes will appear that can lead to disastrous consequences, including death.

What is ionizing radiation?

The release of harmful radiation occurs after the chemical decay of radioactive elements. The most common are gamma, beta and alpha rays. When radiation enters the body, it has a destructive effect on humans. All biochemical processes are disrupted under the influence of ionization.

Types of radiation:

Alpha rays have increased ionization, but poor penetrating ability. Alpha radiation hits human skin, penetrating to a distance of less than one millimeter. It is a beam of released helium nuclei.
Electrons or positrons move in beta rays; in an air flow they are able to cover distances of up to several meters. If a person appears near the source, beta radiation will penetrate deeper than alpha radiation, but the ionizing ability of this species is much less.
One of the highest-frequency electromagnetic radiations is the gamma-ray variety, which has increased penetrating ability but very little ionizing effect.
characterized by short electromagnetic waves that arise when beta rays come into contact with matter.
Neutron - highly penetrating beams of rays consisting of uncharged particles.

Where does the radiation come from?

Sources of ionizing radiation can be air, water and food. Harmful rays occur naturally or are created artificially for medical or industrial purposes. There is always radiation in the environment:

comes from space and makes up a large part of the total percentage of radiation;
radiation isotopes are freely found in familiar natural conditions and are contained in rocks;
Radionuclides enter the body with food or by air.

Artificial radiation was created in the context of developing science; scientists were able to discover the uniqueness of X-rays, with the help of which it is possible to accurately diagnose many dangerous pathologies, including infectious diseases.

On an industrial scale, ionizing radiation is used for diagnostic purposes. People working at such enterprises, despite all the safety measures applied in accordance with sanitary requirements, are in harmful and dangerous working conditions that adversely affect their health.

What happens to a person when exposed to ionizing radiation?

The destructive effect of ionizing radiation on the human body is explained by the ability of radioactive ions to react with cell components. It is well known that eighty percent of man consists of water. When irradiated, water decomposes and hydrogen peroxide and hydrate oxide are formed in cells as a result of chemical reactions.

Subsequently, oxidation occurs in the organic compounds of the body, as a result of which the cells begin to collapse. After a pathological interaction, a person’s metabolism at the cellular level is disrupted. The effects can be reversible when exposure to radiation was insignificant, and irreversible with prolonged exposure.

The effect on the body can manifest itself in the form of radiation sickness, when all organs are affected; radioactive rays can cause gene mutations that are inherited in the form of deformities or severe diseases. There are frequent cases of degeneration of healthy cells into cancer cells with the subsequent growth of malignant tumors.

Consequences may not appear immediately after interaction with ionizing radiation, but after decades. The duration of the asymptomatic course directly depends on the degree and time during which the person received radiation exposure.

Biological changes under the influence of rays

Exposure to ionizing radiation entails significant changes in the body, depending on the extent of the area of skin exposed to radiation energy, the time during which the radiation remains active, as well as the condition of organs and systems.

To indicate the strength of radiation over a certain period of time, the unit of measurement is usually considered to be the Rad. Depending on the magnitude of the missed rays, a person may develop the following conditions:

up to 25 rad – general health does not change, the person feels good;
26 – 49 rad – the condition is generally satisfactory; at this dosage, the blood begins to change its composition;
50 – 99 rad – the victim begins to feel general malaise, fatigue, bad mood, pathological changes appear in the blood;
100 – 199 rad – the exposed person is in poor condition, most often the person cannot work due to deteriorating health;
200 – 399 rad – a large dose of radiation, which develops multiple complications and sometimes leads to death;
400 – 499 rad – half of the people who find themselves in a zone with such radiation values die from frolicking pathologies;
exposure to more than 600 rad does not give a chance for a successful outcome, a fatal disease takes the lives of all victims;
a one-time exposure to a dose of radiation that is thousands of times greater than the permissible figures - everyone dies directly during the disaster.

A person’s age plays a big role: children and young people under the age of twenty-five are most susceptible to the negative effects of ionizing energy. Receiving large doses of radiation during pregnancy can be compared with exposure in early childhood.

Brain pathologies occur only from the middle of the first trimester, from the eighth week to the twenty-sixth inclusive. The risk of cancer in the fetus increases significantly with unfavorable background radiation.

What are the dangers of being exposed to ionizing rays?

A one-time or regular exposure of radiation to the body tends to accumulate and cause subsequent reactions over a period of time from several months to decades:

inability to conceive a child, this complication develops in both women and men, making them sterile;
the development of autoimmune diseases of unknown etiology, in particular multiple sclerosis;
radiation cataracts leading to vision loss;
the appearance of a cancerous tumor is one of the most common pathologies with tissue modification;
diseases of an immune nature that disrupt the normal functioning of all organs and systems;
a person exposed to radiation lives much shorter;
the development of mutating genes that will cause serious developmental defects, as well as the appearance of abnormal deformities during fetal development.

Remote manifestations may develop directly in the exposed individual or be inherited and occur in subsequent generations. Directly at the sore spot through which the rays passed, changes occur in which the tissues atrophy and thicken with the appearance of multiple nodules.

This symptom can affect the skin, lungs, blood vessels, kidneys, liver cells, cartilage and connective tissue. Groups of cells become inelastic, harden and lose the ability to fulfill their purpose in the body of a person with radiation sickness.

Radiation sickness

One of the most dangerous complications, different stages of development of which can lead to the death of the victim. The disease can have an acute course with a one-time exposure to radiation or a chronic process with constant presence in the radiation zone. Pathology is characterized by persistent changes in all organs and cells and the accumulation of pathological energy in the patient’s body.

The disease manifests itself with the following symptoms:

general intoxication of the body with vomiting, diarrhea and elevated body temperature;
on the part of the cardiovascular system, the development of hypotension is noted;
a person gets tired quickly, collapses may occur;
with large doses of exposure, the skin turns red and becomes covered with blue spots in areas that lack oxygen supply, muscle tone decreases;
the second wave of symptoms is total hair loss, deterioration of health, consciousness remains slow, general nervousness, atony of muscle tissue, and disorders in the brain are observed, which can cause clouding of consciousness and cerebral edema.

How to protect yourself from radiation?

Determining effective protection from harmful rays is the basis for preventing human injury in order to avoid the occurrence of negative consequences. To save yourself from radiation exposure you must:

Reduce the time of exposure to isotope decay elements: a person should not stay in the danger zone for a long period. For example, if a person works in a hazardous industry, the worker’s stay in the place of energy flow should be reduced to a minimum.
To increase the distance from the source, this can be done by using multiple tools and automation tools that allow you to perform work at a considerable distance from external sources with ionizing energy.
It is necessary to reduce the area on which the rays will fall with the help of protective equipment: suits, respirators.

Ionizing radiation is electromagnetic radiation that is created during radioactive decay, nuclear transformations, inhibition of charged particles in matter and forms ions of different signs when interacting with the environment.

Interaction with matter of charged particles, gamma rays and x-rays. Corpuscular particles of nuclear origin (-parts, -particles, neutrons, protons, etc.), as well as photon radiation (quanta and X-ray and bremsstrahlung) have significant kinetic energy. Interacting with matter, they lose this energy mainly as a result of elastic interactions with atomic nuclei or electrons (as happens during the interaction of billiard balls), giving them all or part of their energy to excite atoms (i.e. transfer of an electron from a closer one to orbit more distant from the nucleus), as well as on the ionization of atoms or molecules of the medium (i.e., the separation of one or more electrons from atoms)

Elastic interaction is characteristic of neutral particles (trons) and photons that have no charge. In this case, the neutron, interacting with atoms, can, in accordance with the laws of classical mechanics, transfer a part of the energy proportional to the masses of the colliding particles. If it is a heavy atom, then only part of the energy is transferred. If it is a hydrogen atom equal to the mass of a neutron, then all the energy is transferred. In this case, the neutron slows down to thermal energies of the order of fractions of an electric volt and then enters into nuclear reactions. By striking an atom, a neutron can transfer to it such an amount of energy that is sufficient for the nucleus to “jump out” of the electron shell. In this case, a charged particle is formed with a significant speed, which is capable of ionizing the medium.

The interaction with matter and photon is similar. It is not capable of ionizing the medium on its own, but knocks out electrons from the atom, which ionize the medium. Neutrons and photon radiation are classified as indirectly ionizing radiation.

Charged particles (- and -particles), protons and others are capable of ionizing the medium due to interaction with the electric field of the atom and the electric field of the nucleus. In this case, charged particles are slowed down and deviate from the direction of their movement, emitting bremsstrahlung radiation, one of the types of photon radiation.

Charged particles can, due to inelastic interactions, transfer to the atoms of the medium an amount of energy that is insufficient for ionization. In this case, atoms are formed in an excited state, which transfer this energy to other atoms, or emit quanta of characteristic radiation, or, by colliding with other excited atoms, can receive energy sufficient to ionize the atoms.

As a rule, when radiation interacts with substances, all three types of consequences of this interaction occur: elastic collision, excitation and ionization. Using the example of the interaction of electrons with matter in Table. Figure 3.15 shows the relative share and energy lost by them to various interaction processes.

Table 3.15

Relative share of energy lost by electrons as a result of various interaction processes, %

Energy, eV	Elastic interaction	Excitation of atoms	Ionization

The ionization process is the most important effect on which almost all methods of dosimetry of nuclear radiation, especially indirect ionizing radiation, are based.

During the ionization process, two charged particles are formed: a positive ion (or an atom that has lost an electron from its outer shell) and a free electron. With each interaction, one or more electrons can be removed.

The true work of ionization of an atom is 10... 17 eV, i.e. This is how much energy is required to remove an electron from an atom. It has been experimentally established that the energy transferred to the formation of one pair of ions in the air is on average 35 eV for -particles and 34 eV for electrons, and approximately 33 eV for biological tissue matter. The difference is determined as follows. The average energy used to form one pair of ions is determined experimentally as the ratio of the energy of the primary particle to the average number of ion pairs formed by one particle along its entire path. Since charged particles spend their energy on the processes of excitation and ionization, the experimental value of ionization energy includes all types of energy losses related to the formation of one pair of ions. Experimental confirmation of this is the table. 3.14.

Radiation doses. When ionizing radiation passes through a substance, it is affected only by that part of the radiation energy that is transferred to the substance and is absorbed by it. The portion of energy transferred by radiation to a substance is called a dose.

A quantitative characteristic of the interaction of ionizing radiation with a substance is the absorbed dose. Absorbed dose D (J/kg) is the ratio of the average energy He transferred by ionizing radiation to a substance in an elementary volume to the unit mass dm of the substance in this volume

In the SI system, the unit of absorbed dose is the gray (Gy), named after the English physicist and radiobiologist L. Gray. 1 Gy corresponds to the absorption of an average of 1 J of ionizing radiation energy in a mass of matter equal to 1 kg. 1 Gy = 1 Jkg -1.

Dose equivalent H - absorbed dose in an organ or tissue multiplied by the appropriate weighting factor for a given radiation, W R

where D T,R is the average absorbed dose in an organ or tissue T, W R is the weighting factor for radiation R. If the radiation field consists of several radiations with different values of W R, the equivalent dose is determined as:

The unit of measurement for equivalent dose is Jkg. -1, which has a special name sievert (Sv).

Effective dose E is a value used as a measure of the occurrence of long-term consequences of irradiation of the entire human body and its individual organs, taking into account their radiosensitivity. It represents the sum of the products of the equivalent dose in an organ by the corresponding coefficient for a given organ or tissue:

where is the equivalent dose in tissue T over time, and W T is the weighing factor for tissue T. The unit of measurement for the effective dose is Jkg -1, which has a special name - sievert (Sv).

The effective collective dose S is a value that determines the total effect of radiation on a group of people, defined as:

where is the average effective dose of the i-th subgroup of a group of people, is the number of people in the subgroup.

The unit of measurement for the effective collective dose is man-sievert (man-Sv).

The mechanism of biological action of ionizing radiation. The biological effect of radiation on a living organism begins at the cellular level. A living organism consists of cells. An animal cell consists of a cell membrane surrounding a gelatinous mass - the cytoplasm, which contains a denser nucleus. Cytoplasm consists of organic protein compounds that form a spatial lattice, the cells of which are filled with water, salts dissolved in it and relatively small molecules of lipids - substances with properties similar to fats. The nucleus is considered the most sensitive vital part of the cell, and its main structural elements are chromosomes. The structure of chromosomes is based on the dioxyribonucleic acid (DNA) molecule, which contains the hereditary information of the organism. Individual sections of DNA responsible for the formation of a certain elementary trait are called genes or “building blocks of heredity.” Genes are located on chromosomes in a strictly defined order, and each organism has a specific set of chromosomes in each cell. In humans, each cell contains 23 pairs of chromosomes. During cell division (mitosis), chromosomes are duplicated and arranged in a certain order in the daughter cells.

Ionizing radiation causes chromosome breakage (chromosomal aberrations), followed by the joining of broken ends into new combinations. This leads to a change in the gene apparatus and the formation of daughter cells that are different from the original ones. If persistent chromosomal aberrations occur in germ cells, this leads to mutations, i.e. the appearance of offspring with other characteristics in irradiated individuals. Mutations are useful if they lead to an increase in the vitality of the organism, and harmful if they manifest themselves in the form of various congenital defects. Practice shows that when exposed to ionizing radiation, the likelihood of beneficial mutations occurring is low.

However, in any cell, continuously operating processes are found to correct chemical damage in DNA molecules. It also turned out that DNA is quite resistant to breaks caused by radiation. It is necessary to make seven destructions of the DNA structure so that it can no longer be restored, i.e. only in this case does mutation occur. With fewer breaks, the DNA is restored to its original form. This indicates the high strength of genes in relation to external influences, including ionizing radiation.

The destruction of molecules vital for the body is possible not only through their direct destruction by ionizing radiation (target theory), but also through indirect action, when the molecule itself does not directly absorb radiation energy, but receives it from another molecule (solvent), which initially absorbed this energy . In this case, the radiation effect is due to the secondary influence of the products of radiolysis (decomposition) of the solvent on DNA molecules. This mechanism is explained by the theory of radicals. Repeated direct hits of ionizing particles into the DNA molecule, especially into its sensitive areas - genes, can cause its disintegration. However, the probability of such hits is less than that of water molecules, which serve as the main solvent in the cell. Therefore, radiolysis of water, i.e. the decay under the influence of radiation on hydrogen (H and hydroxyl (OH) radicals with the subsequent formation of molecular hydrogen and hydrogen peroxide is of paramount importance in radiobiological processes. The presence of oxygen in the system enhances these processes. Based on the theory of radicals, ions play a major role in the development of biological changes and radicals that are formed in water along the trajectory of ionizing particles.

The high ability of radicals to enter into chemical reactions determines the processes of their interaction with biologically important molecules located in close proximity to them. In such reactions, the structures of biological substances are destroyed, and this in turn leads to changes in biological processes, including the processes of formation of new cells.

Consequences of human exposure to ionizing radiation. When a mutation occurs in a cell, it spreads to all the cells of the new organism formed by division. In addition to genetic effects that can affect subsequent generations (congenital deformities), so-called somatic (bodily) effects are also observed, which are dangerous not only for the given organism itself (somatic mutation), but also for its offspring. A somatic mutation extends only to a certain circle of cells formed by normal division from a primary cell that has undergone a mutation.

Somatic damage to the body by ionizing radiation is the result of the effect of radiation on a large complex - groups of cells that form certain tissues or organs. Radiation inhibits or even completely stops the process of cell division, in which their life actually manifests itself, and strong enough radiation ultimately kills cells. The destructive effect of radiation is especially noticeable in young tissues. This circumstance is used, in particular, to protect the body from malignant (for example, cancerous tumors) tumors, which are destroyed under the influence of ionizing radiation much faster than benign cells. Somatic effects include local damage to the skin (radiation burn), eye cataracts (clouding of the lens), damage to the genitals (short-term or permanent sterilization), etc.

Unlike somatic ones, genetic effects of radiation are difficult to detect, since they act on a small number of cells and have a long latent period, measured in tens of years after irradiation. Such a danger exists even with very weak radiation, which, although it does not destroy cells, can cause chromosome mutations and change hereditary properties. Most of these mutations appear only when the embryo receives chromosomes from both parents that are damaged in the same way. The results of mutations, including mortality from hereditary effects - the so-called genetic death, were observed long before people began to build nuclear reactors and use nuclear weapons. Mutations can be caused by cosmic rays, as well as the natural background radiation of the Earth, which, according to experts, accounts for 1% of human mutations.

It has been established that there is no minimum level of radiation below which mutation does not occur. The total number of mutations caused by ionizing radiation is proportional to population size and average radiation dose. The manifestation of genetic effects depends little on the dose rate, but is determined by the total accumulated dose, regardless of whether it was received in 1 day or 50 years. It is believed that genetic effects do not have a dose threshold. Genetic effects are determined only by the effective collective dose of man-sievert (person-Sv), and detection of the effect in an individual is practically unpredictable.

Unlike genetic effects, which are caused by small doses of radiation, somatic effects always begin from a certain threshold dose: at lower doses, damage to the body does not occur. Another difference between somatic damage and genetic damage is that the body is able to overcome the effects of radiation over time, while cellular damage is irreversible.

The values of some doses and effects of radiation on the body are given in Table. 3.16.

Table 3.16

Radiation exposure and related biological effects

Impact
	Dose rate or duration	Irradiation	Biological effect
	In a week		Virtually absent
	Daily (for several years)		Leukemia
	One time		Chromosomal abnormalities in tumor cells (culture of relevant tissues)
	In a week		Virtually absent
	Accumulation of small doses		Doubling mutagenic effects in one generation
	One time
			SD 50 for people
			Hair loss (reversible)
	0.1-0.5 Sv/day		Treatment possible in hospital
	3 Sv/day or accumulation of small doses		Radiation cataract
			The occurrence of cancer of highly radiosensitive organs
			The occurrence of cancer of moderately radiosensitive organs
			Dose limit for nerve tissue
			Dose limit for the gastrointestinal tract

Note. О - total body irradiation; L - local irradiation; SD 50 is a dose leading to 50% mortality among persons exposed to radiation.

Standardization of exposure to ionizing radiation. The main legal standards in the field of radiation safety include the Radiation Safety Standards (NRB-99). The document belongs to the category of sanitary rules (SP 2.6.1.758-99), approved by the State Sanitary Doctor of the Russian Federation on July 2, 1999.

Radiation safety standards include terms and definitions that must be used in solving radiation safety problems. They also establish three classes of standards: basic dose limits; permissible levels, which are derived from dose limits; limits of annual intake, volumetric permissible average annual intake, specific activities, permissible levels of contamination of working surfaces, etc.; control levels.

The regulation of ionizing radiation is determined by the nature of the impact of ionizing radiation on the human body. In this case, two types of effects related to diseases in medical practice are distinguished: deterministic threshold effects (radiation sickness, radiation burn, radiation cataract, fetal development abnormalities, etc.) and stochastic (probabilistic) non-threshold effects (malignant tumors, leukemia, hereditary diseases) .

Ensuring radiation safety is determined by the following basic principles:

1. The principle of rationing is not to exceed the permissible limits of individual exposure doses to citizens from all sources of ionizing radiation.
2. The principle of justification is the prohibition of all types of activities involving the use of sources of ionizing radiation, in which the benefit obtained for humans and society does not exceed the risk of possible harm caused in addition to the natural background radiation exposure.
3. The optimization principle is to maintain at the lowest possible and achievable level, taking into account economic and social factors, individual radiation doses and the number of exposed persons when using any source of ionizing radiation.

For the purpose of socio-economic assessment of the impact of ionizing radiation on people to calculate the probabilities of losses and justify the costs of radiation protection when implementing the optimization principle NRB-99, it is introduced that exposure to a collective effective dose of 1 person-Sv leads to the loss of 1 person-year of life population.

NRB -- 99 introduces the concepts of individual and collective risk, and also determines the value of the maximum value of the level of negligible risk of exposure to radiation. According to these standards, the individual and collective lifetime risk of stochastic (probabilistic) effects are determined accordingly

where r, R are individual and collective lifetime risk, respectively; E - individual effective dose; -- probability for the i-th individual to receive an annual effective dose from E to E + dE; r E -- lifelong risk coefficient of reduction in the duration of a full life period by an average of 15 years, one stochastic effect (from fatal cancer, serious hereditary effects and non-fatal cancer, reduced in harm to the consequences of fatal cancer), equal

for occupational exposure:

1/person-Sv at mSv/year

for public exposure:

1/person-Sv at mSv/year;

1/person-Sv at mSv/year

For the purposes of radiation safety when exposed to radiation throughout the year, the individual risk of reducing the duration of a full life as a result of the occurrence of severe consequences from deterministic effects is conservatively assumed to be equal to:

where is the probability for the i-th individual to be irradiated with a dose greater than D when handling a source during the year; D is the threshold dose for a deterministic effect.

Potential exposure of a group of N individuals is justified if

where is the average reduction in the duration of a full life as a result of the occurrence of stochastic effects, equal to 15 years; -- average reduction in the duration of a full life as a result of the occurrence of severe consequences from deterministic effects, equal to 45 years; -- monetary equivalent of the loss of 1 person-year of life of the population; V-- income from production; P -- costs of main production, excluding damage from protection; Y -- damage from protection.

NRB-99 emphasizes that risk reduction to the lowest possible level (optimization) should be carried out taking into account two circumstances:

- the risk limit regulates potential exposure from all possible sources. Therefore, for each source during optimization, a risk limit is established;
- when reducing the risk of potential exposure, there is a minimum level of risk below which the risk is considered negligible and further risk reduction is inappropriate.

The individual risk limit for man-made exposure of personnel is assumed to be 1.010 -3 per 1 year, and for the population 5.010 -5 per 1 year.

The level of negligible risk separates the area of risk optimization and the area of unconditionally acceptable risk and is 10 -6 for 1 year.

NRB-99 introduces the following categories of exposed persons:

- personnel and persons working with man-made sources (group A) or who, due to working conditions, are in the sphere of their influence (group B);
- the entire population, including personnel, outside the scope and conditions of their production activities.

Table 3.17

Basic dose limits

Notes. * Radiation doses, like all other permissible derived levels for group B personnel, should not exceed 1/4 of the values for group A personnel.

** Refers to the average value in a 5 mg/cm2 thick layer under a 5 mg/cm2 thick cover layer. On the palms the thickness of the coating layer is 40 mg/cm2.

The main dose limits for exposed personnel and the public do not include doses from natural, medical sources of ionizing radiation and doses due to radiation accidents. There are special restrictions on these types of exposure.

NRB--99 stipulate that with simultaneous exposure to sources of external and internal irradiation, the condition must be met that the ratio of the external irradiation dose to the dose limit and the ratio of annual nuclide intakes to their limits in total do not exceed 1.

For female personnel under the age of 45 years, the equivalent dose in the skin on the surface of the lower abdomen should not exceed 1 mSv per month, and the intake of radionuclides into the body during the year should not exceed 1/20 of the annual intake limit for personnel. In this case, the equivalent radiation dose to the fetus for 2 months of undetected pregnancy does not exceed 1 mSv.

When it is discovered that female employees are pregnant, employers must transfer them to another job that does not involve radiation.

For students under the age of 21 who are exposed to sources of ionizing radiation, the annual accumulated doses should not exceed the values established for members of the public.

When conducting preventive medical x-ray scientific studies of practically healthy individuals, the annual effective radiation dose should not exceed 1 mSv.

NRB-99 also establishes requirements for limiting exposure of the population in conditions of a radiation accident.