Types of ionizing radiation. Physics of ionizing radiation

Atomic radiation is one of the most dangerous. Its consequences are unpredictable for humans. What is meant by the concept of radioactivity? What do the words “more” or “less” radioactivity mean? What particles are included in the composition? various types atomic radiation?

What is radioactive radiation?

Radioactive radiation can contain various particles. However, all three types of radiation belong to the same category - they are called ionizing. What does this term mean? The energy of the radiation is incredibly high - so much so that when the radiation reaches a particular atom, it knocks an electron out of its orbit. Then the atom that has become the target of radiation turns into an ion, which is positively charged. That is why atomic radiation is called ionizing, no matter what type it belongs to. High power distinguishes ionizing radiation from other types, such as microwave or infrared.

How does ionization occur?

To understand what may be part of radioactive radiation, it is necessary to consider the ionization process in detail. It happens as follows. When magnified, an atom looks like a small poppy seed (the nucleus of an atom), surrounded by the orbits of its electrons, like a shell soap bubble. When radioactive decay occurs, a tiny particle is emitted from this nucleus - an alpha or beta particle. When a charged particle is emitted, it changes and this means that a new chemical substance is formed.

The particles that make up radioactive radiation behave as follows. The grain that flies away from the nucleus rushes forward with gigantic speed. On its way, it can crash into the shell of another atom and knock out an electron from it in the same way. As already mentioned, such an atom will turn into a charged ion. However, in this case, the substance will remain the same, since the number of protons in the nucleus remains unchanged.

Features of the radioactive decay process

Knowledge of the listed processes allows us to estimate how intensively radioactive decay occurs. This value is measured in becquerels. For example, if one decay occurs per second, then they say: “The activity of the isotope is 1 becquerel.” At one time, a unit called the curie was used instead of this unit. It was equal to 37 billion becquerels. In this case, it is necessary to compare the activity of the same amount of substance. The activity of a certain unit mass of an isotope is called specific activity. This value is inversely proportional to a particular isotope.

Characteristics of radioactive radiation. Their sources

Ionizing radiation can occur not only in the event of radioactive decay. The following can serve as sources of radioactive radiation: fission reaction (occurs as a result of an explosion or inside nuclear reactor), the synthesis of so-called light nuclei (occurs on the surface of the Sun, other stars, as well as in a hydrogen bomb), as well as various All these sources of radiation have one common feature - a very powerful level of energy.

What particles make up alpha type radioactive radiation?

The differences between the three types of ionizing radiation - alpha, beta and gamma - lie in their nature. When these radiations were discovered, no one had any idea what they could be. Therefore, they were simply called letters of the Greek alphabet.

As their name suggests, alpha rays were the first to be discovered. They were part of radioactive radiation during the decay of heavy isotopes such as uranium or thorium. Their nature was determined by the passage of time. Scientists have found that alpha radiation is quite heavy. In the air it cannot travel even a few centimeters. It turned out that radioactive radiation may include nuclei of helium atoms. This is exactly what applies to alpha radiation.

Its main source is radioactive isotopes. In other words, it represents positively charged “sets” of two protons and the same number of neutrons. In this case, they say that the composition of radioactive radiation includes A-particles, or alpha particles. Two protons and two neutrons form a helium nucleus, which is characterized by alpha radiation. For the first time in mankind, such a reaction was achieved by E. Rutherford, who was engaged in the transformation of nitrogen nuclei into oxygen nuclei.

Beta radiation, discovered later, but no less dangerous

Then it turned out that radioactive radiation could include not only helium nuclei, but also just ordinary electrons. This is true for beta radiation - it consists of electrons. But their speed is much greater than the speed of alpha radiation. This type of radiation also has less charge than alpha radiation. Beta particles “inherit” different charges and different speeds from the parent atom.

It can reach from 100 thousand km/sec up to the speed of light. But in open air, beta radiation can spread several meters. Their penetrating ability is very low. Beta rays cannot penetrate paper, fabric, or thin sheets of metal. They only penetrate into this matter. However, unprotected exposure can cause skin or eye burns, as does ultraviolet rays.

Negatively charged beta particles are called electrons, and positively charged ones are called positrons. Large amounts of beta radiation are very dangerous for humans and can lead to radiation sickness. Ingestion of radionuclides can be much more dangerous.

Gamma radiation: composition and properties

Gamma radiation was discovered next. In this case, it turned out that radioactive radiation may contain photons with a certain wavelength. Gamma radiation is similar to ultraviolet, infrared rays and radio waves. In other words, it represents electromagnetic radiation, however, the energy of the photons entering it is very high.

This type of radiation has an extremely high ability to penetrate any obstacle. The denser the material standing in the path of this ionizing radiation, the better it can block dangerous gamma rays. For this role, lead or concrete is most often chosen. In the open air, gamma radiation can easily travel hundreds and thousands of kilometers. If it affects a person, it leads to damage to the skin and internal organs. In its properties, gamma radiation can be compared with x-rays. But they differ in their origin. After all, X-ray radiation is obtained only under artificial conditions.

What radiation is the most dangerous?

Many of those who have already studied what rays make up radioactive radiation are convinced of the dangers of gamma rays. After all, they can easily travel many kilometers, destroying people’s lives and leading to terrible radiation sickness. It is in order to protect themselves from gamma rays that nuclear reactors are surrounded by huge concrete walls. Small pieces of isotopes are always placed in containers made of lead. However, the main danger to humans is

The dose is the amount that is usually calculated based on a person's body weight. For example, a dose of 2 mg of medication would be appropriate for one patient. For another, the same dose may have an adverse effect. The dose of radioactive radiation is also assessed. Its danger is determined by the absorbed dose. To determine it, the amount of radiation that has been absorbed by the body is first measured. And then this amount is compared with body weight.

Radiation dose is a criterion of its danger

Different types of radiation can cause different harm to living organisms. Therefore, the penetrating ability of various types of radioactive radiation and their damaging effects should not be confused. For example, when a person has no way to protect himself from radiation, alpha radiation turns out to be much more dangerous than gamma rays. After all, it contains heavy hydrogen nuclei. And this type, such as alpha radiation, shows its danger only when it enters the body. Then internal irradiation occurs.

So, radioactive radiation can contain three types of particles: helium nuclei, ordinary electrons, and photons with a certain wavelength. The danger of a particular type of radiation is determined by its dose. The origin of these rays does not matter. For a living organism, it makes absolutely no difference where the radiation comes from: be it an X-ray machine, the Sun, a nuclear power plant, a radon resort, or an explosion. The most important thing is how many dangerous particles were absorbed.

Where does atomic radiation come from?

Along with the natural radiation background, human civilization is forced to exist among many artificially made sources of dangerous ionizing radiation. Most often it is a consequence terrible accidents. For example, the disaster at the Fukushima-1 nuclear power plant in September 2013 led to a leak of radioactive water. As a result, the content of strontium and cesium isotopes in environment has grown exponentially.

Ionizing radiation- fluxes of photons, as well as charged or neutral particles, the interaction of which with the substance of the environment leads to its ionization. Ionization plays an important role in the development of radiation-induced effects, especially in living tissue. The average energy consumption for the formation of one pair of ions depends relatively little on the type ionizing radiation, which makes it possible to judge by the degree of ionization of a substance about the energy transferred to it. For registration and analysis ionizing radiation instrumental methods also use ionization.

Sources ionizing radiation divided into natural (natural) and artificial. Natural sources ionizing radiation are space and radioactive substances common in nature (radionuclides). In space, cosmic radiation is formed and reaches the Earth - corpuscular flows of ionizing radiation. Primary cosmic radiation consists of charged particles and high-energy photons. In the Earth's atmosphere, primary cosmic radiation is partially absorbed and initiates nuclear reactions, as a result of which radioactive atoms are formed, which themselves emit radiation. , therefore cosmic radiation at the surface of the Earth differs from primary cosmic radiation. There are three main types of cosmic radiation: galactic cosmic radiation, solar cosmic radiation and the Earth's radiation belts. Galactic cosmic radiation is the most high-energy component of the corpuscular flow in interplanetary space and represents the nuclei of chemical elements (mainly hydrogen and helium) accelerated to high energies; In terms of its penetrating ability, this type of cosmic radiation surpasses all types ionizing radiation, except for neutrinos. To completely absorb galactic cosmic radiation, a lead shield about 15 mm thick would be required. m. Solar cosmic radiation is the high-energy part of the corpuscular radiation of the Sun and occurs during chromospheric flares during the day. During the period of intense solar flares The flux density of solar cosmic radiation can be thousands of times higher than the normal flux density of galactic cosmic radiation. Solar cosmic radiation consists of protons, helium nuclei and heavier nuclei. High-energy solar protons pose the greatest danger to humans in space flight conditions (see. Space biology and medicine). The Earth's radiation belts were formed in near-Earth space due to primary cosmic radiation and partial capture of its charged component magnetic field Earth. The Earth's radiation belts consist of charged particles: electrons in the electron belt and protons in the proton belt. The radiation field is established in the radiation belts. increased intensity, which is taken into account when launching manned spacecraft.

Natural, or natural, radionuclides have different origins; some of them belong to radioactive families, the ancestors of which (uranium, thorium) have been part of the rocks that make up our planet since the period of its formation; Some of the natural radionuclides are the product of activation of stable isotopes by cosmic radiation. A distinctive property of radionuclides is radioactivity, i.e. spontaneous transformation (decay) of atomic nuclei, leading to a change in their atomic number and (or) mass number. The rate of radioactive decay, which characterizes the activity of a radionuclide, is equal to the number of radioactive transformations per unit time.

The unit of radioactivity is defined by the International System of Units (SI) as the becquerel ( Bk); 1 Bk equal to one decay per second. In practice, the extra-systemic unit of activity curie ( Ki); 1 Ki is equal to 3.7 × 10 10 decays per second, i.e. 3.7× 10 10 Bk. As a result of radioactive transformations, charged and neutral particles arise, forming the radiation field.

According to the type of particles included in the composition ionizing radiation, there are alpha radiation, beta radiation, gamma radiation, X-ray radiation, neutron radiation, proton radiation, etc. X-ray and gamma radiation are classified as photon, or electromagnetic, ionizing radiation, and all other types ionizing radiation- to corpuscular. Photons are “portions” (quanta) of electromagnetic radiation. Their energy is expressed in electron volts. It is tens of thousands of times greater than the energy of a visible light quantum.

Alpha radiation is a stream of alpha particles, or nuclei of helium atoms, carrying a positive charge equal to two elementary units of charge. Alpha particles are highly ionizing particles that quickly lose their energy when interacting with matter. For this reason, alpha radiation is weakly penetrating and in medical practice it is used either to irradiate the surface of the body, or an alpha-emitting radionuclide is injected directly into the pathological focus during interstitial radiation therapy.

Beta radiation is a stream of negatively charged electrons or positively charged positrons emitted during beta decay. Beta particles are weakly ionizing particles; however, compared to alpha particles at the same energy, they have greater penetrating power.

Neutron radiation is a stream of electrically neutral particles (neutrons) that arise in some nuclear reactions during the interaction of high-energy elementary particles with matter, as well as during the fission of heavy nuclei. Neutrons transfer part of their energy to the nuclei of atoms of the medium and initiate nuclear reactions. As a result, charged particles of various types appear in the substance irradiated by the neutron flux, which ionize the substance of the medium; radionuclides can also be formed. The properties of neutron radiation and the nature of its interaction with living tissue are determined by the energy of neutrons.

Some types ionizing radiation arise in nuclear power and nuclear physics installations; nuclear reactors, charged particle accelerators, X-ray machines, and artificial radionuclides also created using these means.

proton radiation is generated in special accelerators. The eye is a stream of protons - particles that carry a single positive charge and have a mass close to the mass of neutrons. Protons are highly ionizing particles; Being accelerated to high energies, they are capable of penetrating relatively deeply into the matter of the medium. This makes it possible to effectively use proton radiation in remote radiation therapy.

Electron radiation is generated by special electron accelerators (for example, betatrons, linear accelerators) if a beam of accelerated electrons is output outside. These same accelerators can be a source of bremsstrahlung radiation - a type of photon radiation that occurs when accelerated electrons are decelerated in the substance of a special accelerator target. X-ray radiation used in medical radiology is also bremsstrahlung from electrons accelerated in an x-ray tube.

Gamma radiation is a stream of high-energy photons emitted during the decay of radionuclides; widely used in radiation therapy of malignant tumors. There are directed and non-directed I. and. If all directions of propagation ionizing radiation are equivalent, then they talk about isotropic I. and. By the nature of distribution over time I. and. can be continuous or pulsed.

To describe the field of I. and. use physical quantities that determine the spatiotemporal distribution of radiation in the medium. The most important characteristics fields I. and. are the particle flux density and the energy flux density. In general, the particle flux density is the number of particles penetrating per unit time into an elementary sphere, divided by the cross-sectional area of ​​this sphere. Energy flux density I. and. is synonymous with the commonly used term “radiation intensity”. It is equal to the particle flux density multiplied by the average energy of one particle, and characterizes the speed of energy transfer. The unit of measurement of intensity of I. and. in the SI system is J/m 2 × s.

Biological effects of ionizing radiation. Under the biological action of And. and. understand the diverse reactions that occur in an irradiated biological object, ranging from the primary processes of radiation energy exchange to the effects that appear long after radiation exposure. Knowledge of mechanisms of biological action ionizing radiation necessary for the urgent adoption of adequate measures to ensure the radiation safety of personnel and the population during accidents at nuclear power plants and other nuclear industry enterprises. To ionize most of the elements that make up a biological substrate, a fairly large amount of energy is needed - 10-15 eV, called the ionization potential. Because particles and photons ionizing radiation have energies ranging from tens to millions eV, which far exceeds the energy of intra- and intermolecular bonds of molecules and substances that make up any biological substrate, then all living things are subject to damaging radiation effects.

The most simplified scheme initial stages radiation damage is as follows. Following and essentially simultaneously with the transfer of energy and. atoms and molecules of the irradiated environment (the physical stage of the biological action of radiation) primary radiation-chemical processes develop in it, which are based on two mechanisms: direct, when the molecules of a substance experience changes during direct interaction with ionizing radiation, and indirect, in which the molecules being changed do not directly absorb energy ionizing radiation, but receive it by transfer from other molecules. As a result of these processes, free radicals and other highly reactive products are formed, leading to changes in vital macromolecules, and ultimately to the final biological effect. In the presence of oxygen, radiation-chemical processes are intensified (oxygen effect), which, other things being equal, helps to enhance the biological effect of oxygen and. (cm. Radio modification, Radiomodifying agents). It should be borne in mind that changes in the irradiated substrate are not necessarily final and irreversible. Usually, final result cannot be predicted in each specific case, since along with radiation damage, restoration of the original state may also occur.

Impact ionizing radiation on a living organism is usually called irradiation, although this is not entirely accurate, because irradiation of the body can be carried out by any other type of non-ionizing radiation (visible light, infrared, ultraviolet, high-frequency radiation, etc.). The effectiveness of irradiation depends on the time factor, which is understood as the distribution ionizing radiation doses in time. The most effective is single acute irradiation at a high dose rate of I. and. Prolonged chronic or intermittent (fractionated) irradiation at a given dose has less biological effect due to the processes post-radiation recovery.

A distinction is made between external and internal irradiation. With external irradiation, the source of I. and. is located outside the body, and when internal (incorporated) it is carried out by radionuclides that enter the body through the respiratory system, gastrointestinal tract or through damaged skin.

Biological action ionizing radiation largely depends on its quality, mainly determined by linear energy transfer (LET) - the energy lost by a particle per unit length of its path in the medium. Depending on the LET value, everything ionizing radiation divided into rarely ionizing (LET less than 10 keV/µm) and densely ionizing (LET more than 10 keV/µm). Impact by different types ionizing radiation in equal absorbed doses leads to effects of different magnitudes. To quantify the quality of radiation, the concept of relative biological effectiveness (RBE) has been introduced, which is usually assessed by comparing the dose of the studied radiation. , causing a certain biological effect, with a dose of standard And. and. , causing the same effect. Conventionally, we can assume that RBE depends only on LET and increases with the latter.

At whatever level - tissue, organ, systemic or organismal - the biological action of And. and is considered. , its effect is always determined by the action of And. and. at the cell level. Detailed study of reactions initiated in the cell ionizing radiation, is the subject of fundamental research radiobiology. It should be noted that most reactions excited ionizing radiation, including such a universal reaction as a delay in cell division, is temporary, transient and does not affect the viability of the irradiated cell. Reactions of this type - reversible reactions - also include various metabolic disorders, incl. inhibition of nucleic acid metabolism and oxidative phosphorylation, chromosome adhesion, etc. The reversibility of this type of radiation reactions is explained by the fact that they are a consequence of damage to part of multiple structures, the loss of which is very quickly replenished or simply goes unnoticed. Hence the characteristic feature of these reactions: with an increase in the dose of I. and. It is not the proportion of reacting individuals (cells) that increases, but the magnitude and degree of reaction (for example, the duration of the division delay) of each irradiated cell.

The effects that lead an irradiated cell to death - lethal radiation reactions - have a significantly different nature. In radiobiology, cell death refers to the loss of a cell's ability to divide. On the contrary, “surviving” cells are those that have retained the ability to reproduce (cloning).

There are two forms of lethal reactions that are fatal to dividing and poorly differentiated cells: interphase, in which the cell dies soon after irradiation, at least before the onset of the first mitosis, and reproductive, when the affected cell does not die immediately after exposure to radiation. , and in the process of division. The most common reproductive form of lethal reactions. The main cause of cell death in this case is structural damage to chromosomes caused by radiation. These damages are easily detected by cytological examination of cells at different stages of mitosis and take the form of chromosomal rearrangements, or chromosomal aberrations. Due to incorrect connection of chromosomes and simply the loss of their terminal fragments during division, the descendants of such a damaged cell will undoubtedly die immediately after this division or as a result of two or three subsequent mitoses (depending on the significance of the lost genetic material for the viability of the cell). The occurrence of structural damage to chromosomes is a process of probability, mainly associated with the formation of double breaks in the DNA molecule, i.e. with irreparable damage to vital cellular macromolecules. In this regard, in contrast to the reversible cellular reactions discussed above, with an increase in the dose of I. and. the number (proportion) of cells with lethal genome damage increases, strictly described for each type of cell in “dose-effect” coordinates. Currently, special methods have been developed for isolating clonogenic cells from various tissues in vivo and growing them in vitro, with the help of which, after constructing the appropriate dose survival curves, the radiosensitivity of the organs being studied and the possibility of its change in the desired direction are quantitatively assessed. In addition, counting the number of cells with chromosomal aberrations on special preparations is used for biological dosimetry to assess the radiation situation, for example on board spaceship, as well as to determine the severity and prognosis of acute radiation sickness.

The described radiation reactions of cells underlie the immediate effects that appear in the first hours, days, weeks and months after general irradiation of the body or local irradiation of individual body segments. These include, for example, erythema, radiation dermatitis, various manifestations of acute radiation sickness (leukopenia, bone marrow aplasia, hemorrhagic syndrome, intestinal lesions), sterility (temporary or permanent, depending on the dose ionizing radiation).

After a long time (months and years) after irradiation, long-term consequences of local and general radiation exposure develop. These include a reduction in life expectancy, the occurrence of malignant neoplasms and radiation cataracts. Pathogenesis of long-term effects of irradiation in to a greater extent associated with damage to tissues characterized by a low level of proliferative activity, which make up the majority of animal and human organs. In-depth knowledge of mechanisms of biological action ionizing radiation necessary, on the one hand, to develop methods radiation protection and pathogenetic treatment of radiation injuries, and on the other hand, to find ways to specifically enhance radiation exposure during radiation genetic work and other aspects of radiation biotechnology or during radiation therapy of malignant neoplasms using radiomodifying agents. In addition, understanding the mechanisms of biological action ionizing radiation necessary for a doctor in case of emergency taking adequate measures to ensure radiation safety of personnel and the population during accidents at nuclear power plants and other nuclear industry enterprises.

Bibliography: Gozenbuk V.L. and others. Dose load on humans in fields of gamma-neutron radiation, M., 1978; Ivanov V.I. Dosimetry course, M., 1988; Keirim-Marcus I.B. Equidosimetry, M., 1980; Komar V.E. and Hanson K.P. Information macromolecules in radiation damage to cells, M., 1980; Moiseev A.A. and Ivanov V.I. Handbook of dosimetry and radiation hygiene, M., 1984; Yarmonenko S.P. Radiobiology of humans and animals, M., 1988.

Ionizing radiation- a type of radiation that everyone associates exclusively with explosions of atomic bombs and accidents at nuclear power plants.

However, in reality, ionizing radiation surrounds a person and represents a natural background radiation: it is formed in household appliances, on electrical towers, etc. When exposed to sources, a person is exposed to this radiation.

Should I be afraid of serious consequences - radiation sickness or organ damage?

The strength of the radiation depends on the duration of contact with the source and its radioactivity. Household appliances that create minor “noise” are not dangerous to humans.

But some types of sources can cause serious harm to the body. To prevent negative effects, you need to know basic information: what ionizing radiation is and where it comes from, as well as how it affects humans.

Ionizing radiation occurs when radioactive isotopes decay.

There are many such isotopes; they are used in electronics, the nuclear industry, and energy production:

1. uranium-238;
2. thorium-234;
3. uranium-235, etc.

Radioactive isotopes decay naturally over time. The decay rate depends on the type of isotope and is calculated in half-life.

After a certain period of time (for some elements this can be several seconds, for others it can be hundreds of years), the number of radioactive atoms is reduced by exactly half.

The energy that is released during the decay and destruction of nuclei is released in the form of ionizing radiation. It penetrates various structures, knocking out ions from them.

Ionizing waves are based on gamma radiation, measured in gamma rays. During the transfer of energy, no particles are released: atoms, molecules, neutrons, protons, electrons or nuclei. The effect of ionizing radiation is purely wave.

Penetrating power of radiation

All types vary in penetrating ability, that is, the ability to quickly cover distances and pass through various physical barriers.

Alpha radiation has the lowest rate, and ionizing radiation is based on gamma rays - the most penetrating of the three types of waves. In this case, alpha radiation has the most negative effect.

What makes gamma radiation different?

It is dangerous due to the following characteristics:

• travels at the speed of light;
• passes through soft fabrics, wood, paper, drywall;
• stopped only by a thick layer of concrete and a metal sheet.

To delay the waves that propagate this radiation, special boxes are installed at nuclear power plants. Thanks to them, radiation cannot ionize living organisms, that is, disrupt the molecular structure of people.

On the outside, the boxes are made of thick concrete, inner part upholstered with a sheet of pure lead. Lead and concrete reflect rays or trap them in their structure, preventing them from spreading and harming the living environment.

Types of radiation sources

The opinion that radiation occurs only as a result of human activity is erroneous. Almost all living objects and the planet itself have a weak background radiation. Therefore, it is very difficult to avoid ionizing radiation.

Based on the nature of occurrence, all sources are divided into natural and anthropogenic. The most dangerous are anthropogenic ones, such as the release of waste into the atmosphere and water bodies, an emergency situation or the action of an electrical appliance.

The danger of the latter source is controversial: small emitting devices are not considered to pose a serious threat to humans.

The action is individual: someone may feel a deterioration in their health against the background of weak radiation, while another individual will be completely unaffected by the natural background.

Natural sources of radiation

Mineral rocks pose the main danger to humans. Accumulates in their cavities greatest number radioactive gas, radon, invisible to human receptors.

It is naturally released from the earth's crust and is poorly recorded by testing instruments. When supplying building materials, contact with radioactive rocks is possible, and as a result, the process of ionization of the body.

You should be wary of:

1. granite;
2. pumice;
3. marble;
4. phosphogypsum;
5. alumina

These are the most porous materials that best retain radon. This gas is released from building materials or soil.

It is lighter than air, so it rises to great heights. If, instead of the open sky, an obstacle is found above the ground (canopy, roof of a room), the gas will accumulate.

High saturation of air with its elements leads to irradiation of people, which can only be compensated for by removing radon from residential areas.

To get rid of radon, you need to start simple ventilation. You should try not to inhale the air in the room where the infection occurred.

Registration of the occurrence of accumulated radon is carried out only with the help of specialized symptoms. Without them, a conclusion about the accumulation of radon can only be made on the basis of non-specific reactions of the human body (headache, nausea, vomiting, dizziness, darkening of the eyes, weakness and burning).

If radon is detected, a team from the Ministry of Emergency Situations is called to eliminate the radiation and check the effectiveness of the procedures performed.

Sources of anthropogenic origin

Another name for man-made sources is man-made. The main source of radiation is nuclear power plants located around the world. Staying in station areas without protective clothing leads to the onset of serious illnesses and death.

At a distance of several kilometers from the nuclear power plant, the risk is reduced to zero. With proper insulation, all ionizing radiation remains inside the station, and you can be in close proximity to the work area without receiving any radiation dose.

In all spheres of life, you can encounter a radiation source, even if you don’t live in a city near a nuclear power plant.

Artificial ionizing radiation is widely used in various industries:

• medicine;
• industry;
• agriculture;
• knowledge-intensive industries.

However, it is impossible to receive radiation from devices that are manufactured for these industries.

The only thing that is acceptable is the minimum penetration of ion waves, which does not cause harm when short duration impact.

Fallout

A serious problem of our time associated with recent tragedies at nuclear power plants is the spread of radioactive rain. Emissions of radiation into the atmosphere result in the accumulation of isotopes in the atmospheric liquid - clouds. When there is an excess of liquid, precipitation begins, which poses a serious threat to crops and humans.

The liquid is absorbed into agricultural lands where rice, tea, corn, and cane grow. These crops are typical for the eastern part of the planet, where the problem of radioactive rain is most pressing.

Ion radiation has less of an impact on other parts of the world because precipitation does not reach Europe and the island nations in the UK area. However, in the USA and Australia, rain sometimes exhibits radiation properties, so you need to be careful when purchasing fruits and vegetables from there.

Radioactive fallout can fall over bodies of water, and then the liquid can enter residential buildings through water treatment channels and water supply systems. Treatment facilities do not have equipment sufficient to reduce radiation. There is always a risk that the water you take is ionic.

How to protect yourself from radiation

A device that measures whether there is ion radiation in the background of a product is freely available. It can be purchased for little money and used to check purchases. The name of the testing device is dosimeter.

It is unlikely that a housewife will check purchases directly in the store. Shyness in front of strangers usually gets in the way. But at least at home, those products that came from areas prone to radioactive rain need to be checked. It is enough to bring the counter to the object, and it will show the level of emission of dangerous waves.

The effect of ionizing radiation on the human body

It has been scientifically proven that radiation has a negative effect on humans. This was also found out from real experience: unfortunately, accidents on Chernobyl nuclear power plant, in Hiroshima, etc. proven biological and radiation.

The effects of radiation are based on the “dose” received—the amount of energy transferred. A radionuclide (wave-emitting element) can have an effect both inside and outside the body.

The dose received is measured in conventional units - Grays. It must be taken into account that the dose may be equal, but the effect of radiation may be different. This is due to the fact that different radiations cause reactions of different strengths (the most pronounced for alpha particles).

The strength of the impact is also affected by which part of the body the waves hit. The genitals and lungs are most susceptible to structural changes, the thyroid gland is less susceptible.

The result of biochemical influence

Radiation affects the structure of the body's cells, causing biochemical changes: disturbances in circulation chemical substances and in body functions. The influence of waves appears gradually, and not immediately after irradiation.

If a person is exposed to the permissible dose (150 rem), then the negative effects will not be pronounced. With greater irradiation, the ionization effect increases.

Natural radiation is approximately 44 rem per year, with a maximum of 175. The maximum number is only slightly outside the normal range and does not cause negative changes in the body, except for headaches or mild nausea in hypersensitive people.

Natural radiation is based on the background radiation of the Earth, the consumption of contaminated products, and the use of technology.

If the proportion is exceeded, the following diseases develop:

1. genetic changes in the body;
2. sexual dysfunction;
3. brain cancers;
4. thyroid dysfunction;
5. cancer of the lungs and respiratory system;
6. radiation sickness.

Radiation sickness is the extreme stage of all radionuclide-related diseases and manifests itself only in those who are in the accident zone.

“People’s attitude towards a particular danger is determined by how well they know it.”

This material is a generalized answer to numerous questions that arise from users of devices for detecting and measuring radiation in domestic conditions.
Minimal use of specific terminology of nuclear physics when presenting the material will help you to freely navigate this environmental problem, without succumbing to radiophobia, but also without excessive complacency.

The danger of RADIATION, real and imaginary

“One of the first natural radioactive elements discovered was called radium.”
- translated from Latin - emitting rays, radiating.”

Each person in the environment is exposed to various phenomena that influence him. These include heat, cold, magnetic and ordinary storms, heavy rains, heavy snowfalls, strong winds, sounds, explosions, etc.

Thanks to the presence of sense organs assigned to him by nature, he can quickly respond to these phenomena with the help of, for example, a sunshade, clothing, shelter, medicine, screens, shelters, etc.

However, in nature there is a phenomenon to which a person, due to the lack of the necessary sense organs, cannot instantly react - this is radioactivity. Radioactivity is not a new phenomenon; Radioactivity and accompanying radiation (so-called ionizing) have always existed in the Universe. Radioactive materials are part of the Earth and even humans are slightly radioactive, because... Radioactive substances are present in the smallest quantities in any living tissue.

The most unpleasant property of radioactive (ionizing) radiation is its effect on the tissues of a living organism, therefore, appropriate measuring instruments are needed that would provide prompt information for making useful decisions before a long time has passed and undesirable or even fatal consequences appear. will not begin to feel immediately, but only after some time has passed. Therefore, information about the presence of radiation and its power must be obtained as early as possible.
However, enough of the mysteries. Let's talk about what radiation and ionizing (i.e. radioactive) radiation are.

Ionizing radiation

Any medium consists of tiny neutral particles - atoms, which consist of positively charged nuclei and negatively charged electrons surrounding them. Each atom is like a miniature solar system: “planets” move in orbit around a tiny nucleus - electrons.
Atomic nucleus consists of several elementary particles - protons and neutrons, held together by nuclear forces.

Protons particles having a positive charge equal in absolute value to the charge of electrons.

Neutrons neutral particles with no charge. The number of electrons in an atom is exactly equal to the number of protons in the nucleus, so each atom is generally neutral. The mass of a proton is almost 2000 times the mass of an electron.

The number of neutral particles (neutrons) present in the nucleus can be different if the number of protons is the same. Such atoms having nuclei with the same number protons, but differing in the number of neutrons, refer to varieties of the same chemical element, called "isotopes" of that element. To distinguish them from each other, a number is assigned to the symbol of the element equal to the sum of all particles in the nucleus of a given isotope. So uranium-238 contains 92 protons and 146 neutrons; Uranium 235 also has 92 protons, but 143 neutrons. All isotopes of a chemical element form a group of “nuclides”. Some nuclides are stable, i.e. do not undergo any transformations, while others emitting particles are unstable and turn into other nuclides. As an example, let's take the uranium atom - 238. From time to time, a compact group of four particles breaks out of it: two protons and two neutrons - an “alpha particle (alpha)”. Uranium-238 thus turns into an element whose nucleus contains 90 protons and 144 neutrons - thorium-234. But thorium-234 is also unstable: one of its neutrons turns into a proton, and thorium-234 turns into an element with 91 protons and 143 neutrons in its nucleus. This transformation also affects the electrons (beta) moving in their orbits: one of them becomes, as it were, superfluous, without a pair (proton), so it leaves the atom. The chain of numerous transformations, accompanied by alpha or beta radiation, ends with a stable lead nuclide. Of course, there are many similar chains of spontaneous transformations (decays) of different nuclides. The half-life is the period of time during which the initial number of radioactive nuclei on average decreases by half.
With each act of decay, energy is released, which is transmitted in the form of radiation. Often an unstable nuclide finds itself in an excited state, and the emission of a particle does not lead to complete removal of excitation; then it emits a portion of energy in the form of gamma radiation (gamma quantum). As with X-rays (which differ from gamma rays only in frequency), no particles are emitted. The entire process of spontaneous decay of an unstable nuclide is called radioactive decay, and the nuclide itself is called a radionuclide.

Different types of radiation are accompanied by the release of different amounts of energy and have different penetrating powers; therefore, they have different effects on the tissues of a living organism. Alpha radiation is blocked, for example, by a sheet of paper and is practically unable to penetrate the outer layer of the skin. Therefore, it does not pose a danger until radioactive substances emitting alpha particles enter the body through open wound, with food, water or inhaled air or steam, for example, in a bath; then they become extremely dangerous. The beta particle has greater penetrating ability: it penetrates the body tissue to a depth of one to two centimeters or more, depending on the amount of energy. The penetrating power of gamma radiation, which travels at the speed of light, is very high: only a thick lead or concrete slab can stop it. Ionizing radiation is characterized by a number of measurable physical quantities. These should include energy quantities. At first glance, it may seem that they are sufficient for recording and assessing the impact of ionizing radiation on living organisms and humans. However, these energy values ​​do not reflect the physiological effects of ionizing radiation on the human body and other living tissues; they are subjective and different for different people. Therefore, average values ​​are used.

Sources of radiation can be natural, present in nature, and independent of humans.

It has been established that of all natural sources of radiation, the greatest danger is radon, a heavy gas without taste, smell, and at the same time invisible; with its subsidiary products.

Radon is released from the earth's crust everywhere, but its concentration in the outside air varies significantly from place to place. globe. Paradoxical as it may seem at first glance, a person receives the main radiation from radon while in a closed, unventilated room. Radon concentrates in the air indoors only when they are sufficiently isolated from the external environment. Seeping through the foundation and floor from the soil or, less commonly, being released from building materials, radon accumulates indoors. Sealing rooms for the purpose of insulation only makes matters worse, since this makes it even more difficult for radioactive gas to escape from the room. The radon problem is especially important for low-rise buildings with carefully sealed rooms (to retain heat) and the use of alumina as an additive to building materials (the so-called “Swedish problem”). The most common building materials - wood, brick and concrete - emit relatively little radon. Granite, pumice, products made from alumina raw materials, and phosphogypsum have much greater specific radioactivity.

Another, usually less important, source of radon indoors is water and natural gas used for cooking and heating homes.

The concentration of radon in commonly used water is extremely low, but water from deep wells or artesian wells contains very high levels of radon. However, the main danger does not come from drinking water, even with a high radon content. Typically, people consume most of their water in food and hot drinks, and when boiling water or cooking hot food, radon disappears almost completely. A much greater danger is the ingress of water vapor with a high radon content into the lungs along with inhaled air, which most often occurs in the bathroom or steam room (steam room).

Radon enters natural gas underground. As a result of preliminary processing and during the storage of gas before it reaches the consumer, most of the radon evaporates, but the concentration of radon in the room can increase noticeably if kitchen stoves and other heating gas appliances are not equipped with an exhaust hood. In the presence of supply and exhaust ventilation, which communicates with the outside air, radon concentration does not occur in these cases. This also applies to the house as a whole - based on the readings of radon detectors, you can set a ventilation mode for the premises that completely eliminates the threat to health. However, given that the release of radon from the soil is seasonal, it is necessary to monitor the effectiveness of ventilation three to four times a year, avoiding exceeding the radon concentration standards.

Other sources of radiation, which unfortunately have potential dangers, are created by man himself. Sources of artificial radiation are artificial radionuclides, beams of neutrons and charged particles created with the help of nuclear reactors and accelerators. They are called man-made sources of ionizing radiation. It turned out that along with its dangerous nature for humans, radiation can be used to serve humans. This is not a complete list of areas of application of radiation: medicine, industry, agriculture, chemistry, science, etc. A calming factor is the controlled nature of all activities related to the production and use of artificial radiation.

The tests of nuclear weapons in the atmosphere, accidents at nuclear power plants and nuclear reactors and the results of their work, manifested in radioactive fallout and radioactive waste. However, only emergencies, such as the Chernobyl accident, can have an uncontrollable effect on humans.
The rest of the work is easily controlled at a professional level.

When radioactive fallout occurs in some areas of the Earth, radiation can enter the human body directly through agricultural products and food. It is very simple to protect yourself and your loved ones from this danger. When buying milk, vegetables, fruits, herbs, and any other products, it is not superfluous to turn on the dosimeter and bring it to the purchased product. Radiation is not visible - but the device will instantly detect the presence radioactive contamination. This is our life in the third millennium - a dosimeter becomes an attribute of everyday life, like a handkerchief, toothbrush, and soap.

IMPACT OF IONIZING RADIATION ON BODY TISSUE

The damage caused in a living organism by ionizing radiation will be greater, the more energy it transfers to tissues; the amount of this energy is called a dose, by analogy with any substance entering the body and completely absorbed by it. The body can receive a dose of radiation regardless of whether the radionuclide is located outside the body or inside it.

The amount of radiation energy absorbed by irradiated body tissues, calculated per unit mass, is called the absorbed dose and is measured in Grays. But this value does not take into account the fact that for the same absorbed dose, alpha radiation is much more dangerous (twenty times) than beta or gamma radiation. The dose recalculated in this way is called the equivalent dose; it is measured in units called Sieverts.

It should also be taken into account that some parts of the body are more sensitive than others: for example, given the same equivalent dose of radiation, cancer is more likely to occur in the lungs than in thyroid gland, and irradiation of the gonads is especially dangerous due to the risk of genetic damage. Therefore, human radiation doses should be taken into account with different coefficients. By multiplying the equivalent doses by the corresponding coefficients and summing them over all organs and tissues, we obtain an effective equivalent dose, reflecting the total effect of radiation on the body; it is also measured in Sieverts.

Charged particles.

Alpha and beta particles penetrating into the tissues of the body lose energy due to electrical interactions with the electrons of the atoms near which they pass. (Gamma rays and X-rays transfer their energy to matter in several ways, which ultimately also lead to electrical interactions.)

Electrical interactions.

Within a time of about ten trillionths of a second after the penetrating radiation reaches the corresponding atom in the tissue of the body, an electron is torn off from this atom. The latter is negatively charged, so the rest of the initially neutral atom becomes positively charged. This process is called ionization. The detached electron can further ionize other atoms.

Physico-chemical changes.

Both the free electron and the ionized atom usually cannot remain in this state for long and, over the next ten billionths of a second, participate in a complex chain of reactions that result in the formation of new molecules, including such extremely reactive ones as “free radicals.”

Chemical changes.

Over the next millionths of a second, the resulting free radicals react both with each other and with other molecules and, through a chain of reactions not yet fully understood, can cause chemical modification of biologically important molecules necessary for the normal functioning of the cell.

Biological effects.

Biochemical changes can occur within seconds or decades after irradiation and cause immediate cell death or changes in them.

For information, and not to intimidate, especially people who decide to devote themselves to working with ionizing radiation, you should know the maximum permissible doses. The units of measurement of radioactivity are given in Table 1. According to the conclusion of the International Commission on Radiation Protection in 1990, harmful effects can occur at equivalent doses of at least 1.5 Sv (150 rem) received during the year, and in cases of short-term exposure - at doses higher 0.5 Sv (50 rem). When radiation exposure exceeds a certain threshold, radiation sickness occurs. There are chronic and acute (with a single massive exposure) forms of this disease. Acute radiation sickness is divided into four degrees by severity, ranging from a dose of 1-2 Sv (100-200 rem, 1st degree) to a dose of more than 6 Sv (600 rem, 4th degree). Stage 4 can be fatal.

The doses received under normal conditions are negligible compared to those indicated. The equivalent dose rate generated by natural radiation ranges from 0.05 to 0.2 μSv/h, i.e. from 0.44 to 1.75 mSv/year (44-175 mrem/year).
For medical diagnostic procedures - x-rays, etc. - a person receives approximately another 1.4 mSv/year.

Since radioactive elements are present in brick and concrete in small doses, the dose increases by another 1.5 mSv/year. Finally, due to emissions from modern coal-fired thermal power plants and when flying on an airplane, a person receives up to 4 mSv/year. In total, the existing background can reach 10 mSv/year, but on average does not exceed 5 mSv/year (0.5 rem/year).

Such doses are completely harmless to humans. The dose limit in addition to the existing background for a limited part of the population in areas of increased radiation is set at 5 mSv/year (0.5 rem/year), i.e. with a 300-fold reserve. For personnel working with sources of ionizing radiation, the maximum permissible dose is set at 50 mSv/year (5 rem/year), i.e. 28 µSv/h with a 36-hour work week.

According to hygienic standards NRB-96 (1996), permissible dose rate levels for external irradiation of the whole body from man-made sources for permanent residence of personnel are 10 μGy/h, for residential premises and areas where members of the public are permanently located - 0 .1 µGy/h (0.1 µSv/h, 10 µR/h).

HOW DO YOU MEASURE RADIATION?

A few words about registration and dosimetry of ionizing radiation. Exist various methods registration and dosimetry: ionization (associated with the passage of ionizing radiation in gases), semiconductor (in which the gas is replaced solid body), scintillation, luminescent, photographic. These methods form the basis of the work dosimeters radiation. Gas-filled ionizing radiation sensors include ionization chambers, fission chambers, proportional counters, and Geiger-Muller counters. The latter are relatively simple, the cheapest, and not critical to operating conditions, which led to their widespread use in professional dosimetric equipment designed to detect and evaluate beta and gamma radiation. When the sensor is a Geiger-Muller counter, any ionizing particle that enters the sensitive volume of the counter causes a self-discharge. Precisely falling into the sensitive volume! Therefore, alpha particles are not registered, because they can't get in there. Even when registering beta particles, it is necessary to bring the detector closer to the object to make sure that there is no radiation, because in the air, the energy of these particles may be weakened, they may not penetrate the device body, will not enter the sensitive element and will not be detected.

Doctor of Physical and Mathematical Sciences, Professor at MEPhI N.M. Gavrilov
The article was written for the company "Kvarta-Rad"

Prof. Davydov A.V.

1. General information and terminology.

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

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

Ionizing radiation is divided into photon and corpuscular.

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

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

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

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

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

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

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

Closed source of ionizing radiation(sealed source) - in which the radioactive material is enclosed in a shell (ampule or protective coating) that prevents personnel contact with the radioactive material and its release into the environment above permissible levels under the conditions of use and wear for which it is designed.

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

By purpose There are calibration (model), control (working) and industrial (technological) sources.

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

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

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

Technical characteristics of radiation sources:

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

GOST R 51873-2002 - Closed sources of ionizing radiation. Are common technical requirements. Entered into force in 2003. The standard applies to sealed radionuclide sources of alpha, beta, gamma, x-ray and neutron radiation. Does not apply to model and control sources, as well as to sources in which the activity of radionuclides does not exceed the minimum significant level established by the “Radiation Safety Standards”.

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

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

The sources are non-renewable industrial products and cannot be repaired. If the radiation parameters are maintained within limits that satisfy the user, the seal is maintained and there are no defects, the service life of the source can be extended. The procedure for renewal is established by the authorities government controlled use of atomic energy.

Units of measurement of radioactivity and radiation doses.

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

Ionizing radiation dose is the amount of ionizing radiation energy that is perceived by some environment over a certain period of time.

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

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

Exposure dose (D exp) serves to characterize photon radiation and determines the degree of ionization of air under the influence of these rays. It is equal to the dose of radiation at which ions carrying an electrical charge of 1 coulomb (C) appear in 1 kg of atmospheric air. D exp = C/kg. The non-systemic unit is the roentgen (R). 1 P = 2.58 10 -4 C/kg.

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

Radon-222, a decay product of Ra-226, deserves special attention. It is an inert gas and is released from any environment and objects (soil, building materials, etc.), which almost always contain uranium and its decay products. The average radon concentration at ground level outdoors is 8 Bq/m 3 . Radon has a half-life of 3,824 days and can accumulate in closed and poorly ventilated areas.

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

2. Sources of charged particles.

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

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

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

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

Alpha particles, which have a large mass, when colliding with electrons of atomic shells experience very small deviations from their original direction and move almost linearly. The ranges of alpha particles in matter are very small. For example, an alpha particle with an energy of 4 MeV has a path length of approximately 2.5 cm in air, and hundredths of a millimeter in water or in the soft tissues of animals and humans.

Sources of beta radiation.

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

Beta decay of radionuclides is accompanied by neutrino radiation, and the division of decay energy between electron and neutrino is random. This leads to the fact that the energy distribution of emitted beta particles is continuous from 0 to the maximum energy E max determined for each isotope, the distribution mode is shifted to the region of low energies, and the average particle energy is of the order of (0.25-0.45) E max. An example of the energy distribution of beta radiation is shown in Fig. 1.

Fig 1. Example of beta radiation energy distribution

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

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

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

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

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

Table 1. Radionuclide sources of beta particles.

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

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

Unlike isotope sources with a continuous spectrum of electrons, accelerators produce a beam of electrons of a fixed energy, and the electron flow and energy can vary over wide intervals.

Fig 2. Accelerator ELV-8 (Novosibirsk)

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

Sources of alpha radiation.

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

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

Table 2. Radionuclide sources of alpha particles.

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

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

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

3. Sources of electromagnetic (photon) radiation.

Sources of gamma radiation.

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

The flow of gamma quanta has wave and corpuscular properties and propagates at the speed of light. The high penetrating ability of gamma radiation is explained by the absence of an electrical charge and a significant energy reserve. The intensity of gamma ray exposure decreases in inverse proportion to the square of the distance from the point source.

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

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

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

Table 3. Radionuclide sources of gamma radiation.

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

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

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

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

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

X-ray sources.

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

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

Table 4. Radionuclide sources of low-energy quanta.

Protection against X-ray radiation is much simpler than protection against gamma radiation. A 1 mm lead layer provides a tenfold attenuation of radiation with an energy of 100 keV.

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

An X-ray tube consists of a glass vacuum cylinder with soldered electrodes - a cathode, heated to a high temperature, and an anode. Electrons emitted by the cathode are accelerated in the space between the electrodes by a strong electric field (up to 500 kV for high-power tubes) and bombard the anode. When electrons hit the anode, their kinetic energy is partially converted into the energy of characteristic and bremsstrahlung radiation. The efficiency of X-ray tubes usually does not exceed 3%. Since most of the kinetic energy of electrons is converted into heat, the anode is made of a metal with high thermal conductivity, and a target made of a material with a high atomic number, such as tungsten, is applied to its surface (at 45 o to the electron flow) in the flow focusing zone. For powerful X-ray tubes, forced cooling of the anode is used (with water or a special solution). The specific power dissipated by the anode in modern tubes is from 10 to 10 4 W/mm 2.

Fig 3. X-ray tube radiation spectrum

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

4. Neutron sources.

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

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

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

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

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

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

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

The most well-known ampoule sources are radium-beryllium and polonium-beryllium. Polonium-210 is an almost pure alpha emitter. The decay of polonium is accompanied by gamma radiation of low intensity. The main disadvantage is the short service life, determined by the half-life of polonium.

The California Neutron Source uses a spontaneous nuclear reaction that releases a neutron from a nucleus, accompanied by intense gamma radiation. Each nuclear fission releases four neutrons. 1 g of source per second emits 2.4 * 10 12 neutrons, which corresponds to the neutron flux of an average nuclear reactor. The sources have a constant flow of neutrons (no monitoring required), “point-specific” radiation, a long service life (more than three years), and a relatively low cost.

Thermal neutron sources are designed in a similar way and additionally contain a graphite moderator case.

Table 5. Radionuclide neutron sources.

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

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

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

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

Most of the released energy is carried away by the neutron. The distribution of neutron energy is quite narrow and practically monoenergetic over the emission angles. The neutron yield is about 10 8 per 1 microcoulomb of deuterons. Neutron tubes operate, as a rule, in a pulsed mode, and the output power can exceed 10 12 n/s.

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

5. Inventory and disposal of sources

Radionuclide sources of ionizing radiation pose a potential danger to the population for the following reasons:

1. They are distributed across many organizations, and the normal life cycle of sources is not carried out everywhere (acquisition - accounting - control - use - disposal).

2. Sources of ionizing radiation cannot be provided with reliable protection.

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

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

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

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

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

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

Reducing the radiation dose when it is necessary to work with a source of ionizing radiation can be done in three ways: increasing the distance from the source, reducing the time spent near the source, and installing a screen that absorbs radiation. As you move away from a point source, the radiation dose decreases in inverse proportion to the square of the distance.