Elements of dosimetry of ionizing radiation. Dosimetry and radiometry of ionizing radiation Dosimetry of ionizing radiation

1. Dosimetry. Radiation doses. Dose rate.

2. Biological effects of radiation doses. Limit doses.

3. Dosimetric instruments. Ionizing radiation detectors.

4. Methods of protection against ionizing radiation.

5. Basic concepts and formulas.

6. Tasks.

34.1. Dosimetry. Radiation doses. Dose rate

The need to quantify the effect of ionizing radiation on various substances of living and inanimate nature led to the emergence of dosimetry.

Dosimetry - a section of nuclear physics and measurement technology that studies quantities characterizing the effect of ionizing radiation on substances, as well as methods and instruments for measuring them.

The processes of interaction of radiation with tissues occur differently for different types of radiation and depend on the type of tissue. But in all cases, the radiation energy is converted into other types of energy. As a result, part of the radiation energy is absorbed by the substance. Absorbed Energy- the root cause of all subsequent processes that ultimately lead to biological changes in a living organism. The effect of ionizing radiation (regardless of its nature) is assessed quantitatively by the energy transferred to the substance. For this purpose, a special value is used - radiation dose(dose - portion).

Absorbed dose

Absorbed dose(D) - value equal to the energy ratioΔ Ε transferred to the element of the irradiated substance to the massΔ m of this element:

The SI unit of absorbed dose is gray (Gr), in honor of the English physicist and radiobiologist Louis Harold Gray.

1 Gy - This is the absorbed dose of ionizing radiation of any kind, at which 1 J of radiation energy is absorbed in 1 kg of mass of a substance.

In practical dosimetry, a non-systemic unit of absorbed dose is usually used - glad(1 glad= 10 -2 Gr).

Equivalent dose

Magnitude absorbed dose takes into account only the energy transferred to the irradiated object, but does not take into account the “quality of radiation”. Concept radiation quality characterizes the ability of a given type of radiation to produce various radiation effects. To assess the quality of radiation, enter the parameter - quality factor. It is a regulated quantity, its values ​​are determined by special commissions and included in international standards designed to control radiation hazards.

Quality factor(K) shows how many times the biological effect of a given type of radiation is greater than the effect of photon radiation, with the same absorbed dose.

Quality factor- dimensionless quantity. Its values ​​for some types of radiation are given in table. 34.1.

Table 34.1. Quality factor values

Equivalent dose(H) is equal to the absorbed dose multiplied by the quality factor for a given type of radiation:

In SI, the unit of equivalent dose is called sievert (Sv) - in honor of the Swedish specialist in the field of dosimetry and radiation safety Rolf Maximilian Sievert. Along with sievert a non-systemic unit of equivalent dose is also used - rem(biological equivalent of x-ray): 1 rem= 10 -2 Sv.

If the body is exposed several types of radiation, then their equivalent doses (H i) are summed up:

Effective dose

With a single general irradiation of the body, different organs and tissues have different sensitivity to the effects of radiation. So, with the same equivalent dose The risk of genetic damage is most likely when the reproductive organs are irradiated. The risk of lung cancer when exposed to radon α-radiation under equal irradiation conditions is higher than the risk of skin cancer, etc. Therefore, it is clear that radiation doses to individual elements of living systems should be calculated taking into account their radiosensitivity. For this purpose, the weighting coefficients b T (T is the index of the organ or tissue) given in table are used. 34.2.

Table 34.2. Values ​​of weight coefficients of organs and tissues when calculating the effective dose

End of table. 34.2

Effective dose(H eff) is a value used as a measure of the risk of long-term consequences of irradiation of the entire human body, taking into account the radiosensitivity of its individual organs and tissues.

Effective dose is equal to the sum of the products of equivalent doses in organs and tissues by their corresponding weighting coefficients:

Summation is carried out over all tissues listed in table. 34.2. Effective doses, like equivalent doses, are measured in rem And sieverts

Exposure dose

The absorbed and associated equivalent radiation doses are characterized by energetic effect radioactive radiation. As a characteristic ionizing action radiation use another quantity called exposure dose. Exposure dose is a measure of the ionization of air by X-rays and γ-rays.

Exposure dose(X) is equal to the charge of all positive ions formed under the influence of radiation per unit mass of air under normal conditions.

The SI unit of exposure dose is pendant per kilogram (C/kg). Pendant - This is a very large charge. Therefore, in practice they use a non-systemic unit of exposure dose, which is called x-ray(P), 1 R= 2.58x10 -4 Kl/kg. At exposure dose 1 R as a result of ionization in 1 cm 3 of dry air under normal conditions, 2.08 x 10 9 pairs of ions are formed.

The relationship between absorbed and exposure doses is expressed by the relation

where f is a certain conversion factor depending on the irradiated substance and the radiation wavelength. In addition, the value of f depends on the dose units used. f values ​​for units glad And x-ray are given in table. 34.3.

Table 34.3. Conversion factor values ​​from x-ray V glad

In soft tissues f ≈ 1, therefore the absorbed dose of radiation in glad numerically equal to the corresponding exposure dose in X-rays This makes it convenient to use non-system units glad And R.

Relationships between different doses are expressed by the following formulas:

Dose rate

Dose rate(N) is a value that determines the dose received by an object per unit of time.

With uniform radiation action dose rate is equal to the ratio of the dose to the time t during which the ionizing radiation was in effect:

where κ γ is the gamma constant characteristic of a given radioactive drug.

In table Figure 34.4 shows the relationships between dose units.

Table 34.4. Relationships between dose units

34.2. Biological effects of radiation doses. Limit doses

The biological effects of radiation with different equivalent doses are indicated in Table. 34.5.

Table 34.5. Biological effect of single effective doses

Limit doses

Radiation safety standards are established dose limits(PD) irradiation, compliance with which ensures the absence of clinically detectable biological effects of irradiation.

Limit dose- annual value effective doses of man-made radiation that should not be exceeded under normal operating conditions.

The maximum dose values ​​are different for personnel And population. Personnel are persons working with man-made sources of radiation (group A) and who, due to working conditions, are in the sphere of their influence (group B). For group B, all dose limits are set four times lower than for group A.

For the population, dose limits are 10-20 times less than for group A. PD values ​​are given in table. 34.6.

Table 34.6. Basic dose limits

Natural (natural) radiation background created by natural radioactive sources: cosmic rays (0.25 mSv/year); radioactivity of the subsoil (0.52 mSv/year); radioactivity of food (0.2 mSv/year).

Effective dose up to 2 mSv/year(10-20 μR/h), received at the expense natural radiation background, considered normal. As with man-made irradiation, an irradiation level of more than 5 is considered high. mSv/year.

There are places on the globe where the natural background is 13 mSv/year.

34.3. Dosimetric devices. Ionizing radiation detectors

Dosimeters- measuring devices doses ionizing radiation or dose-related quantities. The dosimeter contains detector radiation and a measuring device that is calibrated in units of dose or power.

Detectors- devices that record various types of ionizing radiation. The operation of detectors is based on the use of those processes that cause registered particles in them. There are 3 groups of detectors:

1) integrated detectors,

2) counters,

3) track detectors.

Integrated detectors

These devices provide information about the total flow of ionizing radiation.

1. Photodosimeter. The simplest integrated detector is a light-proof cassette with X-ray film. A photodosimeter is an individual integrated meter that is provided to persons in contact with radiation. The film develops after a certain period of time. By the degree of its blackening, the radiation dose can be determined. Detectors of this type allow you to measure doses from 0.1 to 15 R.

2. Ionization chamber. This is a device for recording ionizing particles by measuring the amount of ionization (number of ion pairs) produced by these particles in a gas. The simplest ionization chamber consists of two electrodes placed in a gas-filled volume (Fig. 34.1).

A constant voltage is applied to the electrodes. Particles falling into the space between the electrodes ionize the gas, and a current arises in the circuit. The current strength is proportional to the number of ions formed, i.e. exposure dose rate. The electronic integrating device also determines the dose of X.

Rice. 34.1. Ionization chamber

Counters

These devices are designed to count the number of ionizing radiation particles passing through working volume or falling on work surface.

1. Figure 34.2 shows a diagram of a gas discharge Geiger-Muller counter, the operating principle of which is based on the formation of an electric pulse discharge in a gas-filled chamber when a separate ionizing particle enters.

Rice. 34.2. Geiger-Muller counter circuit

The counter is a glass tube with a layer of metal (cathode) deposited on its side surface. A thin wire (anode) is passed inside the tube. The gas pressure inside the tube is 100-200 mmHg. A high voltage of the order of hundreds of volts is created between the cathode and anode. When an ionizing particle enters the counter, free electrons are formed in the gas and move towards the anode. Near the thin anode filament, the field strength is high. Electrons near the filament are accelerated so much that they begin to ionize the gas. As a result, a discharge occurs and current flows through the circuit. The self-discharge must be extinguished, otherwise the counter will not react to the next particle. A significant voltage drop occurs across the high-resistance resistance R connected to the circuit. The voltage on the meter decreases and the discharge stops. Also, a substance is introduced into the gas composition, which corresponds to the fastest quenching of the discharge.

2. An improved version of the Geiger-Muller counter is proportional counter, in which the amplitude of the current pulse is proportional to the energy released in its volume by the detected particle. This counter determines absorbed dose radiation.

3. The action is based on another physical principle scintillation counters. Under the influence of ionizing radiation, scintillations occur in some substances, i.e. flashes, the number of which is counted using a photomultiplier tube.

Track detectors

Detectors of this type are used in scientific research. IN track detectors the passage of a charged particle is recorded in the form of a spatial picture of the trace (track) of this particle; the painting may be photographed or recorded by electronic devices.

A common type of track detector is Wilson chamber. The observed particle passes through a volume filled with oversaturated steam, and ionizes its molecules. Vapor condensation begins on the formed ions, as a result of which the trace of the particle becomes visible. The camera is placed in a magnetic field, which bends the trajectories of charged particles. The curvature of the track can be used to determine the mass of the particle.

34.4. Methods of protection against ionizing radiation

Protection from the negative effects of radiation and some ways to reduce radiation dose are listed below. There are three types of protection: protection by time, distance and material.

Protection by time and distance

For a point source, the exposure dose is determined by the relation

from which it is clear that it is directly proportional to time and inversely proportional to the square of the distance to the source.

A natural conclusion follows from this: to reduce the damaging effects of radiation, it is necessary to stay as far as possible from the source of radiation and, if possible, for as little time as possible.

Material protection

If the distance to the radiation source and the exposure time cannot be maintained within safe limits, then it is necessary to protect the body with material. This method of protection is based on the fact that different substances absorb all kinds of ionizing radiation falling on them in different ways. Depending on the type of radiation, protective screens made of various materials are used:

alpha particles- paper, a layer of air several centimeters thick;

beta particles- glass several centimeters thick, aluminum plates;

X-ray and gamma radiation- concrete 1.5-2 m thick, lead (these radiations are attenuated in the substance according to an exponential law; a larger thickness of the shielding layer is needed; in X-ray rooms a leaded rubber apron is often used);

neutron flux- slows down in hydrogen-containing substances, such as water.

For individual respiratory protection from radioactive dust, respirators.

In emergency situations related to nuclear disasters, you can take advantage of the protective properties of residential buildings. Thus, in the basements of wooden houses, the dose of external radiation is reduced by 2-7 times, and in the basements of stone houses - by 40-100 times (Fig. 34.3).

In case of radioactive contamination of the area, it is controlled activity one square kilometer, and if food is contaminated - their specific activity. As an example, we can point out that when an area is contaminated by more than 40 Ci/km 2, the inhabitants are completely evicted. Milk with a specific activity of 2x10 11 Ci/l or more cannot be consumed.

Rice. 34.3. Shielding properties of stone and wooden houses for external γ-radiation

34.5. Basic concepts and formulas

Table continuation

End of table

34.6. Tasks

1. A study of radiation cataracts on rabbits showed that under the influence γ - radiation cataracts develop at a dose of D 1 = 200 rad. Under the influence of fast neutrons (accelerator halls), cataracts occur at a dose of D 2 = 20 rad. Determine the quality factor for fast neutrons.

2. By how many degrees will the temperature of a phantom (model of a human body) weighing 70 kg increase at a dose of γ-radiation X = 600 R? Specific heat of the phantom c = 4.2x10 3 J/kg. Assume that all the energy received is used for heating.

3. A person weighing 60 kg was exposed to γ-radiation for 6 hours, the power of which was 30 μR/hour. Assuming that the main absorbing element is soft tissue, find the exposure, absorbed and equivalent radiation doses. Find the absorbed radiation energy in SI units.

4. It is known that a single lethal exposure dose for humans is 400 R(50% mortality). Express this dose in all other units.

5. In tissue weighing m = 10 g, 10 9 α-particles with energy E = 5 MeV are absorbed. Find the equivalent dose. The quality factor for α-particles is K = 20.

6. Exposure dose rate γ -radiation at a distance r = 0.1 m from a point source is N r = 3 R/hour. Determine the minimum distance from the source at which you can work daily for 6 hours without protection. PD = 20 mSv/year. Absorption γ - do not take into account radiation from air.

Solution(careful alignment of units of measurement required) According to radiation safety standards equivalent dose, received over a year of work is H = 20 mSv. Quality factor for γ -radiation K = 1.

Applications

Fundamental physical constants

Factors and prefixes for the formation of decimal multiples and submultiples and their designations

A prerequisite for radiation safety during radiation therapy is an accurate quantitative accounting of the radiation energy absorbed by personnel and patients exposed to radiation.

To quantitatively characterize AI, the concept of “dose” is used. The radiation dose is the ratio of radiation energy to the mass or volume of the irradiated substance. In clinical dosimetry the following concepts are used:

Activity of a radioactive substance - characteristic of the amount of radioactive substance (number of decays per unit time). The system unit of activity is Becquerel (Bq)- activity of a radioactive source in which 1 decay occurs in 1 second (1 Bq = 1 decay/s). Non-systemic unit - Curie (Ci)- activity of a radioactive source in which 3.7  10 10 decays occur in 1 second.

Table 1

Basic radiation quantities and their units

 Since 1 Gy is, by definition, 1 Joule per kilogram, the SI unit of integral dose greykilogram is converted to Joule

(1 Gykg = 1 (J/kg)kg = 1 J).

Exposure dose of radiation - radiation dose, which is measured in dry (free) air in the absence of scattering bodies. It mainly characterizes source radiation (its power, constancy of parameters, etc.). The exposure dose is applied only to ionizing radiation with an energy of no more than 3 MeV.

The non-systemic unit of exposure dose is X-ray is the dose of x-ray or-radiation, which under normal conditions (0 0 C and pressure 1 atmosphere) per 1 cm 3 air forms a charge equal to 1 oe. With. e. static electricity (2.08 x 10 9 pairs of ions of each sign).

The SI unit for measuring exposure dose is pendant per kg is the dose of x-ray or- radiation, in which a charge equal to 1 coulomb is formed in 1 kg of air under normal conditions.

The same dose can be given at different intervals. Therefore, the concept is introduced power dose - dose calculated per unit of time. The biological effect of ionizing radiation depends on both the dose and its power.

Absorbed radiation dose - the main quantitative indicator of the impact of ionizing radiation on irradiated tissue. It is determined by the amount of energy transferred during the irradiation process to a unit mass of the irradiated substance. The absorbed dose applies to any type of ionizing radiation. The SI unit of absorbed dose is J/kg. This quantity is called " Gray" (Gr). This is the dose of ionizing radiation at which 1 kg of irradiated substance absorbs energy equal to 1 J. Extrasystemic unit of absorbed dose - glad. 1 rad - This is the dose of radiation at which 1 g of irradiated substance absorbs energy equal to 100 ergs.

Integral radiation dose - the amount of energy absorbed in the irradiated volume.

Due to the fact that when biological objects are irradiated, different types of ionizing radiation at the same absorbed dose have different biological effects, there is the concept of “equivalent radiation dose”. The biological effects caused by a particular type of radiation are compared to the effect produced by photon radiation with an energy of 200 keV.

A coefficient showing how many times the radiation hazard in the case of chronic human irradiation (in small doses) for a given type of radiation is higher than in the case of photon radiation (200 keV at an equal absorbed dose) is called the quality factor (QC). CC for photon radiation 200 keV = 1. For α-particles CC = 20, for protons and fast neutrons CC = 10, for thermal neutrons CC = 2.5-3. The value of CC depends on the LET of a given type of radiation. The higher the LET, the greater the cell damage and the lower the ability to recover. Thus, with the same absorbed dose, the damaging (or healing) effect of proton irradiation will be 10 times greater than that of photon radiation.

The dose received by a living object, taking into account the QC of a given radiation, is called equivalent dose . The equivalent dose takes into account the absorbed dose and the biological effect of the AI. The concept of "equivalent dose" is used only for assessing radiation hazard. The non-systemic unit of equivalent dose is RER - this is a dose of some type of AI, biologically effective 1 Roentgen of x-ray radiation generated by a voltage of 200 kV.

Currently, it is recommended in all cases to use physical quantities expressed in SI units. However, in medical radiotherapy technology, non-system units have been used for a long time, which is widely reflected in the relevant literature, instructions, and instrument scales (including dosimeters). Therefore, it is necessary to know the relationships between non-systemic units and SI units (Table 1).

Methods for dosimetry of ionizing radiation

AIs do not have smell, taste, or any other properties that would allow a human to register them. To measure the quantitative and qualitative characteristics of radiation, various methods are used, based on recording the effects of interaction of radiation with matter.

Dosimeters are instruments designed to measure the dose or dose rate of AI. These devices are based on the registration and quantitative assessment of ionization, scintillation, photographic, chemical and other effects that arise during the interaction of artificial intelligence with matter.

Main groups of dosimeters:

Clinical - for measuring IS in the working beam.

Used in preparation for radiation therapy and during irradiation.

Protection monitoring dosimeters - for measuring the dose rate of scattered radiation at workplaces (in the radiation safety system). These dosimeters must be direct reading.

Individual - to control the exposure of persons working in the area of ​​influence of AI.

Dosimetry methods:

Biological - based on the assessment of reactions that occur in tissues when irradiated with a certain dose of radiation (erythemal dose, epilation dose, lethal dose).

They are indicative and are used mainly in experimental radiobiology. Chemical - involve recording irreversible chemical reactions occurring in certain substances under the influence of irradiation (radiochemical method, photographic method).

Radiochemical method- is based on the oxidation reaction of divalent iron into ferric iron under the influence of II (Fe 2+ Fe 3+), which leads to a change in color (transparency). Ferrosulfate dosimeters are used. Since the range of these dosimeters is very large (from 20 to 400 Gy), they are used only for emergency situations.

Photographic method

Scintillation dosimeters. Thallium activated sodium iodide crystals are used. When the AI ​​hits them, light flashes appear, which are converted into electrical impulses, amplified and recorded by counting devices. Scintillation dosimeters are not used in clinical dosimetry due to their large volume and high sensitivity, which makes it possible to recommend their use in protection dosimetry.

Thermoluminescent dosimeters (TLD). Some solid crystalline substances are capable of luminescing under the influence of radiation. The dose is determined by the intensity of the glow. TLDs are small in volume and are indirectly indicating (the dose accumulates over some time). Widely used in clinical dosimetry (measurement of dose on a patient, in the body cavity) and as individual dosimeters.

Ionization chamber- this is a capacitor. It consists of two electrodes, the space between which is filled with air. Under the influence of AI, the air is ionized, creating an electric current. We judge the dose by the magnitude of the current. Dosimeters based on the ionization method are currently the most common. Widely used in clinical dosimetry, protection dosimetry and personal dosimetry.

Gas discharge meter. The ionization effect of radiation is also used. But a much higher voltage is applied to the electrodes of the gas-discharge meter. Therefore, the electrons produced in the counter during irradiation acquire greater energy and themselves cause mass ionization of atoms and gas molecules. This allows very small doses of radiation to be recorded using gas-discharge counters.

Semiconductor (crystalline) dosimeters. Conductivity changes depending on the dose rate. Widely used along with ionization dosimeters.

DOSIMETRY OF IONIZING RADIATION(Greek dosis dose, portion + metreo measure) - a branch of radiation physics and measurement technology dealing with the measurement and study of ionizing radiation fields (photon and corpuscular), the study of the effects of their interaction with matter, as well as the dose fields created as a result (see. ) in matter. D. and. And. widely used in the development of methods for generating radiation fields and dose fields with specified parameters. Means D. and. And. used in the development and use of sources of ionizing radiation in the national economy, science and medicine.

The emergence and development of D. and. And. associated with the discovery and practical use of X-ray and gamma radiation, neutrons and other nuclear particles, with the study of their biol, action. It has become necessary to dose beneficial radiation effects when exposed to radiation on various materials and biological tissues, to control radiation safety conditions for the entire population, especially for people working in the area of ​​radiation (see Dosimetric control). D. and. And. made a great contribution to solving the problems of radiation safety of space flights.

For medicine D. and. And. is one of the related physical disciplines. She is engaged in the development of scientific foundations, methods and solving applied problems of radiation therapy, radiation hygiene and other areas of medicine. radiology.

In the 60-70s. 20th century a wedge has developed, dosimetry, edges is an integral part of radiation therapy. Dosimetry has acquired independent significance in radiation hygiene. There are real prerequisites for the formation of radiobiol. dosimetry, edges must take into account the special conditions for the implementation of radiation processes in biol, objects at the cellular and molecular levels.

D. and. And. has many computational and experimental methods. Calculation methods are based on the physics of the interaction of ionizing radiation with matter and use modern means of electronic computing technology, experimental methods, and experimental methods. And. are based on the use of specially selected substances to measure dosimetric quantities of various macroscopic effects of irradiation.

The main one in dosimetry is the ionization measurement method. It is associated with the main property of ionizing radiation - the ability to ionize matter. Other methods are based on the conversion of the energy of ionizing radiation into visible light (luminescent method), on changes in the properties of semiconductors under the influence of radiation (semiconductor method), on the radiolysis of substances as a result of chemical reactions. reactions (chemical method), on the blackening of the photographic emulsion or the appearance of images of traces of ionizing particles in it (photographic method), on the direct measurement of the heat released in the substance (calorimetric method). Finally, in D. and. And. Radiation effects observed on the chromosome set of cells can be used (biol, method).

Any method of D. and. And. is a physical measurement. As a result of its application, the numerical value of one or another physical is obtained. magnitude (dosimetric characteristics). This also applies to the biol method, in which it is not the biol effect itself that is measured, but its certain physical properties. measure, and it is called biological only because the direct detector of radiation is a biological object, or because the measured value is associated with a certain biological characteristic. Mixing physical and biol, concepts can lead to a misconception about the so-called. biological dose, which is often used in radiobiol. and other studies.

Based on the registration of radiation using one or another dosimetry method, it is possible to obtain information not only about radiation fields and dose fields, but also about radiation sources, their isotopic composition and distribution in space, in the irradiated body. This aspect is important for solving many problems of radiation hygiene (see), radioisotope diagnostics, experimental biology and medicine, which widely use the method of radioactive tracers in their research. As a rule, here we have to deal with radiation sources of relatively low activity and, accordingly, with extremely low radiation doses. In fact, we are talking about recording photon and particle fluxes, analyzing their energy spectra, and studying their time characteristics. Measuring them has its own specifics and requires special techniques, instruments and information processing tools. This is dealt with by a special section of radiation measuring technology - radiometry (see). However, between D. and. And. and radiometry there are no sharp differences and no clear division of functions. Their methods and means have much in common and in many cases complement each other.

Dosimetry of each type of ionizing radiation has its own methodological, metrol. and other features.

The dosimetry of X-ray and gamma radiation with energies up to 3 MeV has been most fully developed, with the exception of the low-energy region (up to several tens of keV), where dose characteristics depend on the energy spectrum of the radiation, which varies significantly depending on the depth in the substance and irradiation conditions. Particularly highlighted is the dosimetry of neutrons, which do not directly produce ionization, but create it indirectly, through secondary heavy charged particles (protons, deuterons, alpha particles, etc.). Secondary heavy charged particles, interacting with tissues, form tracks (traces of particle movement) with a high linear ionization density (LID), i.e., with a high linear energy transfer (LET) of radiation to tissue microstructures (see Linear energy transfers). The latter sometimes contributes to more intensive development of radiobiol. effects and ultimately leads to increased biol, an action equivalent to the absorption of more radiation energy (with low LET) than that which was actually absorbed in the tissues (with high LET). Therefore, they say that neutrons and other densely ionizing radiation have a high relative biol. efficiency - RBE (see Relative biological effectiveness of radiation); Conventionally, consider RBE = 1 for X-ray radiation with a generation energy of approx. 200 kV.

Since the 60s 20th century A special section of D. and. is intensively developing. i., called microdosimetry. Microdosimetry studies the microscopic distribution of energy during the interaction of radiation with matter (photons and particles with nuclei, atoms of matter, with cellular structures and tissue cells). The statistical nature of this interaction is taken into account for a deeper understanding of radiobiol. processes at the cellular and molecular levels and the role of the distribution of absorbed radiation energy across the LET. This is especially important for mixed radiation dosimetry, for the optimal use of different types of radiation in medical care. radiology.

The main concept of D. and. And. is the absorbed dose of radiation - a measure of the energy density transferred by radiation to a substance. Other physical values ​​of more narrow application are: exposure dose of radiation for X-ray and gamma radiation with photon energy up to 3 MeV; equivalent radiation dose - in radiation safety tasks (see Doses of ionizing radiation).

These physical quantities and units of measurement were developed within the framework of the International Commission on Radiation Units and Measurements (ICRU).

Clinical dosimetry of ionizing radiation

The use of ionizing radiation for the diagnosis and treatment of cancer and other patients requires a correct quantitative and qualitative assessment of the nature of the distribution of radiation energy in the irradiated environment.

The main task of wedge, dosimetry in radiation therapy (see) is the selection and justification of methods and means of irradiation that ensure the most favorable distribution of the absorbed dose of radiation in the body for a given patient. When treating oncology patients, this task comes down to creating such a dose field (see), in which patol, the focus and possible routes of metastasis will receive the necessary and sufficient dose of radiation, causing destruction of tumor tissue, with the least energy absorption by normal tissues and especially vital important organs. The energy of ionizing radiation must be fractionated in time so as to provide the greatest therapeutic effect.

In radiation diagnostics, optimization of irradiation conditions comes down to the choice of irradiation conditions and methods under which the most complete diagnostic information can be obtained with the least radiation exposure to the body.

Wedge, dosimetry uses computational and experimental methods. Calculation methods are based on physical laws of interaction of ionizing radiation with matter. They are used to determine the radiation dose in air in order to characterize the radiation field of sources of various configurations and to determine the absorbed dose in the irradiated body.

Experimental methods of wedge and dosimetry are aimed at obtaining data on the spatial distribution of the absorbed radiation dose in the irradiated body. For this purpose, various model systems are used - phantoms made of tissue-equivalent materials (see Dosimetric phantom), inside which the radiation dose distribution is measured.

The initial data for radiotherapy are the characteristics of radiation beams in air. By systematic dosimetric monitoring (see), the exposure dose rate is established at given focal lengths and at certain irradiation fields. The qualitative composition of the radiation is determined by the effective photon energy or the layer of half-attenuation of the dose rate. Based on the data obtained, using tables of relative depth doses or isodose graphs, taking into account the irradiation conditions for a given patient, the exposure dose is determined for a homogeneous tissue-equivalent medium simulating the irradiated body. Knowing the qualitative composition of the radiation and the properties of the tissues through which the beam of rays passes, the exposure dose is converted into absorbed dose and, thus, data is obtained on the spatial distribution of the absorbed dose. Taking into account the heterogeneity of human tissues, an appropriate correction is introduced into the dose distribution. If the isodose maps do not contain the irradiation conditions necessary for a given patient, or for the purpose of clarification, phantom measurements are made on a specially made phantom that reproduces the irradiated organ or part of the body in shape, size and composition.

For multifield and moving irradiation, dose fields are summed up. To form a dose field, various devices are used - lattice and wedge-shaped filters, protective blocks, etc. Dose fields are compiled taking into account the individual characteristics of the patient. When choosing the optimal radiation therapy plan for a given patient, it is necessary to have several conditional sections passing through the center of the pathol, focus in the horizontal, frontal and sagittal directions. Conditional sections are made on transparent paper or film according to X-ray data, examination, measurement of the patient’s external contour and an atlas of anatomical sections. The conventional section indicates the location of the patol, lesion and vital organs. The slice is applied to dose maps in accordance with various dose distribution options and the optimal irradiation option is selected.

To summarize dose fields and select optimal irradiation conditions in the practice of radiation therapy, universal electronic, digital (ECVM) and analog-digital (ADVM) computers are widely used. The calculation results are output to a digital printing device, which records the resulting dose distribution, taking into account the individual characteristics of the patient (cut contour and tissue heterogeneity).

When solving wedge problems, dosimetry, more and more attention is paid not only to spatial, but also to temporal optimization, i.e., delivering not only the necessary and sufficient dose to the focus, but also the optimal fractionation of the absorbed dose. A system for spatiotemporal optimization of irradiation conditions and methods is being developed. These problems are also solved on a computer using dynamic programming methods.

Ionizing radiation dosimeters

Ionizing radiation dosimeters are instruments that measure the dose or dose rate of radiation. Dosimeters differ in both their functional purpose and operating principle.

By purpose, dosimeters are divided into:

1) dosimeters for monitoring radiation-chemical processes with a measurement range of 10 4 - 10 10 R;

2) dosimeters for wedge, and radio-biol. measurements with a measuring range of 1×10 4 P or 0.1×10 3 P/min;

3) personal radiation monitoring devices with a measurement range of 0.01 - 100 P;

4) instruments for monitoring radiation safety (with a dose rate measurement range of 0.1×10 3 μR/sec); These usually also include radiometers - instruments for measuring ionizing radiation, determining the flux density of ionizing radiation (see Radioisotope diagnostic instruments).

Based on the type of radiation recorded, a distinction is made between dosimeters of X-ray and gamma radiation, beta dosimeters, neutron dosimeters and dosimeters for measuring mixed radiation (for example, gamma and n; beta and gamma). The main parameters of dosimeters include: accuracy class, measurement range, stability of readings over time, change in sensitivity over the energy range.

The dosimeter consists of two main functional units - a detection unit (detector) and an electronic measuring device. A detection unit is a device designed to convert the energy of ionizing radiation into another type of energy convenient for measurement. According to physical The process occurring in detectors under the influence of ionizing radiation is distinguished between ionization, luminescence (usually scintillation is distinguished separately), chemical, photographic, calorimetric, semiconductor dosimeters, as well as dosimeters with combined detectors (for example, semiconductor + scintillator).

Ionization dosimeters are based on the use of an electric field to collect ions formed by ionizing radiation in a substance; they are most widely used. In its simplest form, an ionization detector consists of two parallel plates, between which a voltage is applied. The conductivity of the gas between the plates depends on the applied voltage. Types of detectors are characterized by the portion of the current-voltage characteristic for which it operates.

In everyday practice, the so-called thimble ionization chambers, the operation of which is based on the Bragg-Gray principle - measuring the ionization of gas in a microcavity inside a solid substance, the thickness of the walls is greater than the range of secondary electrons. In this case, the ionization of the gas is caused by electrons released in the solid. Thus, by measuring the ionization of the gas in the cavity, it is possible to determine the dose rate or dose in the wall material. If the wall material has the same effective atomic number as air (tissue), then the exposure dose of photon radiation in roentgens (absorbed dose in rads) is determined. Air- or tissue-equivalence of the material of the chamber walls, the edges of which determines the dependence of the readings on the radiation energy (“strength movement” of the dosimeter), is one of the important requirements, especially for wedges, dosimetry.

Examples of ionization dosimeters of X-ray and gamma radiation are dosimeters of the DIM-60 type (Fig. 1), dosimeter DRG 2-01 "Vitim", dosimeter DRG 2-03 (Fig. 2 and 3), dosimeter I DM D-1 "Krug" ", a set of individual dosimeters KID-20 and KID-60.

Wedge, dosimeter (dose and dose rate meter) IDMD-1 “Circle” is designed to measure the exposure dose of X-ray and gamma radiation. The detector is made in the form of a probe, allowing for intracavitary and phantom measurements. The volume of the ionization chamber is 0.2 cm 3 .

Dosimeters KID-20 and KID-60 with capacitor ionization chambers in the shape of a pen are designed for individual monitoring and provide control of the dose of X-ray and gamma radiation in the range from 0.01 to 50 R.

Ionization dosimeters are used not only for X-ray and gamma radiation dosimetry. Dosimeters have been developed for measuring bremsstrahlung and high-energy electron radiation, for example, an electrometer - a meter of absorbed energy and parameters of a beam of gamma and electron radiation DKS2-01 "Vetluga", a dosimeter DBM-1 (Fig. 4), etc.

Other ionization dosimeters (and radiometers) are based on the use of gas-discharge counters as a detector, in which an electrical pulse occurs when charged particles of ionizing radiation pass through it. These devices have a higher sensitivity to radiation than ionization chambers, so they are used when measuring low dose rates. Gas-discharge counters have found wide application in stationary and portable devices for monitoring the radiation situation.

An example is the recording dosimeter DRG-3-2eM (Fig. 5).

Luminescent dosimeters are based on radiophotoluminescence or radiothermoluminescence, which consists in the fact that charge carriers formed in a phosphor detector under the influence of ionizing radiation are localized in capture centers. Due to this, the absorbed energy accumulates; the edges can be released in the form of luminescence with additional excitation. Additional excitation can be caused either by illumination of the phosphor-detector with a certain part of the spectrum (usually ultraviolet light) - radiophotoluminescence, or by heating - radiothermoluminescence. Silver-activated aluminophosphate glasses are used as detectors for radiophotoluminescent dosimeters, and manganese-activated aluminophosphate glasses, lithium fluoride, calcium fluoride, lithium metaborate, etc. are used as thermoluminescent detectors. A distinctive feature of luminescent dosimeters is that the detectors are not connected to an electronic device, and their small size, and an additional advantage is the possibility of long-term storage (up to several months) of dosimetric information and summation of doses during multiple irradiations, which is essential when determining the total dose to a tumor during a course of radiation therapy. In dosimetric practice, thermoluminescent dosimeters IKS-A, DTM-2 (Fig. 6), TELDE (Fig. 7), TDP-2 and photoluminescent dosimeter DFM-1 are used.

Scintillation dosimeters, the detection unit of which consists of a scintillator and a photomultiplier, are highly sensitive. Ionizing radiation, interacting with the scintillator substance, forms electrons in it, which, when absorbed in the scintillator, create flashes of light. A photomultiplier converts light into an electric current proportional to the dose rate.

Chemical dosimeters are based on the determination of chemical. changes that occur in some substances under the influence of ionizing radiation. For chem. dosage

metry uses aqueous solutions of iron sulfate (ferrosulfate method), cerium sulfate (cerium method), benzene, methylene blue, organic halogen compounds, etc. A significant advantage of the chemical. dosimeters is the tissue equivalence of a number of chemicals. systems used as detectors.

Chem. A dosimeter using ferrosulfate solution has found wide application in metrology.

Photographic dosimeters (PDOs) have become widespread in individual dosimetry. X-ray film is used as a detector (Fig. 10). The photographic dosimetry method is based on the property of ionizing radiation to affect the sensitive layer of photographic materials in a similar way to visible light. This method can be used to record dose in mixed radiation fields, including gamma and beta radiation. The advantage of the method is its documentation, the disadvantage is a large measurement error, a significant “movement with rigidity”; in addition, even photographic films from the same batch have different sensitivity to radiation.

Calorimetric dosimeters are based on measuring the amount of heat released when radiation is absorbed. The calorimetric method is one of the main absolute measurement methods, with the help of which the unit of absorbed dose of ionizing radiation is reproduced. However, this method is too technically complex to be recommended for routine measurements.

Dosimeters with semiconductor detectors. In such detectors, under the influence of ionizing radiation, the conductivity changes, so that the current depends on the dose rate. The sensitivity of semiconductor detectors to ionizing radiation is much higher than the sensitivity of ionization chambers. This makes it possible to significantly reduce the size of the semiconductor detector, which is very important for wedge dosimetry.

All semiconductor detectors can be divided into three main groups: surface barrier, diffusion and lithium drift. They differ from each other mainly only in the type of part of the detector that is sensitive to ionizing radiation. In dosimetry, semiconductors based on germanium, silicon, gallium arsenide, cadmium sulfide, etc. are used. For example, the “Silicon-1” dosimeter uses a silicon semiconductor detector.

Dosimeters with combined detectors are a combination of a semiconductor and a scintillator, which can significantly increase sensitivity to ionizing radiation. The combination of semiconductor detectors with different effective atomic numbers (the same combination of thermoluminescent and other detectors) makes it possible to determine the quality of radiation from the difference in detector signals. This method makes it possible to widely introduce non-tissue-equivalent detectors into wedge practice.

An isodosegraph is a dosimeter that can be used to automatically obtain pictures of the dose distribution in the irradiated object. It is a device consisting of a detector, a measuring device, a recording device and a mechanism for moving the detector in a tissue-equivalent phantom. There are two types of isodosegraphs: in some, the detector moves along a line of equal doses (isodose); in others, the movement is carried out according to a given program (usually a rectangular raster). In both cases, the dose distribution pattern is obtained in the form of a family of isodose lines. A modern isodosegraph is a complex dosimetric installation consisting of an isodosemeter itself, an intermediate device and a computer. Information obtained from the entire survey field is applied to punched cards, and then a dose field is automatically constructed using a computer.

see also Doses of ionizing radiation.

Bibliography: Ivanov V.I. Dosimetry course, M., 1970, bibliogr.; Isaev B.M. and Bregadze Yu. I. Neutrons in a radiobiological experiment, M., 1967, bibliogr.; Clinical dosimetry, Recommendations of the International Commission on Radiological Units and Measurements, Ser. tech. report No. 43, Vienna, IAEA, 1965; KrongauzA. N., Lyapidevsky V.K. and Frolova A.V. Physical foundations of clinical dosimetry, M., 1969, bibliogr.; Moiseev A. A. and Ivanov V. I. Handbook of dosimetry and radiation hygiene, M., 1974; Radiation dosimetry, ed. J. Hine and G. Brownell, trans. from English, M., 1958, bibliogr.; Radiation Medicine, ed. A. I. Bur-nazyan, p. 5, M., 1968, bibliogr.; T Yu-biana M. et al. Physical foundations of radiation therapy and radiobiology, trans. from French, M., 1969.

M. Sh. Weinberg; A. N. Krongauz (class), V. A Volkov, Lee Dong Hwa (tech.).

Dosimetry of ionizing radiation

a section of applied nuclear physics that examines the properties of ionizing radiation, physical quantities characterizing the radiation field and the interaction of radiation with matter (dosimetric quantities). In a narrower sense of the word D. and. And. - a set of methods for measuring these quantities. The most important feature of dosimetric quantities is their connection with radiation-induced effects that occur during irradiation of living and inanimate objects. Radiation-induced effects in a general sense mean any changes in the irradiated object caused by exposure to ionizing radiation (Ionizing radiation). The main dosimetric quantity is the Dose of ionizing radiation and its modifications. Task D. and. And. - description of the dose field formed in a living organism under real irradiation conditions.

The need to develop D. and. And. arose shortly after the discovery by Roentgen (W.K. Röntgen) in 1895 of the radiation named after him (see X-rays (X-rays)). The intensive accumulation of data on the biological effects of X-ray radiation, on the one hand, opened up a real prospect for its use in medicine, and on the other, pointed to the danger of uncontrolled irradiation of a living organism. As a result, the question arose about dosimetric support for the practical use of ionizing radiation sources. At the beginning of the 20th century. The main sources of radiation were X-ray machines and D. and. And. was actually reduced to dosimetry of photon-ionizing radiation (X-ray and gamma radiation). Then, with the development of technical means of nuclear physics, the creation and improvement of charged particle accelerators, and especially after the launch of the first nuclear reactor in 1942, the number of sources and associated types of ionizing radiation expanded significantly.

The physical basis of D. and. And. is the transformation of radiation energy in the process of its interaction with atoms or their nuclei, electrons and molecules of the irradiated medium, as a result of which part of this energy is absorbed by the substance. Absorbed energy is the root cause of the processes leading to the observed radiation-induced effects, and therefore dosimetric quantities are related to the absorbed radiation energy.

The variety of irradiation conditions and its multifactorial consequences do not allow one to make do with a single dosimetric value, adapting it to changes in these conditions and factors. A whole dosimetric quantity is required, from which, depending on the irradiation conditions and the task at hand, the most adequate measure of the radiation-induced effect is selected. An example of such a value is the equivalent dose indicator introduced by the International Commission on Radiological Units (ICRU) for radiation safety purposes (see Dose of ionizing radiation) at a point in the radiation field - the maximum equivalent dose inside a tissue-equivalent ball with a diameter of 30 cm when the center of this ball coincides with a given point. The practical application of this indicator encounters certain difficulties, because the problem of the adequacy of dosimetry cannot yet be considered completely resolved.

With D. and. And. use both instrumental and computational methods. All dosimetric instruments are designed on the principle of recording radiation-induced effects in a certain model object - an ionizing radiation detector. In the early period of development of D. and. and, photographic effects of ionizing radiation, chemical transformations and heat were used. As methods for recording elementary particles developed, so did the methods of digital imaging. And. In modern conditions, a wide range of radiation-induced effects is used. To those already mentioned can be added ionization effects in gases and condensed media, changes in the electrical properties of semiconductors, destructive solids, luminescence, scintillation, etc.

A special place is occupied by the biological one, which uses quantitative radiobiological effects as a measure of dosimetric magnitude, for example, chromosomal aberrations, changes in the morphological composition of the blood, and other indicators that are uniquely related to D. and. And. (see Radiation sickness, Radiosensitivity).

Methods D. and. And. can be classified according to different criteria. Thus, depending on the type of the recorded effect, ionization, photographic, chemical, luminescent, calorimetric, scintillation methods, the method of damage traces, etc. are distinguished. In this case, there is an unambiguous quantitative relationship between the change in the physical or chemical properties of the radiation detector and the absorbed energy. In clinical dosimetry, ionization methods are common, in which solid-state luminescent crystals and semiconductors serve as detectors. The latter are attracted by the small size of the detector.

In the USSR, stationary, portable and individual dosimetric devices are produced. Stationary dosimeters are used in clinical practice, and wearable ones are most often used to assess the radiation situation for the purposes of radiation protection. They are autonomous and therefore can be used in any environment, incl. in the field. Personal dosimeters are designed to assess the dose received by persons working in contact with ionizing radiation. They can be directly showing ( rice. a, b ) or consist of ionization or thermoluminescent detectors (c) worn by personnel, which, proportional to the radiation dose, are determined on a special reading device.

Clinical dosimetry- section D. and. i., engaged in measurements and calculations of quantities characterizing the physical and biophysical effects of irradiation of patients receiving radiation therapy (Radiation therapy). The main task of clinical dosimetry is to quantitatively describe the spatial and temporal distribution of absorbed radiation energy in an irradiated patient, as well as to search, justify and select individually optimized conditions for his irradiation.

The basic concepts and quantities of clinical dosimetry are absorbed dose (see ionizing radiation (Ionizing radiation dose)), dosimetric phantom, . The dose field is the spatial distribution of the absorbed dose (or its power) in the irradiated part of the patient’s body, a tissue-equivalent environment or a dosimetric phantom that models the patient according to the physical effects of the interaction of radiation with matter, the shape and size of organs and tissues and their anatomical relationships. Information about the dose field is presented in tabular, matrix form, and also in the form of curves connecting points of equal values ​​(absolute or relative) of the absorbed dose. Such curves are called isodoses, and their families are called isodose maps. The absorbed dose at any point in the dose field can be taken as a conventional unit (or 100%), in particular the maximum absorbed dose, which must correspond to the target to be irradiated (i.e., the area covering the clinically identified and expected zone of its distribution).

The formation of the dose field depends on the type and source of radiation, the method of irradiation (external, internal, static, moving, etc.), the patient’s physique, as well as the type of radiation therapeutic device. Therefore, the technical documentation of the device includes an atlas of dose fields and recommendations for its practical use. If necessary (for new options and complex irradiation plans), phantom measurements of dose fields are performed in medical institutions using clinical dosimeters with small-sized ionization chambers or other (semiconductor, thermoluminescent) detectors, dose field analyzers or isodosegraphs. Thermoluminescent detectors are also used to monitor absorbed doses in patients.

The radiation specialist, together with a physicist engineer, conducts dosimetric planning - selects the irradiation method, optimizes the conditions for irradiating the patient by calculating competing options for dose fields, determines the irradiation technology on a specific device, and also monitors the implementation of the adopted plan and its dynamic adjustment in the process of radiation treatment. In connection with the development of methods and means of computer technology, the emergence of high-speed computers with large amounts of memory and means of automated input into the computer of initial graphic and text information about the patient, a gradual transition is taking place from manual to computer planning of radiation exposure. This opens up the possibility of solving the inverse problem of clinical dosimetry - determining the irradiation conditions based on the dose field specified by the doctor.

The USSR Ministry of Health system has a radiation metrological service that checks clinical dosimeters and dosimetric certification of radiation devices. In 1988, the USSR began the transition to metrological support for radiation therapy based on direct measurements of the absorbed dose in water, traceable to the state primary standard of the unit of its power. All this helps to increase the accuracy of planning and implementation of irradiation.

According to modern international requirements, to increase the effectiveness of radiation therapy in clinical dosimetry, it is necessary to strive to dose the patient’s radiation with an error of no more than 5%, based on the absorbed dose in the target, and measurements of absorbed doses should be carried out with an error of no more than 3%.

Bibliography: Ivanov V.I. Dosimetry course, M., 1988; Klepper L.Ya. Formation of dose fields by remote radiation sources, M., 1986, bibliogr.; Krongauz A.N., Lyapidevsky V.K. and Frolova A.V. Physical foundations of clinical dosimetry, M., 1969; Ratner T.G. and Fadeeva M.A. Technical and dosimetric support for remote gamma therapy, M., 1982, bibliogr.

1. Small medical encyclopedia. - M.: Medical encyclopedia. 1991-96 2. First aid. - M.: Great Russian Encyclopedia. 1994 3. Encyclopedic Dictionary of Medical Terms. - M.: Soviet Encyclopedia. - 1982-1984.

See what “Dosimetry of ionizing radiation” is in other dictionaries:

dosimetry of ionizing radiation- radiation dosimetry - [A.S. Goldberg. English-Russian energy dictionary. 2006] Topics energy in general Synonyms radiation dosimetry EN radiation dos ... Technical Translator's Guide

The main methods for recording ionizing radiation: ionization, ions formed by radiation are recorded, scintillation, light flashes arising in a special material are recorded, calorimetric registration... ... Wikipedia

- (from the Greek dosis share, portion, reception and metreo measure), measurement, research and theory. calculations of those characteristics of ionizing radiation (and their interaction with the environment), on which radiation depends. effects in irradiated objects of living and inanimate nature.... ... Physical encyclopedia

DOSIMETRY- a set of methods for determining (see) ionizing radiation, measuring the levels of radioactive contamination and the effects of radioactive radiation on the human body using (see) ... Big Polytechnic Encyclopedia

- (from Dose and...metry) a field of applied nuclear physics in which physical quantities that characterize the effect of ionizing radiation on various objects are studied (see Radiation dose) ... Big Encyclopedic Dictionary

DOSIMETRY- ionizing radiation, a field of applied nuclear physics that studies physical quantities characterizing the effect of ionizing radiation on the environment, including biological objects (organisms, tissues), as well as methods and means for... ... Veterinary encyclopedic dictionary

DOSIMETRY, DOSIMETRY, and; and. [from Greek dosis dose and metreō measure] 1. A set of methods for determining the dose of radioactive radiation. 2. The field of applied physics in which physical quantities characterizing the action of ionizing ... ... are studied. encyclopedic Dictionary

An area of ​​applied physics in which physical quantities are studied that characterize the effect of ionizing radiation (See Ionizing radiation) on objects of living and inanimate nature, in particular doses (See Dose) of radiation, as well as methods and... ... Great Soviet Encyclopedia

- (see ..metry) a set of methods for determining the dose of ionizing radiation, levels of radioactive contamination, the impact of radioactive radiation on the human body, etc.; Dosimetric measurements are carried out with dosimeters. New dictionary... ... Dictionary of foreign words of the Russian language

dosimetry- I dosime/triya = dosimetry/i; (from the Greek dósis dose and metréō measure) 1) A set of methods for determining the dose of radioactive radiation. 2) The field of applied physics in which physical quantities characterizing the action of ionizing ... ... are studied. Dictionary of many expressions

G. A set of methods for determining the dose of ionizing radiation, the level of radioactive contamination, the effects of radioactive radiation on the human body, animal body, etc. Ephraim's explanatory dictionary. T. F. Efremova. 2000... Modern explanatory dictionary of the Russian language by Efremova

Radiometry- detection and measurement of the number of decays of atomic nuclei in radioactive sources or some of their fraction by the radiation emitted by the nuclei.

Dosimetry- measurement of dissipation and absorption of ionizing radiation energy in a specific material. The radiation dose is determined by the energy and type of incident radiation, as well as the nature of the absorbing material.

Dosimetry and radiometry are aimed at solving different problems, but they are united by common methodological principles for detecting and recording ionizing radiation. Depending on the nature of the tasks, instruments for measuring ionizing radiation are divided into three groups:

1) radiometers designed to measure the activity of radioactive substances, the flux density of ionizing radiation, the specific and volumetric activity of gases, liquids, aerosols, various environmental objects, food products, as well as specific surface activity;

2) dosimeters are designed to measure the exposure dose of X-ray and y-radiation, the absorbed dose of radiation, the exposure dose rate of X-ray and y-radiation, the absorbed dose rate and the intensity of ionizing radiation;

3) spectrometers are designed to measure the distribution of radiation by energy, charge and mass, as well as the spatiotemporal distribution of radiation.

Let's consider methods for recording ionizing radiation:

1. Ionization method is based on measuring the effect of interaction of radiation with matter - ionization of the gas filling the recording device.

Ionization radiation detectors are a charged electrical capacitor (electrodes) placed in a sealed chamber filled with air or gas to create an electric field in the chamber. Charged particles (a or p) entering the detector chamber produce primary ionization of the gaseous medium in it; The y-quanta first produce fast electrons in the detector wall, which then cause ionization of the gas in the chamber. As a result of the formation of ion pairs, the gas becomes a conductor of electric current. In the absence of voltage on the electrodes, all the ions that appeared during primary ionization turn into neutral molecules, and when the voltage increases under the influence of the electric field, the ions begin to move directionally, i.e. an ionization current occurs. The current strength serves as a measure of the amount of radiation and can be recorded by the device. -

At a certain voltage value, all ions formed during radiation reach the electrodes, and as the voltage increases, the current does not increase, i.e. a saturation current region appears. The strength of the saturation ionization current in a given region depends on the number of primary ion pairs created by nuclear radiation in the detector chamber. Ionization chambers operate under these conditions.

With a further increase in voltage, the current increases again, since the ions formed by radiation, especially electrons, when moving towards the electrodes, acquire accelerations sufficient to cause ionization themselves due to collisions with atoms and gas molecules. This process is called impact or secondary ionization. This voltage region is called the proportionality region, i.e. a region where there is strict proportionality between the number of primarily formed ions and the total amount of ions involved in the creation of the ionization current. Proportional counters operate in this mode.

With a further increase in voltage, the strength of the ionization current no longer depends on the number of primary ion pairs. Gas enhancement increases so much that when any nuclear particle appears, an independent gas discharge occurs. This voltage region is called the Geiger region; Geiger-Müller counters operate in this mode.

2. Scintillator method is based on registration of light flashes (scintillations) by a photomultiplier tube (PMT),
arising in some substances (scintillators) under the influence of radiation. Based on their composition, scintillators are divided into inorganic and
organic, and according to their state of aggregation - into solid, plastic, liquid and gas.

Of the inorganic scintillators for recording radiation, sodium iodide (cesium), activated by thalium - Nal (T1), as well as calcium tungstate CaWO, are widely used, since they can be obtained in the form of large single crystals. Scintillators made of lithium iodide -Lil (Sn) are used to register neutrons.

Organic scintillators are represented by the following compounds: single crystals of anthracene ScHu, stibylene C M Hi 2, etc.; plastics (based on polystyrene and polyvinyltoluene); liquid phosphorus (terfinil solution) and inert gases - helium, argon, neon, etc.

4. Luminescent method is based on the accumulation of part of the energy of absorbed ionizing radiation and its release in the form of light glow after additional exposure to ultraviolet radiation (or visible light) or heating. Under the influence of radiation, photoluminescence centers containing silver atoms and ions are created in the phosphor (alkali-halide compounds such as LiF, Nal, phosphate glasses activated by silver). Subsequent illumination of the phosphors with ultraviolet light causes visible luminescence, the intensity of which in the range of 0.1-10 Gy is proportional to the dose, then reaches a maximum (at 350 Gy), and decreases with a further increase in the dose.

5. Photographic method based on the ability of emission when interacting with silver halides (AgBr or AgCI)
photographic emulsion to restore metallic silver similar to visible light, which, after development, is released as blackening. In this case, the degree of blackening of the photographic plate is proportional to the radiation dose.

4. Chemical method is based on measuring the number of molecules or ions (radiation-chemical yield) that are formed or have undergone a change when a substance absorbs radiation.

In chemical dosimeters, substances are selected with the yield of a chemical reaction proportional to the absorbed energy of ionizing radiation. Currently, a ferrosulfate dosimeter is widely used, based on the oxidation reaction of divalent iron into ferric iron under the influence of radiation.