How is radiation dose measured? Units of measurement of radioactive radiation. Consequences of exposure to radioactive waves

1. Dosimetry. Radiation doses. Dose rate.

2. Biological effects of radiation doses. Limit doses.

3. Dosimetric instruments. Detectors ionizing radiation.

4. Methods of protection against ionizing radiation.

5. Basic concepts and formulas.

6. Tasks.

34.1. Dosimetry. Radiation doses. Dose rate

Necessity quantification effects of ionizing radiation on various living and inanimate nature led to the emergence of dosimetry.

Dosimetry - chapter nuclear physics and measuring technology, in which they study 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 ratio energyΔ 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 dose of man-made radiation, which 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.

On globe there are places 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 supplied 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 metal layer (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 personal protection respiratory organs from radioactive dust are used 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 when food products are contaminated, they 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 specific activity 2x10 11 Ci/l and more cannot be consumed.

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

34.5. Basic concepts and formulas

Continuation of the table

End of the 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 with a dose of γ-radiation X = 600 R? Specific heat 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 - radiation from air should not be taken into account.

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

The human body absorbs the energy of ionizing radiation, and the degree of radiation damage depends on the amount of energy absorbed. To characterize the absorbed energy of ionizing radiation per unit mass of a substance, the concept of absorbed dose is used.

Absorbed dose - this is the amount of ionizing radiation energy absorbed by the irradiated body (body tissues) and calculated per unit mass of this substance. The unit of absorbed dose in the International System of Units (SI) is the gray (Gy).

1 Gy = 1 J/kg

For evaluation, they also use a non-systemic unit - Rad. Rad - derived from the English “radiationabsorbeddoze” - absorbed dose of radiation. This is radiation in which every kilogram of mass of matter (say, human body) absorbs 0.01 J of energy (or 1 g of mass absorbs 100 erg).

1 Rad = 0.01 J/kg 1 Gy = 100 Rad

Exposure dose

To assess the radiation situation on the ground, in working or living quarters, caused by exposure to X-ray or gamma radiation, use exposure dose irradiation. In the SI system, the unit of exposure dose is coulomb per kilogram (1 C/kg).

In practice, a non-systemic unit is more often used - x-ray (R). 1 roentgen is a dose of x-rays (or gamma rays) at which 2.08 x 10 9 pairs of ions are formed in 1 cm 3 of air (or in 1 g of air - 1.61 x 10 12 pairs of ions).

1 P = 2.58 x 10 -3 C/kg

An absorbed dose of 1 Rad corresponds to an exposure dose approximately equal to 1 roentgen: 1 Rad = 1 R

Equivalent dose

When living organisms are irradiated, various biological effects occur, the difference between which at the same absorbed dose is explained by different types of irradiation.

To compare the biological effects caused by any ionizing radiation with the effects of X-ray and gamma radiation, the concept of equivalent dose. The SI unit of equivalent dose is the sievert (Sv). 1 Sv = 1 J/kg

There is also a non-systemic unit of equivalent dose of ionizing radiation - the rem (biological equivalent of an x-ray). 1 rem is a dose of any radiation that produces the same biological effect as 1 roentgen of x-ray or gamma radiation.

1 rem = 1 R 1 Sv = 100 rem

The coefficient showing how many times the assessed type of radiation is more biologically dangerous than x-ray or gamma radiation at the same absorbed dose is called radiation quality factor (K).

For X-ray and gamma radiation K=1.

1 Rad x K = 1 rem 1 Gy x K = 1 Sv

All other things being equal, the dose of ionizing radiation is greater, the longer the irradiation time, i.e. the dose accumulates over time. The dose per unit time is called dose rate. If we say that the exposure dose rate of gamma radiation is 1 R/h, this means that in 1 hour of irradiation a person will receive a dose equal to 1 R.

Radioactive source activity (radionuclide) is a physical quantity characterizing the number of radioactive decays per unit time. The more radioactive transformations occur per unit of time, the higher the activity. In the C system, the unit of activity is the becquerel (Bq) - the amount of radioactive substance in which 1 decay occurs in 1 second.

Another unit of radioactivity is the curie. 1 curie is the activity of such an amount of radioactive substance in which 3.7 x 10 10 decays occur per second.

The time during which the number of atoms of a given radioactive substance is reduced by half due to decay is called half-life . The half-life can vary widely: for uranium-238 (U) – 4.47 ppb. years; uranium-234 – 245 thousand years; radium-226 (Ra) – 1600 years; iodine-131 (J) – 8 days; radon-222 (Rn) – 3.823 days; polonium-214 (Po) – 0.000164 sec.

Among the long-lived isotopes released into the atmosphere as a result of the explosion of the nuclear power plant in Chernobyl, there are strontium-90 and cesium-137, the half-lives of which are about 30 years, so the Chernobyl nuclear power plant zone will be unsuitable for normal life for many decades.

RADIATION RISK COEFFICIENTS

It should be taken into account that some parts of the body (organs, tissues) are more sensitive than others: for example, with the same equivalent dose of radiation, cancer is more likely to occur in the lungs than in the thyroid gland, and irradiation of the gonads is especially dangerous due to the risk of genetic damage. Therefore, irradiation doses to organs and tissues should be taken into account with different coefficients. Taking the radiation risk coefficient of the whole organism as one, for different tissues and organs the radiation risk coefficients will be as follows:

0.03 – bone tissue; 0.03 – thyroid gland;

0.12 – light; 0.12 – red bone marrow;

0.15 – mammary gland; 0.25 – ovaries or testes;

0.30 – other fabrics.

RADIATION DOSES RECEIVED BY HUMAN

Populations in any region of the globe are exposed to ionizing radiation every day. This is, first of all, the so-called background radiation of the Earth, which consists of:

cosmic radiation coming to Earth from Space;

radiation from natural radioactive elements found in soil, building materials, air and water;

radiation from natural radioactive substances that enter the body with food and water, are fixed by tissues and stored in the human body.

In addition, people encounter artificial sources of radiation, including radioactive nuclides (radionuclides), created by human hands and used in the national economy.

On average, the radiation dose from all natural sources of ionizing radiation is about 200 mR per year, although this value can vary in different regions of the globe from 50 to 1000 mR/year or more (Table 1). The dose received from cosmic radiation depends on altitude; the higher above sea level, the greater the annual dose.

Table 1

Natural sources of ionizing radiation

Sources	Average annual dose		Contribution to dose
1. Space (sea level radiation)
2. Earth (soil, water, building materials)
3. Radioactive elements contained in the tissues of the human body (K, C, etc.)
4. Other sources
Average total annual dose

Artificial sources of ionizing radiation (Table 2):

medical diagnostic and treatment equipment;

people who constantly use the aircraft are additionally exposed to minor radiation;

nuclear and thermal power plants (the dose depends on the proximity of their location);

phosphate fertilizers;

Buildings made of stone, brick, concrete, wood - poor indoor ventilation can increase the radiation dose caused by inhaling the radioactive gas radon, which is formed during the natural decay of radium contained in many rocks and building materials, as well as in the soil. Radon is invisible, tasteless and odorless heavy gas(7.5 times heavier than air), etc.

Every inhabitant of the Earth throughout his life is annually exposed to a dose of an average of 250-400 mrem.

It is considered safe for a person to accumulate a radiation dose of no more than 35 rem over his entire life. At radiation doses of 10 rem, no changes are observed in the organs and tissues of the human body. With a single irradiation dose of 25-75 rem, short-term minor changes in blood composition are clinically determined.

When irradiated with a dose of more than 100 rem, the development of radiation sickness is observed:

100 – 200 rem – I degree (light);

200 – 400 rem – II degree (average);

400 – 600 rem – III degree (severe);

more than 600 rem – IV degree (extremely severe).

5. Radiation doses and units of measurement

The effect of ionizing radiation is a complex process. The effect of radiation depends on the magnitude of the absorbed dose, its power, type of radiation, and the volume of irradiation of tissues and organs. To quantify it, special units have been introduced, which are divided into non-system units and units in the SI system. Nowadays, SI units are predominantly used. Below in Table 10 is a list of units of measurement of radiological quantities and a comparison of SI units and non-systemic units.

Table 10.

Basic radiological quantities and units
Magnitude	Name and designation units of measurement		Relationships between units
	Off-system	Si
Nuclide activity, A	Curie (Ci, Ci)	Becquerel (Bq, Bq)	1 Ci = 3.7 10 10 Bq 1 Bq = 1 dispersion/s 1 Bq=2.7·10 -11 Ci
Exposition dose, X	X-ray (P, R)	pendant/kg (C/kg, C/kg)	1 Р=2.58·10 -4 C/kg 1 C/kg=3.88·10 3 R
Absorbed dose, D	Glad (rad, rad)	Gray (Gr, Gy)	1 rad-10 -2 Gy 1 Gy=1 J/kg
Equivalent dose, N	Rem (rem, rem)	Sievert (Sv, Sv)	1 rem=10 -2 Sv 1 Sv=100 rem
Integral radiation dose	Rad-gram (rad g, rad g)	Gray-kg (Gy kg, Gy kg)	1 rad g=10 -5 Gy kg 1 Gy kg=105 rad g

To describe the effect of ionizing radiation on matter, we use the following concepts and units of measurement:
Radionuclide activity in the source (A). Activity is equal to the ratio of the number of spontaneous nuclear transformations in this source over a short time interval (dN) to the value of this interval (dt):

The SI unit of activity is Becquerel (Bq).
The extra-systemic unit is the Curie (Ci).

The number of radioactive nuclei N(t) of a given isotope decreases over time according to the law:

N(t) = N 0 exp(-tln2/T 1/2) = N 0 exp(-0.693t /T 1/2)

where N 0 is the number of radioactive nuclei at time t = 0, T 1/2 is the half-life - the time during which half of the radioactive nuclei decay.
The mass m of a radionuclide with activity A can be calculated using the formula:

m = 2.4·10 -24 × M×T 1/2×A,

where M is the mass number of the radionuclide, A is the activity in Becquerels, T 1/2 is the half-life in seconds. The mass is obtained in grams.
Exposure dose (X). As a quantitative measure of X-ray and -radiation, it is customary to use the exposure dose in off-system units, determined by the charge of secondary particles (dQ) formed in the mass of matter (dm) with complete deceleration of all charged particles:

The unit of exposure dose is Roentgen (R). X-ray is the exposure dose of X-ray and
- radiation created in 1 cubic cm of air at a temperature of O°C and a pressure of 760 mm Hg. the total charge of ions of the same sign into one electrostatic unit of electricity. Exposure dose 1 R
corresponds to 2.08·10 9 pairs of ions (2.08·10 9 = 1/(4.8·10 -10)). If we take the average energy of formation of 1 pair of ions in air equal to 33.85 eV, then with an exposure dose of 1 P one cubic centimeter energy transferred to the air is equal to:
(2.08·10 9)·33.85·(1.6·10 -12) = 0.113 erg,
and one gram of air:
0.113/air = 0.113/0.001293 = 87.3 erg.
Absorption of ionizing radiation energy is the primary process that gives rise to a sequence of physicochemical transformations in irradiated tissue, leading to the observed radiation effect. Therefore, it is natural to compare the observed effect with the amount of energy absorbed or dose absorbed.
Absorbed dose (D)- basic dosimetric quantity. It is equal to the ratio of the average energy dE transferred by ionizing radiation to a substance in an elementary volume to the mass dm of the substance in this volume:

The unit of absorbed dose is Gray (Gy). The extrasystemic unit Rad was defined as the absorbed dose of any ionizing radiation equal to 100 erg per 1 gram of irradiated substance.
Equivalent dose (N). To assess the possible damage to human health under conditions of chronic exposure in the field of radiation safety, the concept of an equivalent dose H, equal to the product of the absorbed dose D r created by radiation - r and averaged over the analyzed organ or over the entire body, was introduced by the weighting factor w r (also called the coefficient radiation quality)
(Table 11).

The unit of equivalent dose is Joule per kilogram. It has a special name Sievert (Sv).

Table 11.

Radiation weighting factors
Type of radiation and energy range	Weight multiplier
Photons of all energies
Electrons and muons of all energies
Neutrons with energy< 10 КэВ
Neutrons from 10 to 100 KeV
Neutrons from 100 KeV to 2 MeV
Neutrons from 2 MeV to 20 MeV
Neutrons > 20 MeV
Protons with energies > 2 MeV (except recoil protons)
alpha particles, fission fragments and other heavy nuclei

The effect of radiation is uneven. To assess damage to human health due to of various nature influence of irradiation on different organs (under conditions of uniform irradiation of the whole body), the concept of effective equivalent dose E eff was introduced, used in assessing possible stochastic effects - malignant neoplasms.
Effective dose equal to the sum of weighed equivalent doses in all organs and tissues:

where w t is the tissue weight factor (Table 12), and H t is the equivalent dose absorbed in
fabrics - t. The unit of effective equivalent dose is the sievert.

Table 12.

Values ​​of tissue weight factors w t for various organs and tissues.
Tissue or organ	w t	Tissue or organ	w t
Sex glands	0.20	Liver	0.05
Red bone marrow	0.12	Esophagus	0.05
Large intestine	0.12	Thyroid gland	0.05
Lungs	0.12	Leather	0.01
Stomach	0.12	Surface of bones	0.01
Bladder	0.05	Other organs	0.05
Mammary glands	0.05

Collective effective equivalent dose. To assess damage to the health of personnel and the population from stochastic effects caused by ionizing radiation, the collective effective equivalent dose S is used, defined as:

where N(E) is the number of persons who received an individual effective equivalent dose E. The unit of S is the person-Sievert
(person-Sv).
Radionuclides- radioactive atoms with a given mass number and atomic number, and for isomeric atoms - with a given specific energy state of the atomic nucleus. Radionuclides
(and non-radioactive nuclides) of an element are otherwise called its isotopes.
In addition to the above values, to compare the degree of radiation damage to a substance when it is exposed to various ionizing particles with different energies, the value of linear energy transfer (LET), determined by the relation:

where is the average energy locally transferred to the medium by an ionizing particle due to collisions along the elementary path dl.
Threshold energy usually refers to the energy of the electron. If in a collision event a primary charged particle forms an -electron with an energy greater than , then this energy is not included in the value of dE, and the -electrons with energy are more considered as independent primary particles.
The choice of threshold energy is arbitrary and depends on specific conditions.
From the definition it follows that linear energy transfer is some analogue of the stopping power of a substance. However, there is a difference between these quantities. It consists of the following:
1. LET does not include energy converted into photons, i.e. radiation losses.
2. At a given threshold, the LET does not include the kinetic energy of particles exceeding .
The values ​​of LET and stopping power coincide if we can neglect losses due to bremsstrahlung and

Table 13.

Average values ​​of linear energy transfer L and range R for electrons, protons and alpha particles in soft tissue.
Particle	E, MeV	L, keV/µm	R, µm
Electron	0.01	2.3	1
	0.1	0.42	180
	1.0	0.25	5000
Proton	0.1	90	3
	2.0	16	80
	5.0	8	350
	100.0	4	1400
α -particle	0.1	260	1
	5.0	95	35

Based on the magnitude of linear energy transfer, the weighting factor of this type of radiation can be determined (Table 14)

Table 14.

Dependence of the radiation weight factor w r on linear transfer of energy of ionizing radiation L to water.
L, keV/µm	< 3/5	7	23	53	> 175
w r	1	2	5	10	20

Maximum permissible radiation doses

In relation to exposure to radiation, the population is divided into 3 categories.
Category A exposed persons or personnel ( professional workers) - persons who permanently or temporarily work directly with sources of ionizing radiation.
Category B exposed persons or a limited part of the population - persons who do not work directly with sources of ionizing radiation, but due to their living conditions or workplace location may be exposed to ionizing radiation.
Category B exposed persons or population - the population of a country, republic, region or region.
For category A, maximum permissible doses are introduced - the highest values ​​of the individual equivalent dose per calendar year, at which uniform exposure over 50 years cannot cause adverse changes in health that are detectable modern methods. For category B, a dose limit is determined.
Three groups of critical organs are established:
Group 1 - the whole body, gonads and red bone marrow.
Group 2 - muscles, thyroid gland, adipose tissue, liver, kidneys, spleen, gastrointestinal tract, lungs, eye lenses and other organs, with the exception of those belonging to groups 1 and 3.
Group 3 - skin, bone tissue, hands, forearms, legs and feet.
Radiation dose limits for different categories of persons are given in Table 15.

Table 15.

Dose limits of external and internal exposure (rem/year).
	Critical Organ Groups
	1	2	3
Category A, maximum permissible dose (MAD)	5	15	30
Category B, dose limit (LD)	0.5	1.5	3

In addition to the main dose limits, derivative standards and reference levels are used to assess the effects of radiation. The standards are calculated taking into account the non-exceeding of dose limits MDA (maximum permissible dose) and PD (dose limit). Calculation of the permissible content of a radionuclide in the body is carried out taking into account its radiotoxicity and non-exceeding of the maximum permissible limits in a critical organ. Control levels should provide such low levels exposures that can be achieved subject to basic dose limits.
For category A (personnel) the following is established:
- maximum permissible annual intake of radionuclide through the respiratory system;
- permissible radionuclide content in the critical organ DS A;
- permissible radiation dose rate DMD A;
- permissible particle flux density DPP A;
- permissible volumetric activity (concentration) of the radionuclide in the air of the working area of ​​DK A;
- permissible contamination of skin, protective clothing and working surfaces of DZ A.
For category B (limited part of the population) the following are established:
- limit of annual intake of GGP radionuclide through the respiratory or digestive organs;
- permissible volumetric activity (concentration) of radionuclide DK B in atmospheric air and water;
- permissible dose rate DMD B;
- permissible particle flux density DPP B;
- acceptable contamination of skin, clothing and surfaces of DZ B.
Numerical values ​​of permissible levels are contained in full in
"Radiation Safety Standards".

After beta radiation and alpha radiation were discovered, the question of assessing these radiations in interaction with the environment became a question. The exposure dose for assessing these radiations turned out to be unsuitable, since the degree of ionization from them turned out to be different in the air, in various irradiated substances and in biological tissue. Therefore, a universal characteristic was proposed - absorbed dose.

Absorbed dose is the amount of energy E transferred to a substance by ionizing radiation of any kind, calculated per unit mass m of any substance.

In other words, the absorbed dose (D) is the ratio of the energy dE, which is transferred to a substance by ionizing radiation in an elementary volume, to the mass dm of the substance in this volume:

1 J/kg = 1 Gray. The extra-systemic unit is rad (radiation adsorption dose). 1 Gray = 100 rad.

You can also use fractional unit values, for example: mGy, μGy, mrad, μrad, etc.

Note. According to RD50-454-84, the use of the “rad” unit is not recommended. However, in practice there are instruments with this calibration, and it is still in use.

The definition of absorbed dose includes the concept of average energy transferred to a substance in a certain volume. The fact is that due to the statistical nature of radiation and the probabilistic nature of the interaction of radiation with matter, the amount of energy transferred to matter is subject to fluctuations. It is impossible to predict its value during measurement in advance. However, after carrying out a series of measurements, it is possible to obtain the average value of this value.

Dose in an organ or biological tissue (D,r) - the average absorbed dose in a specific organ or tissue of the human body:

D T = E T /m T ,(4)

where E T - total energy, transmitted by ionizing radiation to tissue or organ; m T is the mass of an organ or tissue.

When a substance is irradiated, the absorbed dose increases. The rate of dose increase is characterized by the absorbed dose rate.

The absorbed dose rate of ionizing radiation is the ratio of the increment in the absorbed dose of radiation dD over the time interval dt to this interval:

Dose rate units: rad/s, Gy/s, rad/h, Gy/h, etc.

The absorbed dose rate in a number of cases can be considered as a constant value over a short time interval or changing exponentially over a significant time interval, then we can assume that:

Kerma is an abbreviation of English words translated as “kinetic energy of weakening in a material.” The characteristic is used to assess the impact of indirectly ionizing radiation on the environment. Kerma is the ratio of the sum of the initial kinetic energies dE k of all charged particles formed indirectly by radiation in an elementary volume to the mass dm of the substance in this volume:

K = dE k /dm. (7)

Units of measurement in SI and non-systemic: Gray and rad, respectively.

Kerma was introduced to more fully take into account the radiation field, in particular the energy flux density, and is used to assess the impact of indirectly ionizing radiation on the environment.

Equivalent dose

It has been established that when human biological tissue is irradiated with the same energy (that is, when receiving the same dose), but with different types of rays, the health consequences will be different. For example, when the human body is irradiated with alpha particles, the likelihood of developing cancer is much higher than when irradiated with beta particles or gamma rays. Therefore, a characteristic was introduced for biological tissue - an equivalent dose.

Equivalent dose (HTR) is the absorbed dose in an organ or tissue multiplied by the corresponding radiation quality factor WR of a given type of radiation R.

Introduced to assess the consequences of irradiation of biological tissue with low doses (doses not exceeding 5 maximum permissible doses for irradiation of the entire human body), that is, 250 mSv/year. It cannot be used to assess the effects of high dose exposure.

The equivalent dose is:

H T . R = D T . R · W R ,(8)

where D T . R is the dose absorbed by biological tissue by radiation R; W R - weight factor (quality factor) of radiation R (alpha particles, beta particles, gamma rays, etc.), taking into account the relative efficiency various types radiation in inducing biological effects (Table 1). This multiplier depends on many factors, in particular on the magnitude of linear energy transfer, on the ionization density along the track of the ionizing particle, etc.

Formula (8) is valid for assessing doses of both external and internal irradiation of only individual organs and tissues or uniform irradiation of the entire human body.

When exposed to different types of radiation simultaneously with different weighting factors, the equivalent dose is determined as the sum of the equivalent doses for all these types of radiation R:

H T = Σ H T . R (9)

It has been established that at the same absorbed dose, the biological effect depends on the type of ionizing radiation and the radiation flux density.

Note. When using formula (8), the average quality factor is taken in a given volume of biological tissue of standard composition: 10.1% hydrogen, 11.1% carbon, 2.6% nitrogen, 76.2% oxygen.

The SI unit of equivalent dose is Sievert (Sv).

Sievert is a unit of equivalent dose of radiation of any nature in biological tissue, which creates the same biological effect as the absorbed dose of 1 Gy of standard X-ray radiation with a photon energy of 200 keV. Fractional units are also used - μSv, mSv. There is also a non-systemic unit - the rem (biological equivalent of the rad), which is gradually being withdrawn from use.

1 Sv = 100 rem.

Fractional units are also used - mrem, µrem.

Table 1. Radiation quality factors

Type of radiation and energy range	WE quality factors
Photons of all energies
Electrons of all energies
Neutrons with energy:
from 10 keV to 100 keV
> 100 keV up to 2 msv
> 2 MeV to 20 MeV
Protons with energies greater than 2 MeV, except recoil protons
Alpha particles, fission fragments, heavy nuclei
Note. All values ​​refer to radiation incident on the body and, in the case of internal irradiation, emitted during nuclear transformation.

Note. The WR coefficient takes into account the dependence of the adverse biological effects of low-dose irradiation on the total linear energy transfer (LET) of the radiation. Table 2 shows the dependence of the quality weight coefficient W R on LET.

Table 2. Dependence of quality factor WR on LET

Equivalent dose rate is the ratio of the increment of equivalent dose dH over time dt to this time interval:

Units of equivalent dose rate mSv/s, μSv/s, rem/s, mrem/s, etc.

Many people face difficulties in determining the units of measurement of radioactive radiation and practical use obtained values. Difficulties arise not only because of their great variety: becquerels, curies, sieverts, roentgens, rads, coulombs, rhemes, etc., but also due to the fact that not all quantities used are related to each other by multiple ratios and, if necessary, can be converted from one to another.

How to figure it out?

Everything is quite simple if we separately consider the units associated with radioactivity as a physical phenomenon, and the quantities that measure the impact of this phenomenon (ionizing radiation) on living organisms and environment. And also, if we do not forget about non-systemic units and units of radioactivity operating in the SI system (International System of Units), which was introduced in 1982 and is mandatory for use in all institutions and enterprises.

Non-systemic (old) unit of measurement of radioactivity

The Curie (Ci) is the first unit of radioactivity, measuring the activity of 1 gram of pure radium. Introduced in 1910 and named after the French scientists C. and M. Curie, it is not associated with any measurement system and lately lost her practical significance. In Russia, despite the current SI system, curie is permitted for use in the field of nuclear physics and medicine without a limitation period.

SI units of radioactivity

The SI uses a different quantity, becquerel (Bq), which defines the decay of one nucleus per second. Becquerel is more convenient in calculations than curie, since it has not such large values ​​and allows without complex mathematical operations Based on the radioactivity of a radionuclide, determine its quantity. By calculating the number of decays of 1 g of radon, it is easy to establish the relationship between Ci and Bq: 1 Ci = 3.7*1010 Bq, and also determine the activity of any other radioactive element.

Measurement of ionizing radiation

With the discovery of radium, it was discovered that the radiation of radioactive substances affects living organisms and causes biological effects similar to the effects of x-rays. A concept has emerged called the dose of ionizing radiation - a value that allows one to evaluate the impact of radiation exposure on organisms and substances. Depending on the characteristics of irradiation, equivalent, absorbed and exposure doses are distinguished:

1. Exposure dose is an indicator of air ionization that occurs under the influence of gamma and X-rays, determined by the number of radionuclide ions formed in 1 cubic meter. see air under normal conditions. In the SI system it is measured in coulombs (C), but there is also a non-systemic unit - the roentgen (R). One roentgen is a large value, so in practice it is more convenient to use its parts per million (µR) or thousandth (mR). The following relationships have been established between exposure dose units: 1 P = 2, 58.10-4 C/kg.
2. Absorbed dose is the energy of alpha, beta and gamma radiation absorbed and accumulated by a unit mass of a substance. IN international system The SI has introduced the following unit of measurement for it - the gray (Gy), although in some areas, for example, in radiation hygiene and radiobiology, the non-systemic unit - rad (R) is still widely used. There is the following correspondence between these quantities: 1 Rad = 10-2 Gy.
3. Equivalent dose is the absorbed dose of ionizing radiation, taking into account the degree of its impact on living tissue. Since the same doses of alpha, beta or gamma radiation cause different biological damage, the so-called QC quality factor has been introduced. To obtain an equivalent dose, it is necessary to multiply the absorbed dose received from a certain type of radiation by this coefficient. The equivalent dose is measured in bers (Rem) and sieverts (Sv), both of these units are interchangeable, converted from one to the other in this way: 1 Sv = 100 Rem (Rem).

The SI system uses the sievert - the equivalent dose of a specific ionizing radiation absorbed by one kilogram of biological tissue. To convert grays to sieverts, you should take into account the coefficient of relative biological activity (RBE), which is equal to:

• for alpha particles - 10-20;
• for gamma and beta radiation - 1;
• for protons - 5-10;
• for neutrons with speeds up to 10 keV - 3-5;
• for neutrons with speeds greater than 10 keV: 10-20;
• for heavy nuclei - 20.

rem (biological equivalent of an x-ray) or rem (in English rem - Roentgen Equivalent of Man) - non-systemic unit of equivalent dose. Since alpha radiation causes more damage, to obtain a result in rems, it is necessary to multiply the measured radioactivity in rads by a factor of twenty. When determining gamma or beta radiation, conversion of values ​​is not required, since rems and rads are equal to each other.