To measure quantities characterizing ionizing radiation, the unit “roentgen” was historically the first to appear. This is a measure of the exposure dose to x-rays or gamma radiation. Later, “rad” was added to measure the absorbed dose of radiation.
Radiation dose (absorbed dose) is the energy of radioactive radiation absorbed in a unit of irradiated substance or by a person. As the irradiation time increases, the dose increases. Under the same irradiation conditions, it depends on the composition of the substance. The absorbed dose disrupts physiological processes in the body and in some cases leads to radiation sickness of varying severity. As a unit of absorbed radiation dose, the SI system provides a special unit - gray (Gy). 1 gray is a unit of absorbed dose at which 1 kg. The irradiated substance absorbs energy of 1 joule (J). Therefore 1 Gy = 1 J/kg.
The absorbed dose of radiation is a physical quantity that determines the degree of radiation exposure.
Dose rate (absorbed dose rate) – dose increment per unit time. It is characterized by the rate of dose accumulation and can increase or decrease over time. Its unit in the C system is gray per second. This is the absorbed dose rate of radiation at which in 1 s. a radiation dose of 1 Gy is created in the substance. In practice, to estimate the absorbed dose of radiation, an off-system unit of absorbed dose rate is still widely used - rad per hour (rad/h) or rad per second (rad/s).
Equivalent dose. This concept was introduced to quantify adverse biological effects various types radiation. It is determined by the formula Deq = Q*D, where D is the absorbed dose of a given type of radiation, Q is the radiation quality factor, which for various types of ionizing radiation with an unknown spectral composition is accepted for X-ray and gamma radiation-1, for beta radiation- 1, for neutrons with energy from 0.1 to 10 MeV-10, for alpha radiation with energy less than 10 MeV-20. From the given figures it is clear that with the same absorbed dose, neutron and alpha radiation cause, respectively, 10 and 20 times greater damaging effects. In the SI system, equivalent dose is measured in sieverts (Sv). A sievert is equal to one gray divided by the quality factor. For Q = 1 we get
1 Sv = 1 Gy = 1 J/k = 100 rad = 100 rem.
Q Q Q
A rem (biological equivalent of an x-ray) is a non-systemic unit of equivalent dose, such an absorbed dose of any radiation that causes the same biological effect as 1 x-ray of gamma radiation. Since the quality factor of beta and gamma radiation is equal to 1, then on the ground, contaminated with radioactive substances under external irradiation of 1 Sv = 1 Gy; 1 rem = 1 rad; 1 rad » 1 R.
From this we can conclude that the equivalent, absorbed and exposure doses for people wearing protective equipment in a contaminated area are almost equal.
Equivalent dose rate is the ratio of the increment of equivalent dose over a certain time interval. Expressed in sieverts per second. Since the time a person remains in the radiation field at acceptable levels is usually measured in hours, it is preferable to express the equivalent dose rate in microsieverts per hour.
According to the conclusion of the International Commission on Radiation Protection, harmful effects in humans can occur at equivalent doses of at least 1.5 Sv/year (150 rem/year), and in cases of short-term exposure - at doses above 0.5 Sv (50 rem). When radiation exposure exceeds a certain threshold, radiation sickness occurs.
The equivalent dose rate generated by natural radiation (terrestrial and cosmic origin) ranges from 1.5 to 2 mSv/year and plus artificial sources (medicine, radioactive fallout) from 0.3 to 0.5 mSv/year. So it turns out that a person receives from 2 to 3 mSv per year. These figures are approximate and depend on specific conditions. According to other sources, they are higher and reach 5 mSv/year.
Exposure dose is a measure of the ionization effect of photon radiation, determined by the ionization of air under conditions of electronic equilibrium.
The SI unit of exposure dose is one coulomb per kilogram (C/kg). The extrasystemic unit is the roentgen (R), 1R – 2.58*10-4 C/kg. In turn, 1 C/kg » 3.876 * 103 R. For convenience in work, when recalculating the numerical values of the exposure dose from one system of units to another, tables available in the reference literature are usually used.
Exposure dose rate is the increment of exposure dose per unit time. Its SI unit is ampere per kilogram (A/kg). However, during the transition period, you can use a non-systemic unit - roentgens per second (R/s).
1 R/s = 2.58*10-4 A/kg
It must be remembered that after January 1, 1990, it is not recommended to use the concept of exposure dose and its power at all. Therefore, during the transition period, these values should be indicated not in SI units (C/kg, A/kg), but in non-systemic units - roentgens and roentgens per second.
4. radiation dose rate - radiation dose per unit of time - rad/hour, r/hour.
Note. P0 - radiation dose rate t hours after the explosion:
P is the radiation dose rate any time after the explosion.
Since measurements of the radiation dose rate at an object are carried out non-simultaneously, when assessing the radiation situation, it is advisable to calculate their value 1 hour after a nuclear explosion (Table 2).
1 The values of gamma radiation attenuation coefficients (K) by residential buildings are given for rural settlements. In cities, the values of attenuation coefficients for the same buildings will be 20-40% higher due to the attenuation of the dose rate of ionizing radiation nearby standing houses and other ground structures.
Radiation (or ionizing radiation) is the totality of different types physical fields and microparticles that have the ability to ionize substances.
Radiation is divided into several types and measured using various scientific instruments specially designed for this purpose.
In addition, there are units of measurement, exceeding which can be fatal to humans.
The most accurate and reliable ways to measure radiation
Using a dosimeter (radiometer), you can measure the intensity of radiation as accurately as possible and examine a specific place or specific objects. Most often, devices for measuring radiation levels are used in places:
- Close to areas of radiation radiation (for example, near the Chernobyl nuclear power plant).
- Planned residential construction.
- In unexplored, unexplored areas during hikes and travels.
- When potentially purchasing residential properties.
Since it is impossible to clear the territory and objects located on it from radiation (plants, furniture, equipment, structures), the only sure way to protect yourself is to check the level of danger in time and, if possible, stay as far away from sources and contaminated areas. Therefore, under normal conditions, household dosimeters can be used to check the area, products, and household items, which successfully detect the danger and its doses.
Radiation regulation
The purpose of radiation control is not just to measure its level, but also to determine whether the indicators comply with established standards. Criteria and standards for safe levels of radiation are prescribed in separate laws and generally established rules. The conditions for containing man-made and radioactive substances are regulated for the following categories:
- Food
- Air
- Building materials
- Computer equipment
- Medical equipment.
Manufacturers of many types of food or industrial products are required by law to prescribe radiation safety compliance criteria and indicators in their conditions and certification documents. The relevant government services quite strictly monitor various deviations or violations in this regard.
Radiation units
It has long been proven that background radiation is present almost everywhere, it’s just that in most places its level is considered safe. The level of radiation is measured in certain indicators, among which the main ones are doses - units of energy absorbed by a substance at the moment of passage of ionizing radiation through it.
The main types of doses and their units of measurement can be listed in the following definitions:
- Exposure dose– created by gamma or x-ray radiation and shows the degree of ionization of air; non-systemic units of measurement – rem or “roentgen”, in the international SI system it is classified as “coulomb per kg”;
- Absorbed dose– unit of measurement – gray;
- Effective dose– determined individually for each organ;
- Dose equivalent– depending on the type of radiation, calculated based on coefficients.
Radiation radiation can only be determined by instruments. At the same time, there are certain doses and established standards, among which permissible indicators, negative doses of impact on human body and lethal doses.
Radiation Safety Levels
For the population, certain levels of safe values of absorbed radiation doses have been established, which are measured by a dosimeter.
Each territory has its own natural background radiation, but a value equal to approximately 0.5 microsieverts (µSv) per hour (up to 50 microroentgens per hour) is considered safe for the population. Under normal background radiation, the safest level of external irradiation of the human body is considered to be up to 0.2 (µSv) microsievert per hour (a value equal to 20 microroentgens per hour).
Most upper limit permissible radiation level – 0.5 µSv - or 50 µR/h.
Accordingly, a person can tolerate radiation with a power of 10 μS/h (microsievert), and by reducing the exposure time to a minimum, radiation of several millisieverts per hour is harmless. This is the effect of fluorography and x-rays – up to 3 mSv. A photograph of a diseased tooth at the dentist – 0.2 mSv. The absorbed radiation dose has the ability to accumulate throughout life, but the amount should not cross the threshold of 100-700 mSv.
X-ray examinations in medicine still play a leading role. Sometimes without data it is impossible to confirm or make a correct diagnosis. Every year, techniques and X-ray technology are improved, become more complex, and become safer, but, nevertheless, the harm from radiation remains. Minimizing the negative impact of diagnostic radiation is a priority task of radiology.
Our task is to understand, at a level accessible to anyone, the existing figures of radiation doses, their units of measurement and accuracy. Let's also touch on the topic of reality. possible problems health problems that this type of medical diagnosis can cause.
We recommend reading:What is X-ray radiation
X-rays are a stream of electromagnetic waves with wavelengths in the range between ultraviolet and gamma radiation. Each type of wave has its own specific effect on the human body.
At its core, X-ray radiation is ionizing. It has high penetrating ability. Its energy poses a danger to humans. The higher the dose received, the higher the harmfulness of radiation.
About the dangers of exposure to X-ray radiation on the human body
Passing through the tissues of the human body, X-rays ionize them, changing the structure of molecules, atoms, in simple terms - “charging” them. The consequences of the resulting radiation can manifest themselves in the form of diseases in the person himself (somatic complications), or in his offspring (genetic diseases).
Each organ and tissue is affected differently by radiation. Therefore, radiation risk coefficients have been created, which can be seen in the picture. The higher the coefficient value, the higher the tissue’s susceptibility to the effects of radiation, and hence the risk of complications.
The hematopoietic organs most susceptible to radiation are the red bone marrow.
The most common complication that appears in response to radiation is blood pathologies.
A person experiences:
- reversible changes in blood composition after minor amounts of radiation;
- leukemia – a decrease in the number of leukocytes and a change in their structure, leading to disruptions in the body’s functioning, its vulnerability, and decreased immunity;
- thrombocytopenia – a decrease in the content of platelets, blood cells responsible for clotting. This pathological process can cause bleeding. The condition is aggravated by damage to the walls of blood vessels;
- hemolytic irreversible changes in the composition of the blood (decomposition of red blood cells and hemoglobin) as a result of exposure to powerful doses of radiation;
- erythrocytopenia - a decrease in the content of erythrocytes (red blood cells), causing the process of hypoxia (oxygen starvation) in the tissues.
FriendnopathologistsAnd:
- development of malignant diseases;
- premature aging;
- damage to the lens of the eye with the development of cataracts.
Important: X-ray radiation becomes dangerous in case of intensity and duration of exposure. Medical equipment uses low-energy radiation of short duration, so it is considered relatively harmless when used, even if the examination has to be repeated many times.
A single exposure to radiation that a patient receives during conventional radiography increases the risk of developing a malignant process in the future by approximately 0.001%.
note: unlike exposure to radioactive substances, the harmful effects of rays stop immediately after turning off the device.
The rays cannot accumulate and form radioactive substances, which will then become independent sources of radiation. Therefore, after an x-ray, no measures should be taken to “remove” radiation from the body.
In what units are the doses of received radiation measured?
It is difficult for a person far from medicine and radiology to understand the abundance of specific terminology, dose numbers and units in which they are measured. Let's try to bring the information to an understandable minimum.
So how is X-ray dose measured? There are many units of measurement for radiation. We won't go into everything in detail. Becquerel, curie, rad, gray, rem - this is a list of the main quantities of radiation. They are used in different systems measurements and areas of radiology. Let us dwell only on those that are practically significant in x-ray diagnostics.
We will be more interested in X-rays and sieverts.
The level of penetrating radiation emitted by an X-ray machine is measured in a unit called “roentgen” (P).
To evaluate the effect of radiation on humans, the concept was introduced equivalent absorbed dose (EDD). In addition to EPD, there are other types of doses - all of them are presented in the table.
The equivalent absorbed dose (in the picture - Effective equivalent dose) is a quantitative amount of energy that the body absorbs, but it takes into account the biological response of body tissues to radiation. It is measured in sieverts (Sv).
A sievert is approximately comparable to the value of 100 roentgens.
The natural background radiation and doses delivered by medical X-ray equipment are much lower than these values, so they are measured using the values of a thousandth (milli) or one millionth (micro) of Sievert and Roentgen.
In numbers it looks like this:
- 1 sievert (Sv) = 1000 millisievert (mSv) = 1,000,000 microsievert (µSv)
- 1 roentgen (R) = 1000 milliroentgen (mR) = 1,000,000 milliroentgen (µR)
To estimate the quantitative part of the radiation received per unit of time (hour, minute, second), the concept is used - dose rate, measured in Sv/h (sievert-hour), μSv/h (microsievert-hour), R/h (roentgen-hour), μR/h (micro-roentgen-hour). Likewise - in minutes and seconds.
It can be even simpler:
- total radiation is measured in roentgens;
- the dose received by a person is in sieverts.
Radiation doses received in sieverts accumulate over a lifetime. Now let's try to find out how many sieverts a person receives.
Natural radiation background
The level of natural radiation is different everywhere, it depends on the following factors:
- altitude above sea level (the higher, the harder the background);
- geological structure of the area (soil, water, rocks);
- external reasons - the material of the building, the presence of nearby enterprises that provide additional radiation exposure.
Note:The most acceptable background is considered to be one in which the radiation level does not exceed 0.2 μSv/h (microsievert-hour), or 20 μR/h (micro-roentgen-hour)
The upper limit of the norm is considered to be up to 0.5 μSv/h = 50 μR/h.
Over several hours of exposure, a dose of up to 10 μSv/h = 1 mR/h is allowed.
All types of X-ray examinations fit into safe standards for radiation exposure, measured in mSv (millisieverts).
Permissible radiation doses for humans accumulated over a lifetime should not exceed the limits of 100-700 mSv. Actual exposure values for people living at high altitudes may be higher.
On average, a person receives a dose of 2-3 mSv per year.
It is summed up from the following components:
- radiation from the sun and cosmic radiation: 0.3 mSv – 0.9 mSv;
- soil-landscape background: 0.25 – 0.6 mSv;
- radiation from housing materials and buildings: 0.3 mSv and above;
- air: 0.2 – 2 mSv;
- food: from 0.02 mSv;
- water: from 0.01 – 0.1 mSv:
In addition to the external dose of radiation received, the human body also accumulates its own deposits of radionuclide compounds. They also represent a source of ionizing radiation. For example, in bones this level can reach values from 0.1 to 0.5 mSv.
In addition, there is irradiation with potassium-40, which accumulates in the body. And this value reaches 0.1 – 0.2 mSv.
note: To measure background radiation, you can use a conventional dosimeter, for example RADEKS RD1706, which gives readings in sieverts.
Forced diagnostic doses of X-ray irradiation
The amount of equivalent absorbed dose for each x-ray examination may vary significantly depending on the type of examination. The radiation dose also depends on the year of manufacture of the medical equipment and the workload on it.
Important: modern X-ray equipment produces radiation tens of times lower than the previous one. We can say this: the latest digital X-ray technology is safe for humans.
But we will still try to give average figures for the doses that a patient can receive. Let us pay attention to the difference between the data produced by digital and conventional X-ray equipment:
- digital fluorography: 0.03-0.06 mSv (the most modern digital devices produce radiation in a dose of 0.002 mSv, which is 10 times lower than their predecessors);
- film fluorography: 0.15-0.25 mSv, (old fluorographs: 0.6-0.8 mSv);
- X-ray of the chest organs: 0.15-0.4 mSv;
- dental (dental) digital radiography: 0.015-0.03 mSv., conventional: 0.1-0.3 mSv.
In all of these cases we are talking about one picture. Studies in additional projections increase the dose in proportion to the frequency of their conduct.
The fluoroscopic method (involves not photographing an area of the body, but a visual examination by a radiologist on a monitor screen) produces significantly less radiation per unit of time, but the total dose may be higher due to the duration of the procedure. Thus, for 15 minutes of chest X-ray, the total dose of radiation received can be from 2 to 3.5 mSv.
Diagnosis of the gastrointestinal tract – from 2 to 6 mSv.
Computed tomography applies doses ranging from 1-2 mSv to 6-11 mSv, depending on the organs being examined. The more modern the X-ray machine is, the lower the doses it gives.
We especially note radionuclide diagnostic methods. One radiotracer-based procedure produces a total dose of 2 to 5 mSv.
A comparison of the effective doses of radiation received during the most commonly used diagnostic tests in medicine and the doses received daily by humans from the environment is presented in the table.
| Procedure | Effective radiation dose | Comparable to natural exposure received over a specified period of time |
| Chest X-ray | 0.1 mSv | 10 days |
| Fluorography of the chest | 0.3 mSv | 30 days |
| Computed tomography of the abdominal cavity and pelvis | 10 mSv | 3 years |
| Whole body computed tomography | 10 mSv | 3 years |
| Intravenous pyelography | 3 mSv | 1 year |
| X-ray of the stomach and small intestine | 8 mSv | 3 years |
| X-ray of the large intestine | 6 mSv | 2 years |
| X-ray of the spine | 1.5 mSv | 6 months |
| X-ray of the bones of the arms or legs | 0.001 mSv | less than 1 day |
| Computed tomography - head | 2 mSv | 8 months |
| Computed tomography – spine | 6 mSv | 2 years |
| Myelography | 4 mSv | 16 months |
| Computed tomography – chest organs | 7 mSv | 2 years |
| Vaccine cystourethrography | 5-10 years: 1.6 mSv Infant: 0.8 mSv |
6 months 3 months |
| Computed tomography – skull and paranasal sinuses | 0.6 mSv | 2 months |
| Bone densitometry (density determination) | 0.001 mSv | less than 1 day |
| Galactography | 0.7 mSv | 3 months |
| Hysterosalpingography | 1 mSv | 4 months |
| Mammography | 0.7 mSv | 3 months |
Important:Magnetic resonance imaging does not use x-rays. In this type of study, an electromagnetic pulse is sent to the diagnosed area, exciting the hydrogen atoms of the tissues, then the response that causes them is measured in the generated magnetic field with a high intensity level.Some people mistakenly classify this method as X-ray.
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 1) a list of units of measurement of radiological quantities is given and a comparison of SI units and non-systemic units is made.
Table 1.
|
Basic radiological quantities and units |
|||
|
Magnitude |
Name and designation of the unit of measurement |
Relationships between units |
|
|
Off-system |
|||
|
Nuclide activity, A |
Curie (Ci, Ci) |
Becquerel (Bq, Bq) |
|
|
Exposure dose, X |
X-ray (P, R) |
Coulomb/kg (C/kg, C/kg) |
1 R=2.58*10-4 C/kg1 C/kg=3.88*103 R |
|
Absorbed dose, D |
Glad (rad, rad) |
Gray (Gr, Gy) |
1 rad-10-2 Gy1 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*kg1 Gy*kg=105 rad*g |
To describe the effect of ionizing radiation on matter, the following concepts and units of measurement are used:
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 with time according to the law:
N(t) = N0 exp(-tln2 / T1/2) = N0 exp(-0.693t / T1/2)
where No is the number of radioactive nuclei at time t = 0, T1/2 half-life is 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 T1/2 A
where M is the mass number of the radionuclide, A is the activity in Becquerels, T1/2 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 an 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.
The exposure dose of 1 R corresponds to 2.08*109 ion pairs (2.08*109 = 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, energy is transferred to one cubic centimeter of air equal to:
(2.08*109)*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) is the main 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 Dr created by radiation - r and averaged over the analyzed organ or over the entire body, was introduced by the weighting factor wr (also called the quality factor radiation) (Table 2).
The unit of equivalent dose is Joule per kilogram. It has a special name Sievert (Sv).
Table 2.
|
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) |
|
|
Particles, fission fragments and other heavy nuclei |
The effect of radiation is uneven. To assess the damage to human health due to the different nature of the influence of radiation on different organs (under conditions of uniform irradiation of the whole body), the concept of effective equivalent dose E eff was introduced, which is used in assessing possible stochastic effects - malignant neoplasms.
The effective dose is equal to the sum of weighed equivalent doses in all organs and tissues:
where w t is the tissue weight factor (Table 3), and H t is the equivalent dose absorbed in the tissue - t. The unit of effective equivalent dose is the sievert.
Table 3
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 man-Sievert (man-Sv).
Radionuclides are 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 also called 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 produces an -electron with more energy, then this energy is not included in the dE value, and -electrons with more energy are 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
ionizing radiation dosimeter
Table 4
Based on the magnitude of linear energy transfer, the weight factor of this type of radiation can be determined (Table 5)
Table 5
Maximum permissible radiation doses according to NRB-99
In relation to radiation exposure, the population is divided into 3 categories:
Category B of 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.
- - main dose limits (LD) given in Table 6;
- - permissible levels of monofactorial exposure (for one radionuclide, route of entry or one type of external exposure), which are derived from the main dose limits: annual intake limits (AGL), permissible average annual volume activities (ADV), annual average specific activities (ASA) and others;
- - control levels (doses, levels, activities, flow densities, etc.). Their values should take into account the level of radiation safety achieved in the organization and provide conditions under which radiation exposure will be below the permissible level.
Table 6 Basic dose limits
Notes:
- * Simultaneous irradiation is allowed up to the specified limits for all standardized values.
- ** The main dose limits, like all other permissible levels of exposure of personnel in group B, are equal to 1/4 of the values for personnel in group A. Further in the text, all standard values for the category of personnel are given only for group A.
- *** Refers to a dose at a depth of 300 mg/cm2.
- **** Refers to the average area of I cm2 value in the basal layer of skin with a thickness of 5 mg/cm2 under the cover layer with a thickness of 5 mg/cm2. On the palms the thickness of the coating layer is 40 mg/cm2. The specified limit allows irradiation of all human skin, provided that within the average irradiation of any 1 cm2 of skin area, this limit is not exceeded. The dose limit when irradiating the skin of the face ensures that the dose limit to the lens from beta particles is not exceeded.
Basic radiation dose limits do not include doses from natural and medical exposures, as well as doses from radiation accidents. There are special restrictions on these types of exposure.
The effective dose for personnel should not exceed 1000 mSv over a working period (50 years), and 70 mSv for the population over a lifetime (70 years). The periods begin on January 1, 2000.
When a person is simultaneously exposed to sources of external and internal radiation, the annual effective dose should not exceed the dose limits established in Table. 6.
Three groups of critical organs are established:
- Group 1 - the whole body, gonads and red bone marrow;
- Group 2 - muscles, thyroid, 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 7.
Table 7
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. Reference levels should provide exposure levels as low as can be achieved within basic dose limits.
- - maximum permissible annual intake of radionuclide through the respiratory system;
- - permissible radionuclide content in the critical organ of the DSA;
- - permissible dose rate of DMDA radiation;
- - permissible flux density of DPPA particles;
- - permissible volumetric activity (concentration) of the radionuclide in the air working area DKA;
- - acceptable contamination of skin, protective clothing and working surfaces of protective equipment.
- - the limit of the annual intake of GGP radionuclide through the respiratory or digestive organs;
- - permissible volumetric activity (concentration) of the DCB radionuclide in atmospheric air and water;
- - permissible dose rate of DMDB;
- - permissible particle flux density DPPB;
- - acceptable contamination of skin, clothing and surfaces of the protective equipment.
Numerical values of permissible levels are contained in full in the “Radiation Safety Standards”.
2Characteristics of the measuring device DKS-101
The universal dosimeter (hereinafter referred to as the dosimeter) is designed for absolute measurements of the absorbed and equivalent dose and absorbed and equivalent dose rate for a wide range of energies of photon and electronic radiation, precision measurement of dose fields of ionizing radiation from medical and industrial devices and apparatus.
The device can be used for dosimetric and physical studies in laboratory and industrial conditions, incl. for verification of dosimetric equipment, certification of X-ray rooms and industrial X-ray and electronic installations, etc.
The dosimeter can be certified as a working standard of the 1st or 2nd category.
The dosimeter operates stably when the ambient temperature changes from +10C to +40C and in conditions of relative humidity up to 80% at a temperature of +30C without moisture condensation, atmospheric pressure from 84 to 106.7 kPa (from 630 to 800 mm Hg. Art.).
It is equipped with ionization chambers, control sources and a water phantom at the customer’s request.
Consists of an electrometric unit with a built-in controlled high-voltage source and a personal computer.
Built-in self-diagnostic systems, a set of mathematical processing functions and logging of measurement results, software in the Windows98 environment provide ease of use and a wide range of service functions.
Technical data
The dosimeter provides the following types of measurements: absorbed dose in water (Gy), equivalent dose (Sv), corresponding dose rate, charge (C), current (A) (current and charge measurement errors are not standardized). The dosimeter has an automatic stop of measurements when the specified dose and time thresholds are reached. Providing measurements of air kerma (Gy), exposure dose (P) and corresponding dose rates can be performed at the customer's request.
Digital resolution, zero stability, high-voltage source voltage range and maximum measurement time of the dosimeter are given in Table 2.1.
Table 2.1
The dosimeter has measurement ranges specified in Table 2.2.
Table 2.2
Dosimeter's own background level.
After the time for establishing the operating mode (without connecting the ionization chamber) no more than 510-15 A.
For 8 hours of continuous operation after the time of establishment of the operating mode (without connecting the ionization chamber) no more than 110-14 A.
From the readings under normal conditions (without connecting the ionization chamber) when the temperature changes in the operating temperature range from +10 to +40C, no more than 210-14 A.
From readings under normal conditions (without connecting an ionization chamber) when the relative air humidity changes to 80% at a temperature of 30 C, no more than 110-14 A.
The instability of the dosimeter readings for 8 hours of continuous operation after the time of establishment of the operating mode is no more than 0.2% in the sensitive range of MTD measurement (the integral of MTD and PD).
The time to establish the readings is no more than:
- 100 s - in the sensitive range;
- 10 s - on other ranges.
The limits of permissible additional measurement error are:
from readings under normal conditions when the temperature changes in the operating temperature range from +10 to +40C when measuring MTD (the integral of MTD and PD) - 0.2%.
from readings under normal conditions when relative air humidity changes to 80% at a temperature of 30C when measuring MTD (the integral of MTD and PD) - 0.2%.
from the readings under normal conditions when working in a constant magnetic field of no more than 400 A/m when measuring MTD (the integral of MTD and PD) - 0.2%.
The dosimeter is powered from a single-phase AC network with a frequency of 50 Hz 1 Hz, harmonic content up to 5% and a rated voltage of 220 V with a permissible deviation from - 15% to +10%.
Power consumed from the network by the electrometric unit, at rated voltage power supply no more than 4 VA.
The insulation between the body of the electrometric unit and the contacts of the power cable plug can withstand the test voltage for 1 minute without breakdown direct current 4000 V. The insulation resistance of the above circuits is at least 20 MOhm under normal conditions.
MTBF not less than 3000 hours.
Average service life is at least 6 years.
Design of the electrometric unit IP30С (according to GOST 14254-96).
Overall dimensions and weight of the installation are given in table. 2.3.
Table 2.3
Type of climatic version of the dosimeter V1 GOST 12997-84.
The dosimeter operates stably when the ambient temperature changes from +10C to 40C and in conditions of relative humidity up to 80% at a temperature of +30C without condensation, atmospheric pressure from 84 to 106.7 kPa (from 630 to 800 mm Hg .).
The electrometric unit has mechanical strength in accordance with the requirements for products of group L1 GOST 12997-84.
(Russian designation: Gr; international: Gy). The previously used non-system unit rad is equal to 0.01 Gy.
Does not reflect the biological effect of radiation (see equivalent dose).
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More about radiation
More about Radiation
Subtitles
Hello. In this episode of the TranslatorsCafe.com channel we will talk about ionizing radiation or radiation. We will look at sources of radiation, ways to measure it, and the effect of radiation on living organisms. We will talk in more detail about such radiation parameters as absorbed dose rate, as well as equivalent and effective doses of ionizing radiation. Radiation has many uses, from generating electricity to treating cancer patients. In this video, we will discuss how radiation affects the tissues and cells of humans, animals, and biomaterials, with a particular focus on how quickly and how severely damage occurs to irradiated cells and tissues. Radiation is a natural phenomenon that manifests itself in the fact that electromagnetic waves or elementary particles with high kinetic energy move within a medium. In this case, the medium can be either matter or vacuum. Radiation is all around us, and our life without it is unthinkable, since the survival of humans and other animals without radiation is impossible. Without radiation on Earth there will be no such natural phenomena as light and heat necessary for life. There would be no cell phones or Internet. In this video we will discuss a special type of radiation, ionizing radiation or radiation, which is all around us. Ionizing radiation has energy sufficient to remove electrons from atoms and molecules, that is, to ionize the irradiated substance. Ionizing radiation in the environment can arise due to either natural or artificial processes. Natural sources of radiation include solar and cosmic radiation, certain minerals such as granite, and radiation from certain radioactive materials such as uranium and even ordinary bananas, which contain the radioactive isotope potassium. Radioactive raw materials are mined in the depths of the earth and used in medicine and industry. Sometimes radioactive materials enter the environment as a result of industrial accidents and in industries that use radioactive raw materials. Most often this occurs due to non-compliance with safety rules for storing and working with radioactive materials or due to the absence of such rules. It is worth noting that until recently, radioactive materials were not considered hazardous to health. On the contrary, they were used as healing drugs, and they were also valued for their beautiful glow. Uranium glass is an example of a radioactive material used for decorative purposes. This glass glows fluorescent green due to the addition of uranium oxide. The percentage of uranium in this glass is relatively small and the amount of radiation it emits is small, so uranium glass is considered relatively safe for health. They even made glasses, plates and other utensils from it. Uranium glass is prized for its unusual glow. The sun emits ultraviolet light, so uranium glass glows in sunlight, although this glow is much more pronounced under ultraviolet light lamps. In radiation, higher energy photons (ultraviolet) are absorbed and lower energy photons (green) are emitted. As you have seen, these beads can be used to test dosimeters. You can buy a bag of beads on eBay.com for a couple of dollars. First let's look at some definitions. There are many ways to measure radiation, depending on what exactly we want to know. For example, one can measure the total amount of radiation in a given location; you can find the amount of radiation that disrupts the functioning of biological tissues and cells; or the amount of radiation absorbed by a body or organism, and so on. Here we will look at two ways to measure radiation. The total amount of radiation in the environment, measured per unit time, is called the total dose rate of ionizing radiation. The amount of radiation absorbed by the body per unit time is called the absorbed dose rate. The absorbed dose rate is found using information about the total dose rate and the parameters of the object, organism, or part of the body that is exposed to radiation. These parameters include mass, density and volume. Absorbed and exposure dose values are similar for materials and tissues that absorb radiation well. However, not all materials are like this, so often the absorbed and exposure doses of radiation differ, since the ability of an object or body to absorb radiation depends on the material from which it is composed. For example, a sheet of lead absorbs gamma radiation much better than an aluminum sheet of the same thickness. We know that a large dose of radiation, called the acute dose, causes health risks, and the higher the dose, the greater the health risk. We also know that radiation affects different cells in the body differently. Cells that undergo frequent division, as well as unspecialized cells, are most affected by radiation. For example, cells in the embryo, blood cells, and cells of the reproductive system are most susceptible to the negative effects of radiation. At the same time, skin, bones, and muscle tissue are less susceptible to radiation. But radiation has the least effect on nerve cells. Therefore, in some cases, the overall destructive effect of radiation on cells that are less exposed to radiation is less, even if they are exposed to more radiation, than on cells that are more exposed to radiation. According to the theory of radiation hormesis, small doses of radiation, on the contrary, stimulate the body's defense mechanisms, and as a result the body becomes stronger and less susceptible to disease. It should be noted that these studies are at an early stage, and it is not yet known whether such results will be obtained outside the laboratory. Now these experiments are carried out on animals and it is unknown whether these processes occur in the human body. Due to ethical considerations, it is difficult to obtain permission for such research involving human participants. Absorbed dose is the ratio of the energy of ionizing radiation absorbed in a given volume of a substance to the mass of the substance in this volume. Absorbed dose is the main dosimetric quantity and is measured in joules per kilogram. This unit is called gray. Previously, the non-systemic unit rad was used. The absorbed dose depends not only on the radiation itself, but also on the material that absorbs it: the absorbed dose of soft X-rays in bone tissue can be four times the absorbed dose in air. At the same time, in a vacuum the absorbed dose is zero. The equivalent dose, which characterizes the biological effect of irradiation of the human body with ionizing radiation, is measured in sieverts. To understand the difference between dose and dose rate, we can draw an analogy with a kettle into which water is poured from the tap. The volume of water in the kettle is the dose, and the filling speed, depending on the thickness of the water stream, is the dose rate, that is, the increment in the radiation dose per unit time. Equivalent dose rate is measured in sieverts per unit of time, for example microsieverts per hour or millisieverts per year. Radiation is generally invisible to the naked eye, so special measuring instruments are used to determine the presence of radiation. One widely used device is a dosimeter based on a Geiger-Muller counter. The counter consists of a tube in which the number of radioactive particles is counted, and a display that displays the number of these particles in different units, most often as the amount of radiation over a certain period of time, for example per hour. Instruments with Geiger counters often produce short beeps, such as clicks, each of which indicates that a new emitted particle or particles have been counted. This sound can usually be turned off. Some dosimeters allow you to select the click frequency. For example, you can set the dosimeter to make a sound only after every twentieth particle counted or less often. In addition to Geiger counters, dosimeters also use other sensors, such as scintillation counters, which make it possible to better determine what type of radiation currently predominates in the environment. Scintillation counters are good at detecting both alpha, beta and gamma radiation. These counters convert the energy released during radiation into light, which is then converted in a photomultiplier into an electrical signal, which is measured. During measurements, these counters work over a larger surface area than Geiger counters, so they measure more efficiently. Ionizing radiation has very high energy and therefore ionizes the atoms and molecules of biological material. As a result, electrons are separated from them, which leads to a change in their structure. These changes are caused by ionization weakening or breaking the chemical bonds between particles. This damages molecules inside cells and tissues and disrupts their function. In some cases, ionization promotes the formation of new bonds. The disruption of cell function depends on how much radiation damages their structure. In some cases, disorders do not affect cell function. Sometimes the work of cells is disrupted, but the damage is minor and the body gradually restores the cells to working condition. Such disturbances often occur during the normal functioning of cells, and the cells themselves return to normal. Therefore, if the level of radiation is low and the damage is minor, then it is quite possible to restore the cells to their normal state. If the radiation level is high, then irreversible changes occur in the cells. With irreversible changes, cells either do not work as they should or stop working altogether and die. Damage by radiation to vital and essential cells and molecules, such as DNA and RNA molecules, proteins or enzymes, causes radiation sickness. Damage to cells can also cause mutations, which can cause the children of patients whose cells are affected to develop genetic diseases. The mutations can also cause cells in patients' bodies to divide too quickly - which in turn increases the likelihood of cancer. Today, our knowledge about the effects of radiation on the body and the conditions under which this effect is aggravated is limited, since researchers have very little material at their disposal. Much of our knowledge is based on research into the medical records of victims of the atomic bombings of Hiroshima and Nagasaki, as well as victims of the Chernobyl nuclear power plant explosion. It is also worth noting that some studies of the effects of radiation on the body, which were carried out in the 50s - 70s. last century, were unethical and even inhumane. In particular, these are studies conducted by the military in the United States and the Soviet Union. Most of these experiments were conducted at test sites and designated areas for testing nuclear weapons, such as the Nevada Test Site in the United States, the Soviet Nuclear Test Site on Novaya Zemlya, and the Semipalatinsk Test Site in what is now Kazakhstan. In some cases, experiments were carried out during military exercises, such as during the Totsk military exercises (USSR, in what is now Russia) and during the Desert Rock military exercises in Nevada, USA. During these exercises, researchers, if you can call them that, studied the effects of radiation on the human body after atomic explosions. From 1946 to the 1960s, experiments on the effects of radiation on the body were also carried out in some American hospitals without the knowledge or consent of the patients. Thank you for your attention! If you liked this video, please don't forget to subscribe to our channel!