Topic: Detection and measurement of ionizing radiation. Basic methods for measuring radioactivity Correlation between radiation levels and land pollution
Photoelectric effect Compton effect Pair formation
2. At Compton scattering The gamma quantum transfers part of its energy to one of the outer electrons of the atom. This recoil electron, acquiring significant kinetic energy, spends it on the ionization of the substance (this is already secondary ionization, since the g-quantum, having knocked out the electron, has already produced primary ionization).
The g-quantum after a collision loses a significant part of its energy and changes its direction of movement, i.e. dissipates.
The Compton effect is observed in a wide range of gamma ray energies (0.02-20 MeV).
3. Formation of steam. Gamma rays passing near the atomic nucleus and having an energy of at least 1.02 MeV are converted into two particles, an electron and a positron, under the influence of the field of the atomic nucleus. Part of the energy of a gamma quantum is converted into the equivalent mass of two particles (according to Einstein’s relation E=2me*C²= 1.02 MeV). The remaining energy of the gamma quantum is transferred to the resulting electron and positron in the form of kinetic energy. The resulting electron ionizes atoms and molecules, and the positron annihilates with any of the electrons of the medium, forming two new gamma quanta with an energy of 0.51 MeV each. Secondary gamma quanta spend their energy on the Compton effect and then on the photoelectric effect. The higher the energy of gamma rays and the density of the substance, the more likely the process of pair formation. Therefore, heavy metals, such as lead, are used to protect against gamma rays.
X-rays interact with matter in a similar way due to these same three effects.
- Characteristic and bremsstrahlung X-ray radiation. Differences and similarities between X-rays and gamma radiation. Law of gamma radiation attenuation.
Characteristic bremsstrahlung arises as a result of the excitation of an atom, when electrons that have transferred to the outer orbit return to the orbit closest to the nucleus and give off excess energy in the form of characteristic X-ray radiation (its frequency is characteristic of each chemical element). X-ray machines use characteristic x-ray radiation. When beta particles (electrons) interact with a substance, in addition to the ionization of the atoms of this substance, the beta particles (electrons), interacting with the positive charge of the nuclei, bend their trajectory (decelerate) and at the same time lose their energy in the form of bremsstrahlung X-rays.
Gamma rays are emitted from the nuclei of p/a isotopes during their decay, and X-rays arise during electron transitions within the electron shells of an atom. The frequency of gamma rays is higher than the frequency of X-rays, and the penetrating power in matter and interaction effects are approximately the same.
The thicker the absorber layer, the more the gamma ray flux passing through it will be weakened.
For each material, a half-attenuation layer D1/2 was experimentally established (this is the thickness of any material that attenuates gamma radiation by half.)
It is equal for air -190m, wood -25cm, biological tissue -23cm, soil -14cm, concrete -10cm, steel -3cm, lead -2cm. (D1/2 » r /23)
Reasoning in the same way as when deriving the law of p/a decay, we obtain:
D/D1/2 -D/D1/2 - 0.693D/D1/2
I = Iо / 2 or I = Iо * 2(another type of notation I = Iоe)
where: I is the intensity of gamma rays after passing through an absorber layer of thickness D;
Iо - initial intensity of gamma rays.
10. Problems of dosimetry and radiometry. External and internal irradiation of the body. The relationship between activity and dose generated by their gamma radiation. Methods of protection from local radiation sources .
Dosimetry- this is a quantitative and qualitative determination of quantities characterizing the effects of ionizing radiation on matter using various physical methods and the use of special equipment.
Radiometry- develops the theory and practice of measuring radioactivity and identifying radioisotopes.
The biological effect of X-ray and nuclear radiation on the body is due to the ionization and excitation of atoms and molecules of the biological environment.
A ¾¾¾® B.object
b ¾¾¾® Ionization
G ¾¾¾® is proportional to ¾¾¾®g
n ¾¾¾® absorbed energy ¾¾¾® n
r ¾¾¾® radiation ¾¾¾® r (x-ray radiation)
Radiation dose is the amount of ionizing radiation energy absorbed per unit volume (mass) of the irradiated substance.
Irradiation from external radiation sources is called external irradiation. Irradiation from radioactive substances that enter the body with air, water, and food creates internal radiation.
Using the Kg value (the gamma constant value is given in reference books for all p/a isotopes), you can determine the dose rate of a point source of any isotope.
P = Kg A / R²,Where
R - exposure dose rate, R/h
Kg - ionization constant of the isotope, R/h cm² / mKu
A - activity, mKu
R - distance, cm.
You can protect yourself from local sources of radioactive radiation by shielding, increasing the distance to the source and reducing the time of its exposure to the body.
11. Dose and dose rate. Units of measurement of exposure, absorbed, equivalent, effective dose.
Radiation dose is the amount of ionizing radiation energy absorbed per unit volume (mass) of the irradiated substance. In the literature, documents of the ICRP (International Commission on Radiation Protection), NCRP (National Committee of Russia) and SCEAR (Scientific Committee on the Effects of Atomic Radiation at the United Nations), the following concepts are distinguished:
- Exposure dose (ionizing power of x-rays and gamma rays in air) in roentgens; X-ray (P) - exposure dose of X-ray or g-radiation (i.e. photon radiation), creating two billion ion pairs in 1 cm³ of air. (X-rays measure the exposure of the source, the radiation field, as radiologists say, incident radiation).
- Absorbed dose - the energy of ionizing radiation absorbed by the tissues of the body in terms of unit mass in Rads and Grays;
Glad (radiation absorbent dose - English) - the absorbed dose of any type of ionizing radiation, at which energy equal to 100 erg is absorbed in 1 g of mass of a substance. (In 1 g of biological tissue of different composition, different amounts of energy are absorbed.)
Dose in rads = dose in roentgens multiplied by k-t, reflecting the radiation energy and the type of absorbing tissue. For air: 1 rad = 0.88 roentgen;
for water and soft tissues 1rad = 0.93R (in practice they take 1rad = 1R)
for bone tissue 1rad = (2-5)P
The unit adopted in the C system is Gray (1 kg of mass absorbs 1 J of radiation energy). 1Gy=100 rad (100R)
- Equivalent dose - absorbed dose multiplied by a coefficient reflecting the ability of a given type of radiation to damage body tissue in Rem and Sievert. BER (biological equivalent of an X-ray) is a dose of any nuclear radiation at which the same biological effect is created in a biological environment as with a dose of X-ray or gamma radiation of 1 roentgen. D in rem = D in roentgen*RBE. RBE - coefficient of relative biological effectiveness or quality coefficient (QC)
For b, g and roentgen. radiation RBE (KK) = 1; for a and protons = 10;
slow neutrons = 3-5; fast neutrons = 10.
Sievert(Sv) is an equivalent dose of any type of radiation absorbed in 1 kg of biological tissue, creating the same biological effect as the absorbed dose of 1 Gy of photon radiation. 1 Sv = 100 rem(u = 100R)
-Effective equivalent dose - equivalent dose multiplied by a coefficient taking into account the different sensitivity of different tissues to radiation, in Sieverts.
Radiation risk coefficients for different human tissues (organs), recommended by the ICRP: (for example, 0.12 - red bone marrow, 0.15 - mammary gland, 0.25 - testes or ovaries;) The coefficient shows the share per individual organ with uniform irradiation of the whole body
In biological terms, it is important to know not just the radiation dose received by an object, but the dose received per unit time.
Dose rate is the radiation dose per unit time.
D = P / t For example, R/h, mR/h, μR/h, μSv/h, mrem/min, Gy/s, etc.
The absorbed dose rate is spoken of as the dose increment per unit time.
12 Characteristics of a-, d-particles and g-radiation.
We will consider the properties of different types of ionizing radiation in the form of a table.
| Type of radiation | What does it represent? | Charge | Weight | Energy MeV | Speed | Ionization in air at 1 cm path | Mileage...in: Air Biological. Metal Fabrics | ||
| a | Flow of helium nuclei | Two emails Positive charge ÅÅ | 4th | 2 – 11 | 10-20 thousand km/h | 100-150 thousand ion pairs | 2 – 10 cm | Fractions of mm (~0.1mm) | Hundredths of Mm |
| b | Electron Flow | Elementary neg. Charge(-) | 0.000548 am | 0 – 12 | 0.3-0.99 speed of light (C) | 50-100 ion pairs | Up to 25 meters | Up to 1 cm | A few mm. |
| g | El-instant Radiation l<10 -11 м (в.свет 10 -7 м) | Doesn't have | g-quantum has rest mass =0 | From keV to several MeV | From 300,000 km/sec | Weak | 100-150 meters | meters | Tens of cm. |
13. Characteristics of radioactive contamination during a nuclear power plant accident.
Iodine-131 Strontium - 90(Sr-90) - T 1/2 -28 years and Cesium - 137
Zoning after the accident (based on soil contamination with Cs-137 and annual dose):
Exclusion zone (relocation) - more than 40 Ci/km² (dose more than 50 mSv/year);
Relocation zone (voluntary) – from 15 to 40 Ci/km². (dose 20 - 50 mSv/year);
Restricted residence zone (with temporary resettlement of pregnant women and children) 5 - 15 Ci/km². (dose from 5 to 20 mSv/year);
Radiation control zone (residence zone with preferential socio-economic status) 1-5 Ci/km² (dose from 1 to 5 mSv/year).
In the Russian Federation, 15 regions (Bryansk, Kursk, Kaluga, Tula, Oryol, Ryazan, etc. - from 1 to 43% of the territory) received partial radioactive contamination (more than 1 Ci/km2) from the Chernobyl accident.
According to the legislation of the Russian Federation, the population living on lands with contamination (cesium) of more than 1 Ci/km² has the right to minimal benefits
14. Detectors of ionizing radiation. Classification. The principle and scheme of operation of the ionization chamber.
ionization chambers;
- proportional counters;
Schematic diagram of the operation of an ionization detector.
This chamber is filled with air or an inert gas, in which two electrodes (cathode and anode) are located, creating an electric field.
Dry air or gas are good insulators and do not conduct electricity. But charged alpha and beta particles, having entered the chamber, ionize the gaseous medium, and gamma quanta first form fast electrons (photoelectrons, Compton electrons, electron-positron pairs) in the walls of the chamber, which also ionize the gaseous medium. The resulting positive ions move to the cathode, negative ions to the anode. An ionization current appears in the circuit, proportional to the amount of radiation.
The ionization current for the same amount of ionizing radiation depends in a complex way on the voltage applied to the electrodes of the chamber. This dependency is called current-voltage characteristic of the ionization detector.
Ionization chamber used to measure all types of nuclear radiation. Structurally, they are designed as flat, cylindrical, spherical, or thimble-shaped with a volume from fractions of cm³ to 5 liters. Usually filled with air. The chamber material is plexiglass, bakelite, polystyrene, maybe aluminum. Widely used in individual dosimeters (DK-0.2; KID-1, KID-2, DP-22V, DP-24, etc.).
15. Characteristics of radioactive contamination during a nuclear explosion.
During a fission chain reaction, U-235 and Pu-239 in an atomic bomb, about 200 radioactive isotopes of approximately 35 chemical elements are formed. During a nuclear explosion, a fission chain reaction occurs instantly throughout the entire mass of the fissile substance, and the resulting radioactive isotopes are released into the atmosphere, and then fall out on the ground in the form of an extended radioactive trail.
The entire area of radioactive contamination of the area, according to the degree of contamination, is divided into 4 zones, the boundaries of which are characterized by: radiation doses during complete decay
– D ∞ in Roentgens and radiation levels 1 hour after the explosion P 1 in R/h. 
 |
Rice. 2.1. Radioactive contamination zones during a nuclear explosion
Names of zones (in parentheses the values P 1 (R/h), D ∞ (P)): A – moderate infection(8 R/h, 40 R), B – strong(80 R/h, 400 R), B – dangerous(240 R/h, 1200 R), G - extremely dangerous infection(800 R/h, 4000 R).
The reference books show the sizes of the zones depending on the power of the explosion and wind speed in the upper layers of the atmosphere - the length and width of each zone are indicated in km. In general, an area is considered contaminated if the radiation level is 0.5 R/h - in wartime and 0.1mR/h in peacetime (natural background radiation in Yaroslavl - 0.01 mR/h,)
Due to the decay of radioactive substances, there is a constant decrease in the level of radiation, according to the ratio
Р t = Р 1 t – 1.2
R
Rice. 2.2. Reducing the level of radiation in the wake of a nuclear explosion
Graphically, this is a steeply falling exponential. Analysis of this ratio shows that with a sevenfold increase in time, the radiation level decreases by 10 times. The decline in radiation after the Chernobyl accident was much slower
For all possible situations, radiation levels and doses are calculated and tabulated.
For agricultural production, radioactive contamination of the area poses the greatest danger, because people, animals and plants are exposed not only to external gamma irradiation, but also internally when radioactive substances enter the body with air, water and food. In unprotected people and animals, depending on the dose received, radiation sickness may occur, and agricultural plants slow down their growth, reduce the yield and quality of crop products, and in case of severe damage, plant death occurs.
16. Basic methods of measuring radioactivity (absolute, calculated and relative (comparative) Meter efficiency. Counting (operating) characteristic.
The radioactivity of drugs can be determined by the absolute, calculated and relative (comparative) method. The latter is the most common.
Absolute method. A thin layer of the material under study is applied to a special thin film (10-15 μg/cm²) and placed inside the detector, as a result of which the full solid angle (4p) is used to register emitted beta particles, for example, and almost 100% counting efficiency is achieved. When working with a 4p counter, you do not need to introduce numerous corrections, as with the calculation method.
The activity of the drug is expressed immediately in units of activity Bq, Ku, mKu, etc.
By calculation method determine the absolute activity of alpha and beta emitting isotopes using conventional gas-discharge or scintillation counters.
A number of correction factors are introduced into the formula for determining the activity of a sample, taking into account radiation losses during measurement.
A = N/w×e×k×r×q×r×g m×2.22×10¹²
A- activity of the drug in Ku;
N- counting rate in imp/min minus background;
w- correction for geometric measurement conditions (solid angle);
e- correction for the resolving time of the counting installation;
k- correction for absorption of radiation in the air layer and in the window (or wall) of the counter;
r- correction for self-absorption in the drug layer;
q- correction for backscattering from the substrate;
r- correction for the decay scheme;
g- correction for gamma radiation with mixed beta and gamma radiation;
m- weighed portion of the measuring drug in mg;
2.22×10¹² - conversion factor from the number of disintegrations per minute to Ci (1 Ci = 2.22*10¹² disintegration/min).
To determine the specific activity, it is necessary to convert the activity per 1 mg to 1 kg .
Aud = A*10 6, (Ku/kg)
Preparations for radiometry can be prepared thin, thick or intermediate layer the material being studied.
If the material being tested has half attenuation layer - D1/2,
That thin
- at d<0,1D1/2, intermediate
- 0.1D1/2
All correction factors themselves, in turn, depend on many factors and, in turn, are calculated using complex formulas. Therefore, the calculation method is very labor-intensive.
Relative (comparative) method has found wide application in determining the beta activity of drugs. It is based on comparing the counting rate from a standard (a drug with known activity) with the counting rate of the measured drug.
In this case, there must be completely identical conditions when measuring the activity of the standard and the test drug.
Apr = Aet* Npr/Net, Where
Aet is the activity of the reference drug, dispersion/min;
Apr - radioactivity of the drug (sample), dispersion/min;
Net - counting speed from the standard, imp/min;
Npr - counting rate from the drug (sample), imp/min.
The passports for radiometric and dosimetric equipment usually indicate with what error the measurements are made. Maximum relative error measurements (sometimes called the basic relative error) is indicated as a percentage, for example, ± 25%. For different types of instruments it can be from ± 10% to ± 90% (sometimes the error of the type of measurement for different sections of the scale is indicated separately).
From the maximum relative error ± d% you can determine the maximum absolute measurement error. If readings from instrument A are taken, then the absolute error is DA=±Ad/100. (If A = 20 mR, and d = ±25%, then in reality A = (20 ± 5) mR. That is, in the range from 15 to 25 mR.
17. Detectors of ionizing radiation. Classification. Principle and operating diagram of a scintillation detector.
Radioactive radiation can be detected (isolated, detected) using special devices - detectors, the operation of which is based on the physical and chemical effects that arise when radiation interacts with matter.
Types of detectors: ionization, scintillation, photographic, chemical, calorimetric, semiconductor, etc.
The most widely used detectors are based on measuring the direct effect of the interaction of radiation with matter - ionization of the gaseous medium. These are: - ionization chambers;
- proportional counters;
- Geiger-Muller counters (gas-discharge counters);
- corona and spark counters,
as well as scintillation detectors.
Scintillation (luminescent) The radiation detection method is based on the property of scintillators to emit visible light radiation (light flashes - scintillations) under the influence of charged particles, which are converted by a photomultiplier into electric current pulses.
Cathode Dynodes Anode The scintillation counter consists of a scintillator and
PMT. Scintillators can be organic and
Inorganic, in solid, liquid or gas
Condition. This is lithium iodide, zinc sulfide,
Sodium iodide, angracene single crystals, etc.
100 +200 +400 +500 volts
PMT operation:- Under the influence of nuclear particles and gamma quanta
In the scintillator, atoms are excited and emit quanta of visible color - photons.
Photons bombard the cathode and knock photoelectrons out of it:
Photoelectrons are accelerated by the electric field of the first dynode, knock out secondary electrons from it, which are accelerated by the field of the second dynode, etc., until an avalanche flow of electrons is formed that hits the cathode and is recorded by the electronic circuit of the device. The counting efficiency of scintillation counters reaches 100%. The resolution is much higher than in ionization chambers (10 v-5 - !0 v-8 versus 10¯³ in ionization chambers). Scintillation counters find very wide application in radiometric equipment
18. Radiometers, purpose, classification.
By appointment.
Radiometers - devices intended for:
Measurements of the activity of radioactive drugs and radiation sources;
Determination of flux density or intensity of ionizing particles and quanta;
Surface radioactivity of objects;
Specific activity of gases, liquids, solids and granular substances.
Radiometers mainly use gas-discharge counters and scintillation detectors.
They are divided into portable and stationary.
As a rule, they consist of: - a detector-pulse sensor; - pulse amplifier; - converting device; - electromechanical or electronic numerator; - high voltage source for the detector; - power supply for all equipment.
In order of improvement, the following were produced: radiometers B-2, B-3, B-4;
dekatron radiometers PP-8, RPS-2; automated laboratories “Gamma-1”, “Gamma-2”, “Beta-2”; equipped with computers that allow the calculation of up to several thousand sample samples with automatic printing of results. DP-100 installations, KRK-1, SRP-68 radiometers are widely used -01.
Indicate the purpose and characteristics of one of the devices.
19. Dosimeters, purpose, classification.
The industry produces a large number of types of radiometric and dosimetric equipment, which can be classified:
By the method of recording radiation (ionization, scintillation, etc.);
By type of detected radiation (a,b,g,n,p)
Power source (mains, battery);
By place of application (stationary, field, individual);
By appointment.
Dosimeters - devices that measure exposure and absorbed dose (or dose rate) of radiation. Basically consist of a detector, an amplifier and a measuring device. The detector can be an ionization chamber, a gas-discharge counter or a scintillation counter.
Divided into dose rate meters- these are DP-5B, DP-5V, IMD-5, and individual dosimeters- measure the radiation dose over a period of time. These are DP-22V, ID-1, KID-1, KID-2, etc. They are pocket dosimeters, some of them are direct-reading.
There are spectrometric analyzers (AI-Z, AI-5, AI-100) that allow you to automatically determine the radioisotope composition of any samples (for example, soils).
There are also a large number of alarms indicating excess background radiation and the degree of surface contamination. For example, SZB-03 and SZB-04 signal that the amount of hand contamination with beta-active substances is exceeded.
Indicate the purpose and characteristics of one of the devices
20. Equipment for the radiological department of the veterinary laboratory. Characteristics and operation of the SRP-68-01 radiometer.
Staff equipment for radiological departments of regional veterinary laboratories and special district or inter-district radiological groups (at regional veterinary laboratories)
Radiometer DP-100
Radiometer KRK-1 (RKB-4-1em)
Radiometer SRP 68-01
Radiometer “Besklet”
Radiometer - dosimeter -01Р
Radiometer DP-5V (IMD-5)
Set of dosimeters DP-22V (DP-24V).
Laboratories can be equipped with other types of radiometric equipment.
Most of the above radiometers and dosimeters are available at the department in the laboratory.
21. Periodization of hazards during a nuclear power plant accident.
Nuclear reactors use intranuclear energy released during fission chain reactions of U-235 and Pu-239. During a fission chain reaction, both in a nuclear reactor and in an atomic bomb, about 200 radioactive isotopes of about 35 chemical elements are formed. In a nuclear reactor, the chain reaction is controlled, and nuclear fuel (U-235) “burns out” in it gradually over 2 years. Fission products - radioactive isotopes - accumulate in the fuel element (fuel element). An atomic explosion cannot occur in a reactor either theoretically or practically. At the Chernobyl nuclear power plant, as a result of personnel errors and a gross violation of technology, a thermal explosion occurred, and radioactive isotopes were released into the atmosphere for two weeks, carried by winds in different directions and, settling over vast areas, creating spotty pollution of the area. Of all the r/a isotopes, the most biologically hazardous were: Iodine-131(I-131) – with a half-life (T 1/2) 8 days, Strontium - 90(Sr-90) - T 1/2 -28 years and Cesium - 137(Cs-137) - T 1/2 -30 years. As a result of the accident, 5% of the fuel and accumulated radioactive isotopes were released at the Chernobyl nuclear power plant - 50 MCi of activity. For cesium-137, this is equivalent to 100 pieces. 200 Kt. atomic bombs. Now there are more than 500 reactors in the world, and a number of countries provide 70-80% of their electricity from nuclear power plants, in Russia 15%. Taking into account the depletion of organic fuel reserves in the foreseeable future, the main source of energy will be nuclear.
Periodization of hazards after the Chernobyl accident:
1. period of acute iodine danger (iodine - 131) for 2-3 months;
2. period of surface contamination (short- and medium-lived radionuclides) - until the end of 1986;
3. period of root entry (Cs-137, Sr-90) - from 1987 for 90-100 years.
22. Natural sources of ionizing radiation. Cosmic radiation and natural radioactive substances. Dose from ERF.
1. Natural sources of ionizing radiation (iii)
Natural background radiation consists of:
Cosmic radiation;
Radiation from natural radioactive substances found in earth
rocks, water, air, building materials;
Radiation from natural radioactive substances contained in plants
and the animal world (including humans).
Cosmic radiation - divided by primary this is a continuously falling stream of hydrogen nuclei (protons) - 80% and nuclei of light elements (helium (alpha particles), lithium, beryllium, boron, carbon, nitrogen) - 20%, evaporating from the surfaces of stars, nebulae and the sun and amplified (accelerated ) repeatedly in the electromagnetic fields of space objects up to an energy of the order of 10 10 eV and higher. (In our galaxy - Milky Way - 300 billion stars, and galaxies 10 14)
Interacting with the atoms of the air shell of the earth, this primary cosmic radiation gives birth to streams secondary cosmic radiation, which is the largest of all known elementary particles and radiations (± mu and pi mesons - 70%; electrons and positrons - 26%, primary protons - 0.05%, gamma quanta, fast and ultrafast neutrons).
Natural radioactive substances divided into three groups:
1) Uranium and thorium with their decay products, as well as potassium-40 and rubidium-87;
2) Less common isotopes and isotopes with a large T 1/2 (calcium-48, zirconium-96, neodymium-150, samarium-152, rhenium-187, bismuth-209, etc.);
3) Carbon-14, tritium, beryllium -7 and -9 - continuously formed in the atmosphere under the influence of cosmic radiation.
The most common in the earth's crust is rubidium-87 (T 1/2 = 6.5.10 10 years), then uranium-238, thorium-232, potassium-40. But the radioactivity of potassium-40 in the earth’s crust exceeds the radioactivity of all other isotopes combined (T 1/2 = 1.3 10 9 years). Potassium-40 is widely dispersed in soils, especially in clayey ones, its specific activity is 6.8.10 -6 Ci/g.
In nature, potassium consists of 3 isotopes: stable K-39 (93%) and K-41 (7%) and radioactive K-40 (01%). The concentration of K-40 in soils is 3-20 nKu/g (pico - 10 -12),
The world average is taken to be 10. Hence, in 1 m³ (2 tons) - 20 µKu, in 1 km² - 5Ku (root layer = 25 cm). The average content of U-238 and Th-232 is taken to be 0.7 nKu/g. These three isotopes create the dose rate of the natural background from the soil = approximately 5 μR/h (and the same amount from cosmic radiation) Our background (8-10 μR/h below average. Fluctuations across the country 5-18, in the world up to 130 and even up to 7000 microR/h..
Construction Materials create additional gamma radiation inside buildings (in reinforced concrete up to 170 mrad/year, in wooden ones - 50 mrad/year).
Water, Being a solvent, it contains soluble complex compounds of uranium, thorium, and radium. In seas and lakes the concentration of radioactive elements is higher than in rivers. Mineral springs contain a lot of radium (7.5*10 -9 Cu/l) and radon (2.6*10 -8 Cu/l). Potassium-40 in the waters of rivers and lakes is approximately the same as radium (10 -11 Cu/l).
Air(atmosphere) contains radon and thoron released from the earth's rocks and carbon-14 and tritium continuously formed in the atmosphere under the influence of neutrons of secondary cosmic radiation interacting with nitrogen and hydrogen of the atmosphere. The accumulation of radon in poorly ventilated buildings is especially dangerous. A standard has been adopted in newly constructed buildings £100 Bq/m³, in occupied buildings £200 Bq/m³, if 400 Bq/m³ is exceeded, measures are taken to reduce radon or the use of the building is repurposed. Calculations show that with radon concentrations of 16 and 100 Bq/m³, the annual dose will be 100 mrem and 1 rem, respectively. Real concentration"11 Bq/m³
Plants and animals very intensively absorb radioactive isotopes K-40, C-14, H-3 from the environment (these are the building blocks of protein molecules). Other radionuclides to a lesser extent.
Internal irradiation of most organs is due to the presence of K-40 in them. The annual dose from K-40 will be: for red bone marrow - 27 mrad
Lungs - 17 mrad
Gonads -15 mrad
From other radionuclides in the body, the dose will be 1/100, 1/1000 of these values. The exception is radon, which enters the lungs by inhalation and creates a dose of up to 40 mrad per year.
Thus, only from natural and due to external and internal irradiation a person receives an annual dose of 200 mrad (mrem) (or 2mSv)
from iii Earthly passage.- 167 (internal exposure from K-40 and Rn-222......... 132 mrem)
(external irradiation from K-40, U-238, Th-232, Rb-87........... 35 mrem)
from iii Cosmic origin .- 32 (external irradiation from g-quanta, m, p-mesons.... .30mrem)
(internal irradiation from S-14, N-3................. 2 mrem)
conclusions.1. The dose from external exposure to natural radiation is 65 mrem, which is 30% of the total dose. We measure only this part of the dose with dosimeters.
2. The contribution of radon to the annual dose is 25-40%.
Smokers receive an additional dose of radiation to the lungs from radioactive Po-210 (in one cigarette there is 7mBq Po). According to US statistics, mortality from smoking is higher than from alcohol - 150,000 hours / year.
For the last millennia, the radiation situation on earth has been stable. Under the conditions of this radiation background, the evolution of flora and fauna took place, and all previous generations of people lived.
24. Artificial sources of ionizing radiation (X-ray installations, nuclear test explosions, nuclear energy, modern technical devices).
Artificial radiation sources create an additional dose load on humans and are divided into four large groups.
1) X-ray machines used in medicine for diagnostic and therapeutic purposes.
2) Nuclear test explosions.
3) Nuclear energy (nuclear fuel cycle enterprises - NFC).
4) A number of modern technical devices (luminous watch dials and measuring instruments, televisions, computer displays, X-ray and gamma installations for flaw detection, viewing things at airports, computed tomography, etc.).
According to ICDAR, if we take the annual equivalent dose from natural radiation sources (200 mrem) as 100%, then artificial ones will additionally account for:
Irradiation from X-ray machines - 20% (40 mrem); (per average person)
Test poisons. explosions from 7% in the early 60s. up to 0.8% in the 80s (declining trend);
Nuclear energy from 0.001% of the natural background in 1965 to 0.05% in 2000 (small growth trend);
For technical devices (TV, computers, etc.) - negligible values.
X-ray installations - by order of the Ministry of Health, doses are determined for
· fluorography of the chest organs up to 0.6 mSv (tooth image 0.1-0.2 mrem)
· fluoroscopy of the lungs up to 1.4 mSv, stomach up to 3.4 mSv (340 mrem)
Nuclear test explosions
From 1945 to 1962, 423 test explosions were carried out in the atmosphere with a total power of more than 500 Mt (USSR, USA, France, China, Great Britain). Underground tests are still being carried out.
During a nuclear explosion, a chain reaction of fission of nuclei of heavy elements (U 235, Pu 239) occurs under the influence of neutrons. During the reaction, about 250 isotopes of 35 x are formed. elements, of which 225 are radioactive. (Example - cutting a watermelon with 235 seeds) The resulting radionuclides have different half-lives - fractions of a second, seconds, minutes, hours, days, months, years, centuries, millennia and millions of years.
Of this large number of nuclear fragments and their daughter products, 10 radionuclides are of interest for veterinary radiobiology and radioecology of farm animals due to their radiotoxicological and physical characteristics.
Most radionuclides are beta and gamma emitters. Iodine-131, barium-140, strontium-89 are especially dangerous in the first months. Subsequently, strontium-90 and caesnium-137.
Over the 35 years after the cessation of nuclear weapons testing, all the products of nuclear explosions fell from the reservoir of the atmosphere and stratosphere onto the surface of mainly the Northern Hemisphere of the Earth, raising the contamination of land with Sr-90 and Cs-137 to 0.2 Ku/km², now it has dropped to 0.1 Ku/km². (for humans - orally)
Nuclear power - these are interconnected nuclear fuel cycle enterprises (mining, enrichment and processing of uranium ore, production of fuel rods, burning them at nuclear power plants, processing of fuel rods, disposal of waste, dismantling of spent nuclear power plants).
Despite the radiation and environmental hazards of nuclear power plants, their number is increasing from year to year. There are more than 500 power reactors in operation around the world, with a total capacity of about 30 thousand MW. They provide 17% of global energy consumption.
Nuclear energy is the most environmentally friendly of all existing methods of generating electricity (with trouble-free operation). A coal plant pollutes the environment with radiation several times more than a nuclear power plant of the same power.
But a number of accidents in recent decades at nuclear power plants, incl. the largest at the Chernobyl Nuclear Power Plant - 04/26/86, leads to severe radioactive contamination of large areas.
The most biologically hazardous isotopes were iodine-131, otrontium-90 and chii-137.
25. Patterns of movement of radioactive substances in the biosphere. Strontium units.
Radioactive substances from nuclear explosions, emergency emissions from nuclear fuel cycle enterprises, radioactive waste not buried in the established manner are included in the components of the biosphere - abiotic (soil, water, air) and biotic (flora, fauna) and take part in the biological cycle of substances.
The shortest route of radioactive substances to humans, excluding direct entry from the atmosphere, is through agricultural means. plants and animals in chains: soil - plant - human; soil - plant - animal - human. During the Chernobyl accident, 50 MCu of activity was released into the atmosphere. Of these, 20% is iodine-131 and 15% isotopes of cesium and up to 2% strontium.
Iodine, entering the body of humans and animals, concentrated in the greatest quantity (from 20 to 60%) in the thyroid gland, disrupting its functions
Moving from one object of the biosphere to another, cesium and strontium behave similarly to potassium and calcium (since they are their analogues in physical properties), ultimately entering the body of animals and humans, reaching maximum concentration in organs physiologically rich in these elements (cesium in muscles, strontium in bones, shells).
There is a certain proportionality of this accumulation per 1 gram of calcium or potassium, expressed in strontium units (SU).
1CE = 1 nCu Sr-90 per 1 gram of Ca (nano = 10 -9)
The ratio of the number of CE of the subsequent link of a biological system to the previous one is called discrimination coefficient (CD) Sr-90 relative to calcium.
CD = CE in forage sample / CE in soil.
Many more issues of transition in the links of biological chains are poorly studied.
26. Toxicity of radioactive isotopes.
Radioactive isotopes of any chemical element, when they enter the body, participate in metabolism in the same way as stable isotopes of a given element. The toxicity of radionuclides is due to:
· type and energy of radiation (the main characteristic determining toxicity),
· half-life;
· physical and chemical properties of the substance in which the radionuclide entered the body;
· type of distribution among tissues and organs;
· rate of excretion from the body.
The concept of LET was introduced - linear energy transfer (this is the amount of energy (in keV) transferred by a particle or quantum to a substance per unit path (in microns)). LET - characterizes specific ionization and is associated with RBE (relative biological effectiveness) of a particular type of radiation. (This was mentioned earlier in lectures)
Radionuclides with very short (fractions of a second) and very long (millions of years) half-lives cannot create an effective dose in the body and therefore cause great harm.
The most dangerous isotopes have a half-life from several days to several tens of years.
In descending order of radiation hazard, radionuclides are divided into 4 radiotoxicity groups (according to NRB - radiation hazard groups).
| Radiotoxicity group | Radionuclide | Average annual permissible concentration in water, K u/l |
| A - especially high radiotoxicity (r/t) | Pb-210, Po-210, Ra-226, Th-230, etc. | 10 -8 - 10 -10 |
| B - with high radiotoxicity | J-131, Bi-210, U-235, Sr-90, etc. | 10 -7 - 10 -9 |
| A - average radiotoxicity | P-32, Co-60, Sr-89, Cs-137, etc. | 10 -7 - 10 -8 |
| A - lowest radiotoxicity | C-14, Hg-197, H-3 (tritium), etc. | 10 -7 - 10 -6 |
NRB - establish the permissible concentration of all radionuclides in the air of the working area, atmosphere, water, annual intake into the body through the respiratory organs, through the digestive organs, content in a critical organ.
27. Receipt, distribution, accumulation of radioactive substances in tissues and organs and their removal from the body of animals.
Radionuclides can enter the body of animals:
· aerosol - through the lungs when inhaling polluted air;
· orally - through the digestive tract with food and water (the main route);
· resorptive - through mucous membranes, skin and wounds.
The biological effect of radionuclides during internal intake depends on the state of aggregation of the substance. The greatest effect is exerted by radioactive substances in the form of gas and water-soluble compounds. They are absorbed intensively and in large quantities into the blood, quickly spreading throughout the body or concentrated in the relevant organs. Insoluble radioactive particles can linger for a long time on the mucous membranes of the lungs and gastrointestinal tract, causing local radiation damage.
P/active aerosols less than 0.5 microns in size, entering the lungs, are almost completely removed when exhaling, particles from 0.5 to 1 microns are retained by 90%, dust particles larger than 5 microns are recorded by up to 20%. Larger particles, settling in the upper respiratory tract, are expectorated and enter the stomach. Most of the β-nuclides retained in the lungs are quickly absorbed into the blood, and some remain in the lungs for a long time.
The relative amount of radioisotope absorption by the body depends on its ratio with the carrier. Isotope carrier it is a non-radioactive isotope of this element (eg J-125 for J-131). Non-isotopic carrier - another element is a chemical analogue of a radioactive isotope (Ca for Sr-90, K for Cs-137).
The absorption and deposition of a radionuclide in tissues is directly proportional to its ratio to the carrier.
With the main route of entry of radioactive substances into the body through the gastrointestinal tract, resorption (absorption) of some radionuclides lies in the range from 100 to 0.01% (Cs, J - 100%, Sr - from 9 to 60%, Cj - 30%, Po - 6% , U-3%, Pu-0.01%).
The distribution of radionuclides in the body can be similar to the stable isotopes of these elements (for example, calcium goes to the skeletal system, iodine to the thyroid gland) or uniform throughout the body.
The following types of distribution of radioactive elements are distinguished:
uniform(H, Cs, Rb, K, etc.) - hepatic (Cerium, Pu, Th, Mg, etc.)
skeletal (osteotropic)(Ca, Sr, Ra, etc.) renal (Bi, Sbantimony, U, Asarsenic)
thyroid-stimulating(J, Br bromine).
The organ in which selective concentration of the radionuclide occurs and as a result of which it is exposed to the greatest radiation and damage) is called critical.
The lungs and gastrointestinal tract are critical organs when insoluble radionuclide compounds enter through them. For iodine, the critical organ is always the thyroid gland, for strontium, calcium, radium - always bones.
The hematopoietic system and gonads, as the most vulnerable systems even at low doses of radiation, are critical organs for all radionuclides.
The types of distribution of radionuclides in the body are the same for all species of mammals (including humans).
Young animals are characterized by more intense absorption and deposition of radionuclides in tissues. In pregnant females, radioactive isotopes pass through the placenta and are deposited in the tissues of the fetus.
Radioactive isotopes (as well as stable ones) are excreted as a result of exchange from the body with feces, urine, milk, eggs and other ways.
Biological half-life(Tb) is the time during which half of the incoming amount of an element is excreted from the body. But the loss of the isotope is accelerated in the body due to radioactive decay. (Characterized by T 1/2)
The actual loss of radionuclides from the body is expressed effective half-life , (Teff ).
Teff = (T b ·T 1/2)/(T b +T 1/2)
Let's calculate for Сs-137(T b = 0.25 years, T 1/2 = 30 years. T eff = (0.25*30)/(0.25+ 30) = 0.24 years (90 days)
Radionuclides with short Teff (Cs-137, Y-90yttrium, Ba-140, etc.), when introduced into the body once or for a short time with almost the same dose, can cause an acute or chronic course of radiation sickness, after which a rapid normalization of the blood picture occurs and the general condition of the animal.
Under the same conditions of exposure to radionuclides with high Teff (Sr-90, Ra-226 Pu-239, etc.), there is a significant difference in doses causing the acute or chronic course of the disease. The recovery period of the disease is very long, malignant tumors often arise, thrombocytopenia, anemia, infertility and other disorders persist for many years.
In animals intended for slaughter for meat, these effects may not have time to manifest themselves, but in breeding and dairy cattle the danger of their occurrence is quite real.
Animals in the human food chain serve as a kind of filter for radionuclides and reduce their entry into the human body with food.
28. Toxicology of biologically active isotope J-131.
According to the textbook
29. Toxicology of the biologically active isotope Cs-137.
According to the textbook
30. Toxicology of the biologically active isotope Sr-90.
According to the textbook
31. Modern ideas about the mechanism of biological action of ionizing radiation.
1 Modern ideas about the mechanism of biological action of i.i.
When alpha, beta particles, gamma and x-ray radiation and neutrons interact with body tissue, the following stages sequentially pass through:
-Electrical interaction penetrating radiation with atoms (time - trillionths of a second) - electron separation - ionization of the medium (this is a process of energy transfer, although in small quantities, but highly effective).
-Physico-chemical changes (billionths of a second), the resulting ions participate in a complex chain of reactions, forming products of high chemical activity: hydrated oxide HO 2, hydrogen peroxide H 2 O 2, etc., as well as free radicals H, OH (tissues at 60-70 % consists of water by mass). In a water molecule, the ratio of H to O is 2: 16 or 1: 8 (by amu). Therefore, out of 50 kg of water in a standard person weighing 70 kg, approximately 40 kg is oxygen.
-Chemical changes. Over the next millionths of a second, free radicals react with each other and with protein molecules, enzymes, etc. through a chain of oxidative reactions (not yet fully understood), causing chemical modification of biologically important molecules.
-Biological effects - metabolic processes are disrupted, the activity of enzyme systems is suppressed, DNA synthesis and protein synthesis are disrupted, toxins are formed, early physiological processes occur (inhibition of cell division, formation of mutations, degenerative changes). Cell death is possible within a few seconds or subsequent changes in it, which can lead to cancer (maybe in 2-3 decades).
Ultimately, the vital functions of individual functions or systems and the organism as a whole are disrupted.
The result of the biological effect of radiation is, as a rule, a disruption of normal biochemical processes with subsequent functional and morphological changes in the cells and tissues of the animal.
The mechanism of biological action is complex and not fully understood; there are several hypotheses and theories (London, Timofeev-Resovsky, Tarusev, Kudryashev, Kuzin, Gorizontov, etc.).
Take place:
The theory of direct and indirect action of ionizing radiation, manifested in the dilution effect and oxygen effect,
Theory of target or hits,
Stochastic (probabilistic) hypothesis,
Theory of lipid (primary) radiotoxins and chain reactions,
Structural-metabolic theory (Kuzin),
The hypothesis of an endogenous background of increased radioresistance and the immunobiological concept.
All theories explain only certain (particular) aspects of the mechanism of the primary biological action of ionizing radiation and are not fully experimentally confirmed in warm-blooded animals.
The considered stage is defined as primary (immediate) the effect of radiation on biochemical processes, functions and structures of organs and tissues.
Second phase- indirect action , is caused by neurogenic and humoral changes that occur in the body under the influence of radiation.
(Two forms of regulation in the body: nervous and humoral (interaction through liquid internal media - blood, tissue fluid, etc.) - links of a single neurohumoral regulation of functions).
The humoral or indirect effect of radiation occurs through toxic substances (radiotoxins) formed in the body during radiation sickness (the main radiation injury syndromes develop - blood changes, vomiting, etc.).
32. The effect of ionizing radiation on the cell.
1. Ionizing radiation
2. Detection and measurement methods
3. Units of measurement
4. Units of radioactivity
5. Units of ionizing radiation
6. Dosimetric values
7. Radiation reconnaissance and dosimetric monitoring devices
8. Household dosimeters
9. Radiophobia
Ionizing radiation
Ionizing radiation
- this is any radiation, the interaction of which with the environment leads to the formation of electrical charges of different signs.
During a nuclear explosion, accidents at nuclear power plants and other nuclear transformations, radiation that is not visible or perceptible to humans appears and acts. By its nature, nuclear radiation can be electromagnetic, such as gamma radiation, or it can be a stream of fast-moving elementary particles - neutrons, protons, beta and alpha particles. Any nuclear radiation, interacting with various materials, ionizes their atoms and molecules. The ionization of the environment is stronger, the greater the dose rate of penetrating radiation or the radioactivity of radiation and their prolonged exposure.
The effect of ionizing radiation on humans and animals is the destruction of living cells in the body, which can lead to varying degrees of illness, and in some cases, death. To assess the impact of ionizing radiation on humans (animals), two main characteristics must be taken into account: ionizing and penetrating abilities. Let's look at these two abilities for alpha, beta, gamma and neutron radiation. Alpha radiation is a stream of helium nuclei with two positive charges. The ionizing ability of alpha radiation in the air is characterized by the formation of an average of 30 thousand pairs of ions per 1 cm of travel. That's a lot. This is the main danger of this radiation. Penetrating ability, on the contrary, is not very great. In air, alpha particles travel only 10 cm. They are stopped by an ordinary sheet of paper.
Beta radiation is a stream of electrons or positrons at a speed close to the speed of light. The ionizing ability is low and amounts to 40 - 150 pairs of ions per 1 cm of travel in the air. The penetrating power is much higher than that of alpha radiation, reaching 20 cm in air.
Gamma radiation is electromagnetic radiation that travels at the speed of light. The ionizing ability in the air is only a few pairs of ions per 1 cm of path. But the penetrating power is very high - 50 - 100 times greater than that of beta radiation and reaches hundreds of meters in the air.
Neutron radiation is a stream of neutral particles flying at a speed of 20 - 40 thousand km/s. The ionizing capacity is several thousand pairs of ions per 1 cm of path. The penetrating power is extremely high and reaches several kilometers in the air.
Considering the ionizing and penetrating ability, we can draw a conclusion. Alpha radiation has a high ionizing and weak penetrating ability. Ordinary clothing completely protects a person. The most dangerous is the entry of alpha particles into the body with air, water and food. Beta radiation has less ionization power than alpha radiation, but greater penetrating power. Clothing can no longer provide complete protection; you need to use any kind of cover. It will be much more reliable. Gamma and neutron radiation have a very high penetrating ability; protection from them can only be provided by shelters, radiation shelters, reliable basements and cellars.
Detection and measurement methods
As a result of the interaction of radioactive radiation with the external environment, ionization and excitation of its neutral atoms and molecules occurs. These processes change the physicochemical properties of the irradiated medium. Taking these phenomena as a basis, ionization, chemical and scintillation methods are used to record and measure ionizing radiation.
Ionization method. Its essence lies in the fact that under the influence of ionizing radiation in a medium (gas volume), ionization of molecules occurs, as a result of which the electrical conductivity of this medium increases. If two electrodes are placed in it, to which a constant voltage is applied, then a directed movement of ions occurs between the electrodes, i.e. A so-called ionization current passes through, which can easily be measured. Such devices are called radiation detectors. Ionization chambers and gas-discharge counters of various types are used as detectors in dosimetric instruments.
The ionization method is the basis for the operation of such dosimetric instruments as DP-5A (B, V), DP-22V and ID-1.
Chemical method. Its essence lies in the fact that the molecules of certain substances, as a result of exposure to ionizing radiation, disintegrate, forming new chemical compounds. The amount of newly formed chemicals can be determined in various ways. The most convenient method for this is based on a change in the color density of the reagent with which the newly formed chemical compound reacts. The operating principle of the DP-70 MP chemical dosimeter for gamma and neutron radiation is based on this method.
Scintillation method. This method is based on the fact that some substances (zinc sulphide, sodium iodide, calcium tungstate) glow when exposed to ionizing radiation. The appearance of glow is a consequence of the excitation of atoms under the influence of radiation: when returning to the ground state, the atoms emit photons of visible light of varying brightness (scintillation). Visible light photons are captured by a special device - the so-called photomultiplier tube, which is capable of detecting each flash. The operation of the individual dose meter ID-11 is based on the scintillation method for detecting ionizing radiation.
units of measurement
As scientists discovered radioactivity and ionizing radiation, their units of measurement began to appear. For example: x-ray, curie. But they were not connected by any system, and therefore are called non-systemic units. All over the world there is now a unified measurement system - SI (International System). In our country, it is subject to mandatory application from January 1, 1982. By January 1, 1990, this transition had to be completed. But due to economic and other difficulties, the process is being delayed. However, all new equipment, including dosimetric equipment, as a rule, is calibrated in new units.
Units of radioactivity
The unit of activity is one nuclear transformation per second. For reduction purposes, a simpler term is used - one disintegration per second (decay/s). In the SI system, this unit is called the becquerel (Bq). In the practice of radiation monitoring, including at Chernobyl, until recently, an off-system unit of activity - the curie (Ci) - was widely used. One curie is 3.7 * 1010 nuclear transformations per second. The concentration of a radioactive substance is usually characterized by the concentration of its activity. It is expressed in units of activity per unit mass: Ci/t, mCi/g, kBq/kg, etc. (specific activity). Per unit volume: Ci/m3, mCi/l, Bq/cm3. and so on. (volume concentration) or per unit area: Ci/km3, mCi/s m2. , PBq/m2. and so on.
Units of ionizing radiation
To measure quantities characterizing ionizing radiation, the “roentgen” unit 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) - 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 - the 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 radiation dose rate 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 quantitatively account for the adverse biological effects of various types of 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- the ratio of the increment of the 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- 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- 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.
Radiation reconnaissance and dosimetric monitoring devices
Instruments designed to detect and measure radioactive radiation are called dosimetric instruments. Their main elements are a sensing device, an ionization current amplifier, a measuring device, a voltage converter, and a current source.
How are dosimetric devices classified?
First group- These are X-ray meters-radiometers. They determine the levels of radiation in the area and the contamination of various objects and surfaces. This includes the dose rate meter DP-5V (A, B) - the basic model. This device is being replaced by IMD-5.
Second group. Dosimeters for determining individual radiation doses. This group includes: dosimeter DP-70MP, a set of individual dose meters ID-11.
Third group. Household dosimetric instruments. They enable the population to navigate the radiation situation in the area and have an idea of the contamination of various objects, water and food.
Dose rate meter DP-5V designed to measure the levels of gamma radiation and radioactive contamination (contamination) of various objects (objects) by gamma radiation. The exposure dose rate of gamma radiation is determined in milliroentgens or roentgens per hour (mR/h, R/h). This device can also detect beta contamination. Gamma radiation measurement range is from 0.05 mR/h to 200 R/h. For this purpose, there are six measurement subranges. Readings are taken along the arrow of the device. In addition, a sound indication is installed, which can be heard using headphones. When contamination radioactivity is detected, the arrow deflects, and clicks are heard in the phones, and their frequency increases with increasing gamma radiation power.
Power is supplied from two 1.6 PMC type elements. The weight of the device is 3.2 kg. The procedure for preparing the device for operation and working with it is described in the attached instructions.
The procedure for measuring radiation levels is as follows. The probe screen is placed in the “G” position (gamma radiation). Then extend your hand together with the probe to the side and hold it at a height of 0.7 - 1 m from the ground. Make sure the probe stops are facing down. You can not remove the probe or take it in your hand, but leave it in the device case, but then the readings must be multiplied by the body shielding coefficient equal to 1.2
The degree of radioactivity of contaminated objects is measured, as a rule, in uncontaminated areas or in places where the external gamma background does not exceed the maximum permissible contamination of an object by more than three times.
Gamma background is measured at a distance of 15 - 20 m. From contaminated objects, similar to measuring radiation levels on the ground.
To measure the contamination of surfaces by gamma radiation, the probe screen is placed in the “G” position. Then the probe is carried out almost close to the object (at a distance of 1 - 1.5 cm). The location of the greatest infection is determined by the deflection of the arrow and the maximum number of clicks in the headphones.
Dose rate meter IMD-5 performs the same functions and in the same range. In appearance, control knobs and operating procedures, it is practically no different from the DP-5V. It has its own design features. For example, power is supplied from two A-343 elements, which ensure continuous operation for 100 hours.
Dose rate meter IMD-22 has two distinctive features. Firstly, it can measure the absorbed dose not only from gamma radiation, but also from neutron radiation, and secondly, it can be used both on mobile vehicles and on stationary objects (control points, protective structures). Therefore, it can be powered from the on-board network of a car, armored personnel carrier, or from the usual one, which is used for lighting, at 220 V. The measurement range for reconnaissance vehicles is from 1 x 10-2 to 1 x 104 rad/h, for stationary control points - from 1 to 1 x 104 rad/h.
Dosimeter DP-70MP designed to measure the dose of gamma and neutron irradiation in the range from 50 to 800 R. It is a glass ampoule containing a colorless solution. The ampoule is placed in a plastic (DP-70MP) or metal (DP-70M) case. The case is closed with a lid, on the inside of which there is a color standard corresponding to the color of the solution at an irradiation dose of 100 R (rad). The fact is that as the solution is irradiated, it changes color. This property is the basis for the operation of a chemical dosimeter. It makes it possible to determine doses for both single and multiple irradiation. The dosimeter weighs 46 g. It is carried in a clothing pocket. In order to determine the received radiation dose, the ampoule is removed from the case and inserted into the colorimeter body. By rotating the disk with filters, they look for a match between the color of the ampoule and the color of the filter, on which the radiation dose is written. If the color intensity of the ampoule (dosimeter) is intermediate between adjacent two filters, then the dose is determined as the average value of the indicated doses on these filters.
Set of individual dose meters ID-11 Designed for individual monitoring of people's exposure for the purpose of primary diagnosis of radiation injuries. The kit includes 500 individual ID-11 dose meters and a measuring device. ID-11 provides measurement of the absorbed dose of gamma and mixed gamma-neutron radiation in the range from 10 to 500 rad (roentgen). With repeated irradiation, doses are summed up and stored by the device for 12 months. The weight of ID-11 is only 25 g. It is carried in a clothing pocket.
The measuring device is made so that it can work in field and stationary conditions. Convenient to use. Has a digital reading report on the front panel.
To preserve the life and health of people, control of radioactive exposure is organized. It can be individual or group. With the individual method, dosimeters are issued to each person - usually they are received by formation commanders, reconnaissance officers, car drivers and other persons performing tasks separately from their main units.
The group control method is used for the rest of the personnel of the formations and the population. In this case, individual dosimeters are issued to one or two of the unit, group, team or to the commandant of the shelter, senior in the shelter. The registered dose is counted as an individual dose for each person and is recorded in the log book.
Household dosimeters
As a result of the Chernobyl accident, radionuclides fell over a huge area. To solve the problem of public awareness, the National Commission on Radiation Protection (NCRP) developed the “Concept for the creation and operation of a radiation monitoring system carried out by the population.” In accordance with it, people should be able to independently assess the radiation situation in their place of residence or location, including the assessment of radioactive contamination of food and feed.
For this purpose, the industry produces simple, portable and cheap instruments - indicators that provide, at a minimum, an assessment of the external radiation dose rate from background values and an indication of the permissible gamma radiation dose rate level.
Numerous instruments used by the population (thermometers, barometers, testers) measure microquantities (temperature, pressure, voltage, current). Dosimetric instruments record microquantities, that is, processes occurring at the nuclear level (the number of nuclear decays, fluxes of individual particles and quanta). Therefore, for many, the very units of measurement with which they
collide. Moreover, single measurements do not provide accurate readings. It is necessary to take several measurements and determine the average value. Then all measured values must be compared with standards in order to correctly determine the result and the likelihood of impact on the human body. All this makes working with household dosimeters somewhat specific. One more aspect that needs to be mentioned. For some reason, I got the impression that in all countries dosimeters are produced in large quantities, are sold freely and the population willingly buys them up. Nothing like this. Indeed, there are companies that produce and sell such devices. But they are not cheap at all. For example, in the USA, dosimeters cost 125 - 140 dollars, in France, where there are more nuclear power plants than we have, dosimeters are not sold to the public. But there, as the leaders say, there is no such need.
Our household dosimetric devices are truly accessible to the population, and in their performance, high level, quality and design they are superior to many foreign ones. Here are some of them: “Bella”, RKSB-104, Master-1, “Bereg”, SIM-05, IRD-02B
Radiophobia
As a result of the accident at the Chernobyl nuclear power plant, people were faced with an unusual and in many cases incomprehensible phenomenon - radiation. You cannot detect it with your senses, you cannot feel it at the moment of exposure (irradiation), you cannot see it. Therefore, all kinds of rumors, exaggerations and distortions arose. This forced some to endure enormous psychological stress, which was primarily due to poor knowledge of the properties of radiation, means and methods of protection against it.
Here, for example, is what happened at the end of 1990 in Subpolar Nadym at house 13 on Molodezhnaya Street. Someone, having a dosimeter, out of curiosity, began to measure radiation levels and established that it was supposedly twice the normal level. How he measured it, what standards he compared to, only God knows, but many perceived the conversation about the “infestation” of the house as a reliable fact. People were alarmed and rushed to flee from their apartments. Where? For what? What to call all this?
Another example. In early March 1989, in Nakhodka, a session of the city council supported the population’s demand not to allow the new nuclear ship Severomorput into the port of Vostochny. Such actions cannot be called anything other than ordinary ignorance. Don’t people know that a large number of ships with nuclear power plants have been in operation in the world for a long time and no one, not even the residents of Murmansk, where nuclear icebreakers are moored, are protesting. The crews of such ships do not suffer from radiation sickness and do not leave them in panic. For them, the word “Radiation” is well known and understandable. Some people, having heard the word “Radiation”, are ready to run anywhere but away. But there is no need to run, there is no need. Natural background radiation exists everywhere, like oxygen in the air. You shouldn't be afraid of radiation, but you shouldn't neglect it either. In small doses it is harmless and easily tolerated by humans, but in large doses it can be deadly. At the same time, it’s time to understand that radiation is not something to joke about, it takes revenge on people for it. Everyone must know firmly that a person is born and lives in conditions of constant radiation. The so-called natural radiation background is developing in the world, including cosmic radiation and radiation from radioactive elements that are always present in the earth’s crust. The total dose of these radiations, which make up the natural radiation background, varies in different areas within quite wide limits and averages 100 - 200 mrem (1-2 mSv) per year or approximately 8 - 20 μR/h.
A significant role is played by radioactive sources created by man, which are used in medicine, in the production of electrical and thermal energy, for signaling fires and making luminous watch dials, many instruments, searching for minerals and in military affairs.
Medical procedures and treatments involving the use of radioactivity are the main contributors to the dose received by humans from man-made sources. Radiation is used for both diagnosis and treatment. One of the most common devices is an X-ray machine, and radiation therapy is the main way to fight cancer. When you go to the clinic for the X-ray room, you apparently are not completely aware that you yourself, of your own free will, or rather, out of necessity, are striving to receive additional radiation. If a fluorography of the chest is to be performed, then you need to know and understand that such an action will lead to a one-time dose of 3.7 mSv (370 mrem). X-ray of the tooth will give even more - 30 mSv (3 rem). And if you are planning a fluoroscopy of the stomach, then 300 mSv (30 rem) of local radiation awaits you here. However, people do this on their own, no one forces them, and there is no panic around this. Why? Yes, because such irradiation is, in principle, aimed at healing the patient. These doses are very small, and the human body manages to heal minor radiation damage in a short period of time and restore its original state.
In medical institutions and enterprises in Russia there are hundreds of thousands of radioactive sources of various capacities and purposes. More than five thousand enterprises, organizations and institutions that use radioactive isotopes are registered in St. Petersburg and the Leningrad region alone. Unfortunately, they are stored very poorly. So, from one St. Petersburg enterprise, a worker stole a luminescent compound that was emitting radiation with might and main, and painted his slippers and light switches in his rooms with it: let them glow in the dark!
The wretchedness of man's knowledge of the nature in which he lives is striking; the dense ignorance is surprising. This little guy does not realize that he is exposing himself and his family to constant radiation, which will not lead to anything good.
The most common source of exposure is watches with luminous dials. They give an annual dose 4 times higher than that caused by leaks at nuclear power plants. Color TVs are also sources of X-ray radiation. If you watch programs every day for 3 hours for a year, this will lead to additional exposure to a dose of 0.001 mSv (0.1 mrem). And if you fly by plane, you will receive additional radiation due to the fact that the protective thickness of the air decreases with increasing altitude. Man becomes more open to cosmic rays. So when flying over a distance of 2400 km. - 10 μSv (0.01 mSv or 1 mrem), when flying from Moscow to Khabarovsk this figure will already be 40 - 50 μSv (4 - 5 mrem).
What you eat, drink, breathe - all of this also affects the doses you receive from natural sources. For example, due to the ingestion of the element potassium-40, the radioactivity of the human body increases significantly.
Food products also provide additional radiation load. Bakery products, for example, have slightly greater radioactivity than milk, sour cream, butter, kefir, vegetables and fruits. So the intake of radioactive elements inside a person is directly related to the set of foods that he eats.
We must understand that radiation surrounds us everywhere, we were born, we live in this environment, and there is nothing unnatural here.
Radiophobia is a disease of our ignorance. It can only be healed by knowledge.
The invention relates to methods for recording radiation. The method includes taking an air sample into a vessel, creating an electric field in it between two systems of conducting threads (wires) located in parallel planes relative to each other, creating an electric field strength near each thread sufficient for ionization by electron impact, and recording the number of electric pulses from alpha particles near the filaments, which determines the radioactivity of the air.
The invention relates to nuclear physics and technology, namely to methods for recording radiation. There is a known method for measuring the radioactivity of atmospheric air, which consists in taking an air sample into a vessel, measuring the number of alpha decays in it over a certain period of time, by which the radioactivity of the air is determined (Gusarov I.I., Lyapidevsky V.K., Atomic Energy vol. 10 , in 1, 1961, pp. 64 - 67). As a result of the analysis of the level of technology, the closest analogue (prototype) of the dried method was established (US patent N 4977318, class G 01 T 1/18, 1990). A known method for measuring the radioactivity of atmospheric air involves taking a sample into a chamber in which an electric field is created between parallel electrodes, one of which is at a positive potential and the other at a negative potential. The electric field strength is selected sufficient for impact ionization of the gas. The radioactivity of air and the content of radioactive impurities in it are determined separately by attracting negatively and positively charged particles to the corresponding charged electrodes. The disadvantage of the prototype is the use of a flat chamber in which an electric field is created between parallel electrodes, and the electric field strength is selected sufficient for impact ionization. Thus, the chamber in which air radioactivity is determined is a gas-discharge detector with two flat electrodes and gas amplification. A significant disadvantage of such a detector with two flat electrodes is the exponential dependence of the amplitude of the recorded pulses on the distance to the positive electrode of the ionization produced in the detector (Lyapidevsky V.K. Methods for detecting radiation. M. Energoatomizdat, 1987, p. 225). In addition, flat panel detectors require careful alignment. Therefore, at present, detectors with flat geometry are practically not used. Proportional wire chambers with flat geometry have significantly better characteristics (Lyapidevsky V.K., Methods of radiation detection, M:, Energoatom-izdat, 1987 p. 320) The flat chamber module is a system of wire electrodes located in the same plane, located between the wire or solid electrodes. The wires form a system of proportional detectors. Proportional cameras are widely used in physical experiments. Taking into account the current level of technology, the proposed invention uses a wire (filament chamber). The purpose of the invention is to create a method for measuring air radioactivity using a stable operating mode of a wire detector (a detector with a system of conductive threads). The goal is achieved through the use of plane-parallel multi-wire chambers filled with air and the creation near each wire (conducting thread) of an electric field strength sufficient to cause ionization by electron impact to occur near each wire. The essence of the invention is that to measure the radioactivity of atmospheric air, an air sample is taken into a vessel (chamber), and the number of alpha particle pulses is measured in it over a certain period of time using a detector, which is used to determine the radioactivity of the air. The proposed method differs from the known ones in that an electric field is created in the volume of the vessel (chamber) between two systems of wire (filament) electrodes with a diameter of 10 - 100 microns located in two planes parallel to each other, and in one plane all the threads are positively charged, and in the other - negatively during the time of implementation of the method. Near each filament, an electric field strength is created sufficient for electron impact ionization to occur near each filament, and the radioactivity of the air and the radioactive impurities contained in it is determined by the number of electrical impulses from alpha particles recorded separately near the positively charged filaments and near the negatively charged filaments. With an increase in the potential difference and with a large number of carrying impurities, the discharge near the filament turns into a corona (Geiger-Muller counter mode) and into a streamer (Lyapidevsky V.K. Methods for detecting radiation, M: Energoatomizdat, 1987, p. 232) Unlike In the case of a streamer discharge arising in a uniform field between two flat electrodes, the streamer formed near the wire during its development falls into the region of a weak electric field. The streamer stops at a considerable distance from the wire (thread), where the electric field strength is significantly lower than near the thread. In Fig. 8.10 p. 236, cited from the textbook by Lyapidevsky V.K., shows all the operating modes that arise when the electric field strength increases near the filament of a gas-filled detector. Information confirming the possibility of implementing the invention. Gas-filled chambers containing current-conducting wires (threads) located in two planes parallel to each other are widely used in physical experiments (Materials of a workshop on the method of proportional chambers, Dubna, March 27-30, 1973, p. 102 - 103 and Fig. 1 on page 103). A similar model was made at the request of the author at the Laboratory of Nuclear Problems of JINR, tested by the author and is currently located at MEPhI. The widespread use of wire chambers in physics and technology confirms the possibility of implementing the invention.
Claim
A method for measuring the radioactivity of atmospheric air, which consists in taking an air sample into a vessel, measuring it over a certain period of time using a detector of the number of alpha particle pulses, which determines the radioactivity of the air, characterized in that an electric field is created in the volume of the vessel between two located in parallel planes, systems of conducting threads with a diameter of 10 - 100 microns each, and in one plane all the threads are positively charged, and in the other - negatively during the time of implementation of the method, create an electric field strength sufficient for the occurrence of ionization near each thread by electron impact, and in number electrical impulses from alpha particles, recorded separately near positively charged threads and near negatively charged threads, determine the radioactivity of the air and the radioactive impurities contained in it.
Similar patents:
The invention relates to techniques for using accelerated electron beams, namely to systems for monitoring electron beams of accelerators, and is intended for use primarily in medicine, in devices for radiation therapy
The invention relates to techniques for measuring ionizing radiation and can be used in radiation and dosimetric instruments or in nuclear reactor control systems. Compensation ionized chambers are known, in which precise adjustment of compensation is carried out by changing the degree of current saturation in the compensation part when adjusting the potential of the high-voltage electrode. However, a decrease in the degree of saturation below 100% disrupts the linearity of the operating characteristics of the ionization chamber. The closest to the invention is an ionizing radiation detector containing two ionization chambers connected in opposite directions and formed by the surfaces of the high-voltage and control electrodes and a collecting electrode placed between them
Express methods for determining radioactivity in any objects they make it possible to measure the specific activity of a sample or surface radioactive contamination directly (expressly) without the so-called enrichment of the measured samples, that is, without concentrating radioactive substances in the sample material (evaporation, ashing, pressing, chemical enrichment, etc.).
In the laboratories of SES, Gosagroprom, Ukoopsoyuz, trade organizations and other ministries and departments, they are currently using the “Method for the rapid determination of volumetric and specific activity of beta-emitting nuclides in water, food, crop and livestock products by the method of “direct” measurement of “thick” samples .
There are five main operations in it:
- selection and preparation of samples of the studied material for measurements;
- preparing the Beta radiometer or other device you have for operation;
- background measurement;
- measuring samples of the material under study (food products, raw materials, water and other environmental objects);
- calculation of radioactivity (specific mass or volumetric activity) of samples and comparing them with the permissible norm.
Selection and preparation of samples of the studied material for measurements. For a systematic analysis of your research over several months or a number of years, you should keep a journal in which you record the date, type of product measured, type of device (it may change in a year or two), location of sampling (for example, in which forest and when collected mushrooms, berries, etc.) and the results of measurements (calculations).
Plant sampling As a rule, they are carried out in the same areas as soil samples. To obtain a combined plant sample weighing 0.5-1 kg of natural moisture, it is recommended to take at least 8-10 point samples. The above-ground part of the grass cover is cut off with a sharp knife or scissors (without clogging with soil), placed in a plastic bag, and a label made of cardboard or thick paper is inserted, on which the name of the plant, the growing season phase, the place of selection, the type of product selected and the date are noted.
The lower parts of plants are often contaminated with soil. In this case, you either need to cut the plants higher, or thoroughly wash the material with distilled water. Agricultural crops should be sampled along a field diagonal or a broken curve. The combined sample is made up of 8-10 point samples taken either from the above-ground parts of plants or separately - stems and leaves, fruits, grains, roots, tubers.
Grain sampling produced throughout the entire depth of the grain mound or bag. Using a hand probe, point samples are taken from the upper and lower layers, touching the bottom with the probe. The total mass of spot samples during sampling must be at least 1 kg. The grain is mixed.
Samples of tubers and root vegetables taken from piles, embankments, heaps, vehicles, trailers, wagons, barges, storage facilities and directly from the ground. Samples are taken from a homogeneous batch of any quantity, one variety, harvested from one field, stored under the same conditions.
Point samples are taken diagonally along the side surface of the pile, embankment, heaps at equal distances at a depth of 20-30 cm. Tubers and root crops are taken at three points in a row.
The average sample for analysis is isolated from the combined sample; its weight should be 1 kg.
Grass and green mass sampling. From pastures or hayfields, samples are taken immediately before grazing animals or mowing for food, for which 8-10 recording areas measuring 1 or 2 m 2 are allocated in the area selected for sampling, placing them diagonally across the area. The grass stand is mowed (cut) at a height of 3-5 cm. The green mass obtained from all point samples or counting areas is collected on the canopy, thoroughly mixed and spread in an even layer, thus obtaining a combined sample, from which an average sample is taken for analysis. To compile an average sample, the mass of which should be 1 kg, the grass is taken in portions of 100 g from 10 different places.
Roughage samples, stored in stacks, stacks are selected along the perimeter of the stacks, stacks at equal distances from each other at a height of 1-1.5 m from the surface of the earth from all accessible sides from a depth of at least 0.5 m.
Product sampling(cereals, legumes, seeds, etc.) is similar to grain sampling methods. Apples, tomatoes, eggplants, etc. are selected using the method of selecting root crops, etc. From small batches of products (berries, herbs, etc.), spot samples are taken in four to five places. The combined sample, by weight or volume, shall not exceed three times the quantity required for measurement on the appropriate instrument.
Milk and dairy products are collected from small containers (cans, flasks, etc.). They are taken after mixing, and from large ones (tank, vat) - from different depths of the container with a mug with an elongated handle or a special sampler. The average sample size is 0.2-1 liters and depends on the size of the entire batch of products.
Sampling of meat, organs of farm animals and poultry They are carried out at slaughterhouses on collective farms, state farms, meat processing plants, markets, on private farms, and also in shops.
Meat samples (without fat) from carcasses or half-carcasses are taken in pieces of 30-50 g in the area of the fourth-fifth cervical vertebrae, shoulder blade, thigh and thick parts of the spinal muscles. The total sample mass should be 0.2-0.3 kg. For a special laboratory study, bones in the amount of 0.3-0.5 kg (spine and second-third rib) are also selected. Samples of the internal organs of animals are taken in quantities: liver, kidneys, spleen, lungs - 0.1 - 0.2 kg, thyroid gland - the entire organ. Poultry (chickens) are taken whole carcasses. Chickens, turkeys, ducks, geese - up to 1/4 of the carcass. The number of samples is determined by the volume and nature of the research.
Fish sampling They are produced in fish factories, cold storage plants, markets, shops, and also when caught directly in water bodies. Small fish specimens are taken whole carcasses, large ones - only their middle part. All types of fish are subject to research. The weight of an average sample is 0.3-0.5 kg. The number of samples is determined by the volume and nature of the research.
Egg samples are selected from poultry farms, poultry farms of state farms, collective farms, at the market, in stores and personal farms. Sample size is 2-3 eggs.
Natural honey sampling produced in apiaries, shops, markets, warehouses and bases of farms and consumer cooperatives.
Honey is collected using a tubular aluminum sampler (if the honey is liquid) or an oil probe (if the honey is dense) from different layers of the product. Crystallized honey is selected with a conical probe, immersing it into the honey at an angle. When studying comb honey, a part of the comb with an area of 25 cm 2 is cut out from one honeycomb frame. If the comb honey is in lumps, a sample is taken in the same volumes from each package. After removing the wax caps, honey samples are placed on a mesh filter with a cell diameter of no more than 1 mm, placed in a glass, and placed in the oven of a gas stove at a temperature of 40-45 ° C. The weight of an average sample is 0.2-0.3 kg.
Samples of wool, technical bone, horn-hoofed animals, fur raw materials and skins are selected in a similar way, followed by mechanical crushing or grinding. Sample weight - 100-200 g.
Sampling of juices, syrups, jams, water, compotes produced from a mixed, homogeneous mass. Sample weight - 100-200 g.
Samples of prepared meat products and sausages are selected when they are transferred to the distribution network, directly in stores or in storage areas. The weight of samples of finished meat products, semi-finished products and sausages is 200-300 g.
If necessary, the selected samples are cleaned, washed and crushed. Food samples are processed as in the first stage of food preparation. Root vegetables, tubers and potatoes are washed in running water. Inedible leaves are removed from cabbage. Food greens, berries and fruits are also washed with running water. Meat and fish are washed, scales and entrails are removed from the fish. The casing is removed from the sausages, and the paraffin layer is removed from the cheese. Prepared products are ground using a meat grinder, grater, coffee grinder, etc. Food greens, grass, hay, etc. are ground with a knife in an enamel cuvette.
To measure on the Beta radiometer, the crushed material is placed into a special cuvette using a spatula or spoon and compacted. Excess from the surface is removed so that the product is flush with the upper edges of the trough. When testing water, milk and other liquid and pasty food products, the trough is filled with a controlled sample.
Preparing the device for operation. Preparation of Beta, SRP-68-01 and other instruments for measuring samples, radioactive contamination of surfaces or background is described in the previous section.
Background measurements. This operation is carried out in an empty, clean (decontaminated) trough cup, or it can be filled with distilled water.
The background is measured before the start of the study of material samples and at its completion. If there are a lot of samples and measurements are carried out for a long time, then repeated (intermediate) background measurements are made every 2 hours of work. Then all background measurements are summed up and its average value is determined, which is used in calculating the activity of the materials under study.
Measurements of samples of the studied material. The sample prepared for the study is inserted into a lead house and measured under the same conditions as the background was measured (the same distance from the counter and measurement time). On the Beta radiometer and other instruments, as a rule, one measurement of the sample is made within 1000 s, or two measurements of 100 s each, or three measurements of 10 s each, and the average is calculated from the two closer values.
Proper filling of a cup, cuvette or trough with sample material then allows the obtained values of the specific activity of the sample to be automatically transferred to a kilogram of mass or a liter of volume of the test material without additional weighing and recalculation. This is provided for by the design of the device. That is why it is important to ensure that the container being measured is correctly filled and to avoid underfilling (or underfilling) of the sample material, as well as overfilling.
Calculation of sample radioactivity. Since professional radiometers do not directly measure the radioactivity of the material of the test sample, but determine its proportional value N (the counting rate of pulses recorded by the device counter per unit time), the radioactivity (specific activity) is determined by calculation using the formulas:
N = (N etc - N f) / t; A=K N(or A = N/ P
Where N pr - counting rate of the pulse repetition rate when measuring radioactive contamination of a “thick” layer of a sample of the material under study (taking into account the background), imp.; N f - average background count rate (with an empty cuvette or filled with distilled water), imp.; t- background and sample measurement time, s/min); K - conversion factor (taken from the device passport), Ki. s (min)/l (kg) . imp.; P - sensitivity of the radiometer P = 1/K; A is the specific volume (Ci/l) or specific mass (Ci/kg) activity of the sample being measured.
Example. Let’s say that you need to measure dry brewed tea (Georgian, grade I) using the Beta radiometer. On the device N f1 turned out to be equal to 20 imp. behind t=10 s, a N f, = 19 and N f = 21 imp. The average background value over 10 s of measurements will be 20 pulses.
We measure the tea sample three times within 10 seconds. We get: N pr = 30 imp., N pr2 = 34 and N pr3 = 32 imp. Average value N pr = 32 imp.
The coefficient in this case is equal to:
K = 5.26. 10 -8 Ci. s/kg. imp.;
A = N K = 1.2 pulses/s. 5.26. 10 -8 Ci. s/kg. imp. = 6.3. 10 -8 Ci/kg.
The permissible norm for tea (dry brewing) is 5. 10 -7 Ci/kg, thus we see that the tea we measured is within the normal range, that is, almost eight times lower than the norm.
However, it should be noted that since 1988, the State Standard of the USSR has added to this calculation methodology to take into account the natural isotope potassium-40. The first formula for calculating activity took the form:
|
According to the formula N = |
N etc - N f |
||
Where N K is selected from a table of potassium-40 content in various products and raw materials.
This change in calculations is explained by the fact that in recent years, due to excessive chemicalization of fields and, in particular, the use of potassium fertilizers, a significant amount of radioactive potassium (potassium-40) has been supplied to crop and livestock products, and consequently, its share in measurements of the radioactivity of products has become significant and subject to accounting.
Let's consider how to convert some quantities into others and what relationships exist between individual dosimetric units. For example, between milliroentgens and curies, curies and rem, etc.
These are units of completely different physical quantities, although they all characterize radioactivity or its effects and therefore do not have strict mathematical relationships. Tentatively, very approximately, and only for a specific region and a “bouquet” of radionuclides from practice (on an empirical basis), some relationships can be proposed. Thus, the level of radiation (background) and pollution for a certain area can be determined from the ratios given in table. 4.
4. The relationship between the level of radiation and land pollution
|
Land pollution, Ci/km 2 |
|
Knowing the level of radiation in a given place, one can roughly judge the radionuclide contamination of a given area, and vice versa.
The relationships between the same quantities in traditional units and SI units are strictly regulated and their mathematical values are given in Appendix 1.
Example. Let's say the radiation level was measured with a dosimeter and a value of 0.020 mR/h (20 μR/h) was obtained. Let's determine what dose a person will receive from this background while being on the street for one day, month or year, multiplying the dose per hour by the corresponding time. We get: per hour - 20 microR, day - 480 microR, month -14,400 microR, year - 172.8 microR.
But since a person spends a certain amount of time (more than 50%) in an office or residential building, he will naturally receive a smaller dose. For example, indoors the dosimeter showed a value of 0.01 mR/h (or 10 μR/h). This means he will receive a dose: per day - 240 mR, per month - 7200 mR (7.2 mR), per year - 86.4 mR.
If we assume that this person, due to his type of work and living conditions, spends an average of 50% of his time outdoors per year and 50% indoors, then the dose will be average: 15 microR per hour, 360 microR per day, 10,800 microR per month. (10.8 mR), per year - 130 mR. Well, to be more precise, a person will receive not 130 mR, but 130 mrem, since a rem (biological equivalent of an x-ray) is the equivalent dose of human radiation.
Now let’s determine the attenuation coefficient of the indoor background radiation of a person in an open area. Let's take the same values: outside the background is 20 µR/h, and indoors - 10 µR/h:
TO ovl = 20/10 = 2
i.e., this room reduces a person’s external exposure by half. This coefficient is also called the protection coefficient. In this case, we calculated the coefficient of protection from human radiation by the walls of the room.
Let us present an empirical relationship for the radioactivity of food products. Thus, the exposure dose rate (EDR) measured by the Poisk (or other) device, caused by gamma-emitting radionuclides of a food product, in microroentgens per hour can be approximately converted into units of specific radioactivity curie per kilogram or curie per liter:
| DER, µR/h | Activity, ki/kg |
Note. Data for the Poisk device (based on the cesium-137 standard) and for samples with a density equal to unity.
Of all the household dosimeters and radiometers intended for the public, only the Bella device is calibrated not in traditional, but in international SI units - microsieverts (equivalent dose units). Roughly, they can be converted into traditional ones (micro-roentgens). Let us turn to the description of the device “Operating Manual” and the attached “Methodological Instructions”, approved by the Deputy Director of the Institute of Biophysics of the USSR Ministry of Health, Academician L. A. Buldakov on 09/07/1989.
Measuring range: 0.2-100 µSv/h. This corresponds to: 20-10 thousand microR/h. For accurate translation: μSv = 104 μR.
The natural background dose rate is about 0.15 μSv/h (15 μR/h) and, depending on local conditions, can vary by a factor of two.
For the population living near nuclear power plants, the National Commission on Radiation Protection (NK.RZ) has set an annual dose limit of 5 mSv, which corresponds to 500 mrem or 500 mR (since rem is the biological equivalent of an x-ray, 1 rem = 1.04 R ).
If the radioactive contamination of the food product being measured reaches 3700 Bq (>4 kBq), then the readings of the Bella device will increase from the background of the area by 0.15 μSv/h (15.6 μR/h). This corresponds to 1. 10 -7 Ci/kg (Ci/l) of radioactive contamination and it is recommended to refuse the consumption of such food products or limit their consumption in the normal diet by half, four, ten times (depending on the degree of contamination).
This latest recommendation from the USSR Ministry of Health is mandatory for all devices: if the measured radioactive contamination is 1 10~7 Ci/kg (Ci/l) and higher, then such food products cannot be consumed by adults (and especially children). They require either special processing (see recommendations in Chapter III), cleaning or “dilution” with pure products.
The radioactivity of drugs can be determined by the absolute, calculated and relative (comparative) method. The latter is the most common.
Absolute method. A thin layer of the material under study is applied to a special thin film (10-15 μg/cm²) and placed inside the detector, as a result of which the full solid angle (4) is used to register emitted, for example, beta particles and almost 100% counting efficiency is achieved. When working with a 4 counter, you do not need to introduce numerous corrections, as with the calculation method.
The activity of the drug is expressed immediately in units of activity Bq, Ku, mKu, etc.
By calculation method determine the absolute activity of alpha and beta emitting isotopes using conventional gas-discharge or scintillation counters.
A number of correction factors are introduced into the formula for determining the activity of a sample, taking into account radiation losses during measurement.
A =N/ q r m 2,22 10 ¹²
A- activity of the drug in Ku;
N- counting rate in imp/min minus background;
- correction for geometric measurement conditions (solid angle);
-correction for the resolving time of the counting installation;
-correction for radiation absorption in the air layer and in the window (or wall) of the counter;
-correction for self-absorption in the drug layer;
q-correction for backscattering from the substrate;
r- correction for the decay scheme;
-correction for gamma radiation with mixed beta and gamma radiation;
m- weighed portion of the measuring drug in mg;
2,22 10 ¹² - conversion factor from the number of disintegrations per minute to Ci (1Ci = 2.22*10¹²dissolution/min).
To determine the specific activity, it is necessary to convert the activity per 1 mg to 1 kg .
Audi= A*10 6 , (TOu/kg)
Preparations for radiometry can be prepared thin, thick or intermediate layer the material being studied.
If the material being tested has half attenuation layer - 1/2,
That thin
- at d<0,11/2,
intermediate
- 0,11/2
All correction factors themselves, in turn, depend on many factors and, in turn, are calculated using complex formulas. Therefore, the calculation method is very labor-intensive.
Relative (comparative) method has found wide application in determining the beta activity of drugs. It is based on comparing the counting rate from a standard (a drug with known activity) with the counting rate of the measured drug.
In this case, there must be completely identical conditions when measuring the activity of the standard and the test drug.
Apr = Aet*Netc/Nthis, Where
Aet - activity of the reference drug, dis/min;
Apr - radioactivity of the drug (sample), dispersion/min;
Net is the counting rate from the standard, imp/min;
Npr - counting rate from the drug (sample), imp/min.
The passports for radiometric and dosimetric equipment usually indicate with what error the measurements are made. Maximum relative error measurements (sometimes called the main relative error) is indicated as a percentage, for example, 25%. For different types of instruments it can be from 10% to 90% (sometimes the error of the type of measurement is indicated separately for different sections of the scale).
Based on the maximum relative error ± %, you can determine the maximum absolute measurement error. If readings from instrument A are taken, then the absolute error A = A/100. (If A = 20 mR, a =25%, then in reality A = (205) mR. That is, in the range from 15 to 25 mR.
Detectors of ionizing radiation. Classification. Principle and operating diagram of a scintillation detector.
Radioactive radiation can be detected (isolated, detected) using special devices - detectors, the operation of which is based on the physical and chemical effects that arise when radiation interacts with matter.
Types of detectors: ionization, scintillation, photographic, chemical, calorimetric, semiconductor, etc.
The most widely used detectors are based on measuring the direct effect of the interaction of radiation with matter - ionization of the gaseous medium. These are: - ionization chambers;
- proportional counters;
- Geiger-Muller counters (gas-discharge counters);
- corona and spark counters,
as well as scintillation detectors.
Scintillation (luminescent) The radiation detection method is based on the property of scintillators to emit visible light radiation (light flashes - scintillations) under the influence of charged particles, which are converted by a photomultiplier into electric current pulses.
Cathode Dynodes Anode The scintillation counter consists of a scintillator and
PMT. Scintillators can be organic and
inorganic, in solid, liquid or gas
condition. This is lithium iodide, zinc sulfide,
sodium iodide, angracene single crystals, etc.
100 +200 +400 +500 volts
PMT operation:- Under the influence of nuclear particles and gamma quanta
In the scintillator, atoms are excited and emit quanta of visible color - photons.
Photons bombard the cathode and knock photoelectrons out of it:
Photoelectrons are accelerated by the electric field of the first dynode, knock out secondary electrons from it, which are accelerated by the field of the second dynode, etc., until an avalanche flow of electrons is formed that hits the cathode and is recorded by the electronic circuit of the device. The counting efficiency of scintillation counters reaches 100%. The resolution is much higher than in ionization chambers (10 v-5 - !0 v-8 versus 10¯³ in ionization chambers). Scintillation counters find very wide application in radiometric equipment
Radiometers, purpose, classification.
By appointment.
Radiometers - devices intended for:
Measurements of the activity of radioactive drugs and radiation sources;
Determination of flux density or intensity of ionizing particles and quanta;
Surface radioactivity of objects;
Specific activity of gases, liquids, solids and granular substances.
Radiometers mainly use gas-discharge counters and scintillation detectors.
They are divided into portable and stationary.
As a rule, they consist of: - a detector-pulse sensor; - a pulse amplifier; - a converting device; - an electromechanical or electronic numerator; - a high voltage source for the detector; - a power supply for all equipment.
In order of improvement, the following were produced: radiometers B-2, B-3, B-4;
dekatron radiometers PP-8, RPS-2; automated laboratories “Gamma-1”, “Gamma-2”, “Beta-2”; equipped with computers that allow the calculation of up to several thousand sample samples with automatic printing of results. DP-100 installations, KRK-1, SRP-68 radiometers are widely used -01.
Indicate the purpose and characteristics of one of the devices.
Dosimeters, purpose, classification.
The industry produces a large number of types of radiometric and dosimetric equipment, which can be classified:
By the method of recording radiation (ionization, scintillation, etc.);
By type of detected radiation (,,,n,p)
Power source (mains, battery);
By place of application (stationary, field, individual);
By appointment.
Dosimeters - devices that measure exposure and absorbed dose (or dose rate) of radiation. Basically consist of a detector, an amplifier and a measuring device. The detector can be an ionization chamber, a gas-discharge counter or a scintillation counter.
Divided into dose rate meters- these are DP-5B, DP-5V, IMD-5, and individual dosimeters- measure the radiation dose over a period of time. These are DP-22V, ID-1, KID-1, KID-2, etc. They are pocket dosimeters, some of them are direct-reading.
There are spectrometric analyzers (AI-Z, AI-5, AI-100) that allow you to automatically determine the radioisotope composition of any samples (for example, soils).
There are also a large number of alarms indicating excess background radiation and the degree of surface contamination. For example, SZB-03 and SZB-04 signal that the amount of hand contamination with beta-active substances is exceeded.
Indicate the purpose and characteristics of one of the devices
Equipment for the radiological department of the veterinary laboratory. Characteristics and operation of the SRP-68-01 radiometer.
Staff equipment for radiological departments of regional veterinary laboratories and special district or inter-district radiological groups (at regional veterinary laboratories)
Radiometer DP-100
Radiometer KRK-1 (RKB-4-1em)
Radiometer SRP 68-01
Radiometer “Besklet”
Radiometer - dosimeter -01Р
Radiometer DP-5V (IMD-5)
Set of dosimeters DP-22V (DP-24V).
Laboratories can be equipped with other types of radiometric equipment.
Most of the above radiometers and dosimeters are available at the department in the laboratory.
Periodization of hazards during a nuclear power plant accident.
Nuclear reactors use intranuclear energy released during fission chain reactions of U-235 and Pu-239. During a fission chain reaction, both in a nuclear reactor and in an atomic bomb, about 200 radioactive isotopes of about 35 chemical elements are formed. In a nuclear reactor, the chain reaction is controlled, and nuclear fuel (U-235) “burns out” in it gradually over 2 years. Fission products - radioactive isotopes - accumulate in the fuel element (fuel element). An atomic explosion cannot occur in a reactor either theoretically or practically. At the Chernobyl nuclear power plant, as a result of personnel errors and a gross violation of technology, a thermal explosion occurred, and radioactive isotopes were released into the atmosphere for two weeks, carried by winds in different directions and, settling over vast areas, creating spotty pollution of the area. Of all the r/a isotopes, the most biologically hazardous were: Iodine-131(I-131) – with a half-life (T 1/2) 8 days, Strontium - 90(Sr-90) - T 1/2 -28 years and Cesium - 137(Cs-137) - T 1/2 -30 years. As a result of the accident, 5% of the fuel and accumulated radioactive isotopes were released at the Chernobyl nuclear power plant - 50 MCi of activity. For cesium-137, this is equivalent to 100 pieces. 200 Kt. atomic bombs. Now there are more than 500 reactors in the world, and a number of countries provide 70-80% of their electricity from nuclear power plants, in Russia 15%. Taking into account the depletion of organic fuel reserves in the foreseeable future, the main source of energy will be nuclear.
Periodization of hazards after the Chernobyl accident:
1. period of acute iodine danger (iodine - 131) for 2-3 months;
2. period of surface contamination (short- and medium-lived radionuclides) - until the end of 1986;
3. period of root entry (Cs-137, Sr-90) - from 1987 for 90-100 years.
Natural sources of ionizing radiation. Cosmic radiation and natural radioactive substances. Dose from ERF.
Loading...