Correct answer:
A) Increases with increasing dose rate.
D) Decreases when receiving doses in small portions.
E) Different for limbs and internal organs.
(IES-023-ORB, clause 4; NRB-99, clause 9)
Biological effect of AI
4.1 In first place in terms of radiation hazard is a-radiation due to its high ionizing ability. However, its external irradiation can be neglected, because a - particles do not reach radiation-sensitive cells; Particularly dangerous is the entry of a-emitters into the body.
Fast neutrons are in second place in terms of radiation hazard. They, experiencing elastic collisions with light tissue nuclei (hydrogen), form recoil protons, causing a high ionization density.
b and g emissions have the same emissivity weighting factor (see Appendix B). The slightly higher ionization density of beta radiation is compensated by the smaller volume of irradiated tissue due to lower penetrating power. Fluxes of b - radiation mainly affect the integumentary tissues, eyes, and can cause dryness and burns of the skin, fragility and brittleness of nails, and clouding of the lens.
It is especially dangerous if RAVs enter the body due to:
- increasing the irradiation time (round-the-clock irradiation);
- reducing the attenuation of the radiation flux (occurs closely);
- impossibility of applying protection;
- selective deposition in body tissues (for example: strontium (Sr), plutonium (Pu) - in the skeleton; cerium, lanthanum - in the liver; ruthenium, cesium - in muscles; iodine - in the thyroid gland).
The most dangerous isotopes are those that have a long half-life and are deposited near the bone marrow (in the bones) Sr and Pu.
The half-life of radionuclides from the body is determined by the physicochemical properties of the radioactive substances and the state of the body; daily routine, proper use of therapeutic and preventive nutrition.
4.2 Interaction of AI with biological tissue leads to ionization and excitation of atoms, rupture chemical bonds, the formation of chemically highly active compounds, so-called “free radicals”. Radicals can cause modification of molecules necessary for normal cell functioning.
Since the body is 75% water, the reaction mechanism operates by ionizing its molecules to form hydrogen peroxide H 2 O 2, hydrate oxides that interact with cell molecules and lead to the breaking of chemical bonds.
Defeats cellular structures lead to disruptions in the activity of the nervous system, processes regulating the activity of tissues and organs, regeneration, and cell renewal. The most radiosensitive cells are the cells of constantly renewed tissues and organs (bone marrow, spleen, genital organs).
Disturbances in the system of hematopoietic organs (primarily red bone marrow) lead to a decrease in the amount of:
- white blood cells (leukocytes), limiting the body's defenses in the fight against infections;
- blood platelets (platelets), impairing blood clotting;
- red blood cells (erythrocytes), impairing the supply of oxygen to cells.
If the walls of blood vessels are damaged, hemorrhages, blood loss and disruption of the functioning of organs and systems are possible.
4.3. With small doses of radiation and a healthy body, the affected tissue restores its functional activity. The damaging effect of irradiation increases with increasing dose rate and the size of the dose received at a time and decreases somewhat when doses are received in small portions.
With a single irradiation of the whole body with a dose of up to 0.25 Gy (25 rad), changes in the composition of health are not detected. With an absorbed dose of 0.25¸ 0.5 Gy (25¸ 50 rad), there are also no external signs of radiation damage; changes in the blood can be observed, which soon return to normal.
Red bone marrow and other elements of the hematopoietic system are most vulnerable to radiation, losing the ability to function normally at doses of 0.5¸ 1 Gy (50¸ 100 rad). However, if damage to all cells is not caused, then the hematopoietic system, thanks to its ability to regenerate, restores its functions. After irradiation, there is a feeling of fatigue without serious loss of ability to work; less than 10% of those exposed may experience vomiting and changes in blood composition.
4.4 In the case of a single exposure to a dose of more than 1 Gy (100 rad), various forms of radiation sickness occur:
4.4.1 With irradiation of 1.5¸ 2 Gy (150¸ 200 rad) – a short-term mild form of acute radiation sickness, manifested in the form of severe lymphopenia (decreased number of lymphocytes). In 30-50% of cases, vomiting may be observed in the first day after irradiation; there are no deaths.
4.4.2 When exposed to 2.5¸ 4 Gy (250¸ 400 rad), moderate radiation sickness occurs, accompanied by vomiting on the first day. The number of leukocytes sharply decreases, subcutaneous hemorrhages appear. In 20% of cases, death is possible 2-6 weeks after irradiation.
4.4.3 At a dose of 4¸ 6 Gy (400¸ 600 rad), a severe degree of radiation sickness develops, with 50% of deaths within a month after irradiation.
4.4.4 An extremely severe degree of radiation sickness develops at doses above 6-7 Gy (600-700 rad), accompanied by vomiting 2-4 hours after irradiation. Leukocytes almost completely disappear in the blood, subcutaneous and internal (mainly in the gastrointestinal tract) hemorrhages appear. Due to infectious diseases and bleeding, the mortality rate in this case is close to 100%.
4.4.5. All of the above data refer to irradiation without subsequent therapeutic intervention, which, with the help of anti-radiation drugs, can significantly reduce the impact of IS. The success of treatment largely depends on the timely provision of first aid.
4.4.6 At doses lower than those causing acute radiation sickness, but systematically significantly higher dose limits, chronic radiation sickness, a decrease in the number of leukocytes, and anemia can develop.
4.5. In addition to radiation sickness under the influence of radiation, local damage to organs is possible, which also has a pronounced dose threshold:
4.5.1 Irradiation with a dose of 2 Gy (200 rad) can lead to long-term (for years) deterioration in the performance of the testes; disturbances in the activity of the ovaries are observed at doses of more than 3 Gy (300 rad).
4.5.2 Long-term (15-20 years) irradiation of the eye lens with a dose of 0.5-2 Gy (50-200 rad) can lead to an increase in its density, clouding, and gradual death of its cells, i.e. cataract.
4.5.3 Most internal organs are capable of withstanding large doses - tens of grays (classified as “others” by the tissue weighting factor). Cosmetic skin defects are noted at doses of ~20 Gy (2000 rad).
4.6 Low doses of radiation (less than 0.5 Gy) can initiate long-term effects - cancer or genetic damage.
The body's reaction to the effects of radiation can manifest itself in a long period (10-15 years) after irradiation - in the form of leukemia, skin lesions, cataracts, tumors, fatal and non-fatal cancers.
In the nuclei of the body's cells there are 23 pairs of chromosomes, which double during division and are arranged in a certain order in the daughter cells, ensuring the transfer of hereditary properties from cell to cell. Chromosomes consist of large molecules of deoxyribonucleic acids, changes in which can lead to the formation of daughter cells that are not identical to the original ones. The appearance of such changes in germ cells can lead to adverse consequences in the offspring. In this case, deviations are most likely to occur when a gene is connected to another that has the same disorder. This is where the provisions of the Belarusian norms on limiting the number of irradiated persons come from.
4.7 The emergence of malignant neoplasms and genetic damage is caused by many environmental factors and is of a probabilistic nature, which can only be quantified for a large number people, i.e. statistical methods
Available radiobiological data make it possible to reliably assess the incidence of adverse effects only at relatively large doses, greater than 0.7 Gy (70 rad). In the absence of acute radiation injuries, it is almost impossible to establish a causal relationship between radiation exposure and the appearance of long-term consequences, because they may also be caused by other non-radiation factors. The radiation dose leads to an increase in the probability, an increase in the risk of adverse consequences for the body, the greater the higher the dose. Quantitative risk estimates at low doses were obtained by extension, extrapolation of the dose-effect relationship from the high-dose region (0.7¸ 1 Gy), as well as animal experiments. At the same time, the effects of the body's reaction, which can only be assessed by statistical methods, consequences, the probability of which exists at any small doses (however, the dose does not lead to these consequences in all cases) and increases with increasing doses, are called stochastic.
Beta radiation is a stream of electrons or positrons emitted by the nuclei of atoms of radioactive substances during radioactive decay. The maximum range in air is 1800 cm, and in living tissues - 2.5 cm. The ionizing ability of p-particles is lower, and the penetrating ability is higher than that of oc-particles, since they have a significantly smaller mass and have the same energy as a-particles have less charge.
Neutron radiation is a stream of neutrons that convert their energy in elastic and non-elastic interactions with atomic nuclei. During inelastic interactions, secondary radiation arises, which can consist of both charged particles and gamma quanta (gamma radiation). In elastic interactions, ordinary ionization of a substance is possible. The penetrating power of neutrons is high.
Water is the most widely used extinguishing agent. It has a significant heat capacity and a very high heat of evaporation (-2.22 kJ/g), due to which it has a strong cooling effect on the fire. The most significant disadvantages of water include its insufficient wetting (and, therefore, penetrating) ability when extinguishing fibrous materials (wood, cotton, etc.) and high mobility, leading to large losses of water and damage to surrounding objects. To overcome these disadvantages, surfactants (wetting agents) and viscosity-increasing substances (sodium carboxymethylcellulose) are added to water.
In explosive areas, radioisotope neutralizers are used, the action of which is based on the ionization of air by the alpha radiation of plutonium-239 and beta radiation of promethium-147. The penetrating ability of alpha particles in the air is several centimeters, so the use of an alpha source is safe for personnel.
Depending on the size of the droplets, the jets are droplet (droplet diameter > 0.4 mm), atomized (droplet diameter 0.2-0.4 mm) and finely atomized (fog-like, droplet diameter
When extinguishing with water jets, their penetrating ability is essential, which is determined by the pressure
The pressure of the water jet is determined experimentally by the speed of movement of the drops and the air flow they entrain. Penetration ability decreases with decreasing jet pressure and droplet size. When the droplet diameter is more than 0.8 mm, the penetrating ability does not depend on the jet pressure.
Radioactive isotopes emit various types of radiation invisible to the eye: a-rays (alpha rays), 3-rays (beta rays), rays (gamma rays) and neutrons. They are able to penetrate solid, liquid and gaseous bodies, and for different types of radiation the penetrating ability is not the same: rays have the greatest penetrating ability. In order to detain them, a layer of lead approximately 15 cm thick is needed.)