Accidents with ejection (threat of release) of radioactive substances
Among the technogenic sources of emergencies, radiation accidents represent the greatest danger in terms of the scale, severity of the damage and the duration of the impact of the damaging factors. The main problems of radiation safety are related to the development and operation of nuclear power facilities, as well as some other forms of peaceful and military use of nuclear energy. Waste of nuclear technologies is a significant danger. Accumulated volumes of spent nuclear fuel and high-level nuclear waste also pose a serious threat to the occurrence of large-scale radiation accidents.
Radioactivity is the ability of a number of chemical elements to spontaneously decay and emit invisible radiation.
E. Rezenford experimentally established (1899) that uranium salts emit rays of three types that differ in a different way in a magnetic field:
1) rays of the first type deviate in the same way as the flow of positively charged particles; they were called α-rays (these particles (the flux of the nuclei of helium atoms) emerge from the nucleus at a speed of 15,000-20,000 km/s, have very little ability to penetrate, air can travel from 2 to 9 cm in the air, from 0.02 to 0.06 mm, can be completely absorbed by a sheet of clean paper);
2) rays of the second type are usually deflected in the magnetic field in the same way as the flow of negatively charged particles, they were called β-rays (a note of electrons emitted from the nuclei at the speed of light, their ability to penetrate is high.) In the air, beta particles can pass distance up to 15 m, in water and biological tissue - up to 12 mm, in aluminum - up to 5 mm);
3) rays of the third type, which are not deflected by a magnetic field, were called gamma rays (gamma rays are electromagnetic radiation with a wavelength of 10-8 to 10 10 cm.) The penetrating power of gamma rays is very high. To weaken the gamma -radiation of radioactive cobalt in half, a slab of lead 1.6 cm thick or 10 cm thick concrete is needed.)
Any change in the irradiated object caused by ionizing radiation is called a radiation-induced effect. Radiation-induced effects can be both harmful and useful. The extreme example of the harmful effects of radiation is the radiation damage to the body as a result of excessive doses of ionizing radiation. At the same time, ionizing radiation is successfully used for the diagnosis and treatment of certain diseases.
The radioactive substance is one of the constituent components of the biosphere, which determines the radioactive background of the Earth.
There are five basic units for measuring radiation doses. Although some of them coincide in dimension, they bear a different meaning. Let us dwell in more detail on each of them.
1. Gray (Gr) - unit of the absorbed radiation dose in the SI system. 1 Gy is the absorbed dose of radiation at which an irradiated substance weighing 1 kg transmits the energy of ionizing radiation 1 J 1 Gy = 1 J/kg = 100 rad.
2. Rad - is an extra-system unit for the dose of radiation absorbed by the substance. 1 rad - dose of radiation per 1 kg of body weight, equivalent to energy in 0.01 Joule 1 rad = 0.01 Gy.
3. Baer (biological equivalent of X-ray) is an out-of-system unit for measuring the equivalent dose of radiation. 1 rem - dose of any kind of ionizing radiation, producing the same biological effect as the dose of X-rays or gamma rays in 1 P.
4. X-ray (P ) is an extrasystem exposure dose of radioactive irradiation by X-ray or gamma radiation, determined by their ionizing effect on dry atmospheric air. In transferring to SI 1, the X-ray is approximately 0.0098 Sv. 1 P = 1 Baer.
5. Sievert (Sv) is the unit of the equivalent radiation dose in the SI system. 1 Sv is the equivalent radiation dose at which:
- the absorbed radiation dose is 1 Gy;
- the emission quality factor is equal to one.
1 Sv = 1 J/kg = 100 rem.
A detailed study of the effect of the Earth's radiation background at a dose of 1-10 mSv per year, or 100-1000 mrem per year, did not reveal any changes in the state of human health, morbidity and life expectancy. However, an increased level of radioactivity is associated with a risk to human health. Natural sources of radiation can be divided into two groups, cosmic and terrestrial.
Radiation accident - loss of control of the source of ionizing radiation caused by equipment malfunction, improper actions of employees (personnel), natural disasters or other causes that could lead or resulted in exposure of people above the established norms or to radioactive pollution of the environment.
The measure of the ionizing effect of external radiation is the exposure dose (De), determined by the ionization of air. For the unit of exposure dose used in RSPS, x-rays are taken.The measure of the ionizing effect of internal exposure is absorbed dose. The unit of absorbed dose is gray (Gy).
To transfer the amount of energy absorbed in space (exposure dose) into the absorbed by soft tissues of the body, use the proportionality factor K = 0.877, i.e. 1 P = 0.877 rad .
The dose absorbed by the substance on the fourth day after receiving under the influence of physical and biological decay begins to move (exit) from the substance (organism). This dose is called a reversible dose. 50% of it goes for the first month, and the rest - for three months at a rate of 2.5% per day. In total, 90% of the absorbed dose leaves, 10% remains in the substance (body) as a residual dose. Basically, it is calcium, not excreted from bones.Forms, degree and depth of radiation damage developing in biological objects (including humans) under the influence of ionizing radiation (AI), depend on the amount of absorbed energy of the AI (dose).
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