1. Exposure to (1) the nuclear industry system: mining, smelting and processing of radioactive minerals, as well as the establishment and operation of nuclear reactors and nuclear power stations. (2) Production and use of radiation generators: gas pedals, medical and industrial and agricultural production of X-ray and 7-ray radiation sources.
(3) Processing, production and use of radionuclides: synthesis of nuclide compounds and drugs and their use in experimental research and diagnostics.
(4) Production of natural radionuclides in associated or ****ogenic mines: mining and processing of phosphorus fertilizers, rare earth mines, tungsten mines, etc.
(5) Production of natural radionuclides in associated or ****ogenic mines.
(5) Medical irradiation.
2. Commonly used units of ionizing radiation in the past, some of the commonly used special units of ionizing radiation, has been gradually replaced by the International System of Units (SI units), but the old and new units are still in use at the same time.
(1) radioactive activity (radioactivity): radioactive activity of the SI unit dedicated to the name of Beck (bec- querel), the symbol Bq, along with the dedicated unit of Curie (Curie). lBq = 2. 703X10-nCi.
(2) exposure (exposure, X): the amount of irradiation (X): the amount of exposure (X) is only used for X-rays, but at present the old and new units are still in use. X) is used only for X-rays or 7-rays, there is no SI unit moniker, retaining the use of the unit name for the Roentgen (Roentgen, R).
(3) absorbed dose (absorbed dose, D): indicates the amount of radiation energy absorbed by the irradiated medium, applicable to any type of ionizing radiation. Absorbed dose and irradiation amount of meaning is completely different, but under certain conditions can be converted. Absorbed dose of SI units dedicated to the name of Gray (Gray), the symbol Gy; the original use of units for the rad, the symbol rad. lGy = 100 rado
(4) dose equivalent (dose equivalent, H): in order to measure the biological effects of different types of ionizing radiation, the absorbed dose multiplied by a number of correction factors, that is, the dose equivalent (H), H = DQN. In the formula, D for the absorbed dose; Q for different radiation quality factor, or line quality coefficient, refers to the unit length of the medium, due to ionization collision and the loss of the average energy, the greater the value of Q, the stronger the relative biological effect; N is temporarily set at 1. Dose equivalent of the SI unit dedicated to the name of the Sivevert (Sivevert), the symbol Sv; the original use of the unit name of the rem (rem). lSv = 100remo, the original use of the unit name of the Rem. lSv=100remo
3. Modes of action and effects of ionizing radiation Ionizing radiation acts on the human body in two ways: by external irradiation and by internal irradiation. External exposure is characterized by the cessation of radiation effects as soon as the source of radiation is removed or kept away. Internal irradiation occurs when radionuclides enter the body through the respiratory tract, the digestive tract, the skin or by injection and then act on the body. The effect is negligible until the radionuclides are expelled from the body or undergo a metamorphosis of more than 10 half-lives.
The damage of ionizing radiation on the body is affected by both the radiation factor and the body.
(1) Ionizing radiation factors
1) Physical properties of radiation: the ionization density and penetration of radiation, is an important factor affecting the damage. For example, cx particle ionization density is greater, but the penetrating power is very weak, its main harm is to enter the human body after the internal irradiation, and the role of external radiation is very small; 卩粒子 ionization capacity is smaller than a, but high-energy 卩 particles have the ability to penetrate the skin surface; X-rays and 7-ray penetration is far stronger than the 卩 particles, in particular, high-energy X-rays or 7-rays, which can be penetrated to the deep tissue or the entire human body tissues, with a strong penetrating radiation effect. powerful penetrating radiation effect.
2) Dose and dose rate: The general rule between the dose of ionizing radiation and the biological effect is that the higher the dose, the stronger the biological effect, but not exactly a linear relationship. Dose rate is the amount of irradiation received by the body per unit of time, often expressed in Gy/d, Gy/h or Gy/min. In general, the dose rate is large, the effect is also large.
3) irradiation site: irradiation of different geometric conditions, so that all parts of the body to receive uneven irradiation, which affects the absorption dose. The strongest response to abdominal irradiation, followed by the pelvis, head and neck, chest and limbs.
4) irradiation area: the larger the irradiated area, the more obvious the effect. The same amount of irradiation, local irradiation is not obvious, if the whole body to receive irradiation area of 1/3, can produce obvious radiation effects.
(2) body factors: the higher the germline evolution, the more complex the body's organizational structure, the stronger the radiation susceptibility. The susceptibility of the tissue to radiation is directly proportional to the cell division activity, and inversely proportional to the degree of differentiation. Radiation sensitivity is also proportional to the volume of interphase chromosomes, i.e. to the DNA content of the cell. Cells with the ability to proliferate are in different cell cycles and have different radiosensitivities, with the highest sensitivity being during the DNA synthesis phase. The radiosensitivities of different types of cells, in descending order, are as follows: lymphocytes, proerythrocytes, myeloid cells, bone marrow megakaryocytes, spermatocytes, oocytes, glandular fossa cells of the jejunum and ileum, epithelial cells of the skin and organs, epithelial cells of the lens of the eye, chondrocytes, osteoblasts, vascular endothelial cells, adenohypophyseal cells, hepatocytes, tubular epithelial cells of the kidneys, neuroglia, neuronal cells, lung epithelial cells, muscle cells, and other cells that have the ability to proliferate. The cells of the lung epithelium, myocytes, connective tissue cells, and osteocytes.
4. Biological effects of ionizing radiation Ionizing radiation can be classified into stochastic effect and deterministic effect according to the dose-effect relationship. Stochastic effect refers to the incidence of radiation effects (rather than its severity) and dose-related, there is no dose threshold (dose threshold). There are mainly carcinogenic and hereditary effects. Deterministic effect means that the severity of radiation effect depends on the dose received, and there is a clear dose threshold, below the threshold will not see harmful effects, such as radioactive skin injury (radiation skin injury), radiation 'sexual fertility disorder (radiation induced fertility disturbance). Ionizing radiation can be divided into somatic and genetic effects according to the individual classification of the effects. Ionizing radiation is classified into somatic and genetic effects. Embryonic and fetal effects, which occur when the fetus is exposed to radiation in the womb, are a special type of somatic effect. Ionizing radiation according to the type of effect classification: can be divided into high-dose exposure of acute effects, low-dose long-term exposure of chronic effects, as well as long-term effects occurring after exposure to radiation.
Ionizing radiation can cause changes at the molecular level in living organisms, especially in biological macromolecules, such as nucleic acids, proteins (including enzymes), etc., causing them to undergo ionization, excitation, or breakage of chemical bonds, thus resulting in alterations in the structure and properties of biological macromolecules. This action occurs at the earliest, called direct action. In addition, inside and outside the cell contains a large number of water molecules, ray action on the water molecules, causing their ionization and excitation, the formation of chemically active products, such as excited state of the water molecules, hydrogen radicals, hydroxyl radical hydration electrons, etc., and then act on the biological macromolecules to make changes in this series of effects is called indirect action.
The result of these actions is cellular damage, especially DNA damage. Deterministic effects occur when a sufficient number of cells in an organ or tissue die or lose the ability to divide and reproduce as a result of damage. If somatic cells with altered structure and function retain their ability to reproduce, they may form mutant cell clones in the body, which may eventually cause cancer. When the damage occurs in the gonadal germ cells, it may cause genetic effects by transmitting incorrect genetic information to the offspring.