By 1965, 1,130 unstable nuclides had been discovered. An unstable nucleus can spontaneously decay into another unstable nuclides (or stable elements) that simultaneously emit radiation during the decay process. This property of radionuclides has been widely used in the fields of industry, agriculture, medicine, and national defense. In today's world, nuclear technology competition and energy crisis have intensified, accelerating the process of nuclear energy utilization. Nuclear radiation is becoming more and more serious to the atmosphere and the environment. People are very concerned about this. Now I will talk about my own shallow understanding of the sources of radioactivity, the dangers of radioactivity, and the prevention and control of radioactivity.
First, the source of radioactivity
(1) Natural radioactive sources in nature
Uranium exists in nature based radium, thorium and actinide series of three radiation. The starting nuclides of the uranium radium system are uranium 238, which has become a stable elemental lead after 15 generations of decay. The fading deformation type is: 23893U→23490Tn...→22688Ra→22386Rn...→20782Pb. After 8 generations, it turns into a stable elemental lead. The decay deformation formula is: Rn→RaA→RaB→RaC...→20782Pb.
Radionuclides emit a variety of different rays during the decay process. There are mainly alpha, beta, gamma rays and electron capture.
Alpha decay, the unstable nucleus spontaneously emits alpha particles and becomes another nucleus, the ruthenium (42He) nucleus, consisting of two neutrons, two protons, with two positive charges. After the alpha nucleus decays, the atomic weight of the newly formed nuclides is reduced by 4 and the atomic number is decreased by 2. If 22688Ra emits alpha particles, it becomes 22286Rn. The alpha ray penetration ability is very weak and a piece of paper can block it.
Beta decay, when the radionuclide decays, beta particles are released, and beta particles are electrons. Before and after β decay, the mass numbers of the parent and daughter nuclei are unchanged, but the atomic number of the daughter nuclide is higher than that of the parent. For example, 21438Bi (RaC) becomes 21484Po(RaC') after β decay, and the β-ray has stronger penetrating ability than α-ray, but can be blocked by 5mm lead plate.
Electron capture refers to the atomic nucleus capturing an orbital electron outside the nucleus, making a proton in the nucleus a neutron, so the atomic nucleus of the nucleus produced has one less atomic number than the parent, and the mass number is unchanged. For example, 4019K becomes 4018Ar after electron capture.
In the process of decay, radionuclides are generally accompanied by gamma ray emission, which is an electromagnetic wave with a very short wavelength and no charge. It has a strong penetrating power and requires a 10cm thick lead plate to block it.
(2) Distribution of natural radioactive materials
Due to the different regions, the distribution of various natural radionuclides in the environment varies greatly. Radioactive elements are high in some mines, especially in uranium mines and volcanic immersed rocks.
Natural radionuclides in soil and rock are the main sources of radionuclides in the environment. Uranium is 2.8 μg/g in soil and 1 μg/g in rock; Ra (Radium) is 1×10-6 μg/g in soil and 8×10-3 μg/g in rock. Different soils and rocks have different contents. The content of radionuclides in igneous rocks is higher than that of sedimentary rocks and limestone is the lowest.
The concentration of natural U in river water is generally 0.3 to 10 μg/L, and the concentration of Ra is generally 0.37 to 37×10-2 Bq/L.
The concentration of Ra in the atmosphere on the land averaged 4.44×10-3 Bq/L, and the concentration of Rn over the ocean was about 3.7×10-5 Bq/L.
The Rn concentration in the air in different buildings is also different. For example, the rural soil house is 33.5×3.7×10-4Bq/L, and the cement floor tile house is 38.8×3.7×10-4Bq/L. In addition, foods such as soybeans, flour, milk, beef, vegetables, etc. contain radioactive substances to varying degrees.
(3) Artificial radioactive sources
With the acceleration of the utilization of nuclear energy, the pollution of artificial radiation sources to the atmosphere and the environment has become increasingly serious.
1. Atmospheric nuclear weapons explosions, underground nuclear explosions contain nuclear fuel, radioactive aerosols and radioactive sediments that induce radioactive and nuclear fission products diffuse into the atmosphere or fall to land, rivers and lakes due to their own weight. Radioactive materials and induced radioactive products produced by nuclear explosions have more than 200 radioisotopes of dozens of elements. Since 1945, the world's environment has been the main source of artificial radioactive contamination. The United States and the former Soviet Union have carried out a series of nuclear weapons tests and underground nuclear explosion tests in the atmosphere.
2. The pollution of the environment and the atmosphere of nuclear power plants and reactors that are normally carried out is mainly radioactive waste gas and waste enthalpy. The main radioactive materials emitted are 85Kr and 140Ba. By the year 2000, the total installed capacity of nuclear power in the world will reach 1030~1652GW(e), accounting for 50% of the total power generation. It can be seen that radionuclides are increasingly polluting the atmosphere and the environment.
The radioactive materials released by nuclear accidents are even more shocking. In October 1957, the Wentzkel reactor accident in the United Kingdom released a radionuclide 131I of about 740 TBq to the environment, accompanied by the release of nuclides such as 106Ru. The explosion of the Chernobyl nuclear power plant in the former Soviet Union in April 1986 caused serious pollution in the Eastern and Northern European environments and had varying degrees of impact on the entire northern hemisphere.
3. The pollution of the environment and the atmosphere during the mining process of the mine, especially the uranium mine, mainly comes from the “four wastes†(ie waste, waste gas, waste water, waste). For example, a mining method is 3m high, with an area of ​​200m 2 , and 1000t ore is deposited with a grade of 0.1%. The calculated helium production is about 3.0Bq/(st). After 10min, Rn179.82× can be produced. 10Bq, other mining methods also produce Rn to varying degrees and release into the air. In addition, the radioactive materials in waste water, waste water and waste seep into the ground, flow into rivers and streams, and spread to the atmosphere around the mine. The “four wastes†produced in the production of uranium water smelting plants have higher radioactive concentrations, and the atmosphere and the environment. The pollution is more serious. In essence, the uranium mine is a huge source of radiation.
4. Radiological diagnosis. With the development of nuclear science, radioisotopes are widely used in the medical field. It not only causes radioactive pollution to the environment, but also causes direct damage to the human body and even has a genetic impact.
Second, the danger of radioactivity
Radioactive materials in the atmosphere and the environment can enter the human body through the respiratory tract, digestive tract, skin, direct irradiation, genetics, etc., and some radionuclides enter the biological cycle and enter the human body through the food chain. The pathway for radionuclides and their decay products to enter the human body is shown in Figure 1.
After the radionuclide enters the human body, it has the characteristics of constant decay and emits radiation, as well as the direct radiation of the radioactive environment and radioactive diagnosis to the human body, namely internal and external irradiation, which causes the body tissues to lose normal physiological functions and cause tissue damage. damage.
Among them, the hazard is the most significant. Radon is the decay product of radium, and radium is the decay product of uranium.
From the radium A, after eight generations of decay, the stable elemental lead is formed. The first four generations, from RaA to RaC', have a short half-life and are called short-lived daughters.氡 is a colorless, odorless, odorless and transparent, liquid at -65 ° C, from liquid to gas at -17 ° C, the weight of gaseous Rn is 9.37g / L, the weight of liquid helium is 5.7 g/mm 3. The chemical nature of hydrazine is not active and generally does not participate in chemical reactions. Soluble in water, oil, organic solvents, the solubility in fat is 125 times in water. It can also be adsorbed by solid matter, and the ruthenium adsorbed on the solid surface forms an intractable radioactive film.
Figure 1 Schematic diagram of radionuclides and decay products entering the human body
As mentioned above, 氡 and its daughters have three types of decay modes: α, β, and γ. The characteristics of the three kinds of decay are different, and the degree of harm to the human body is different. Among them, the internal radiation of α-ray is the most harmful, because its short range, a piece of paper can block. It can be concentrated in a small area of ​​the human body for intense internal illumination, so that a small range of body tissue can withstand highly concentrated radiant energy and cause damage. For example, the range of alpha particles in the respiratory organs can bombard the nucleus of the basal cells of the bronchial epithelium, causing serious respiratory diseases and even lung cancer.
The harm of radiation to the human body comes not only from the internal irradiation of alpha particles, but also from the external irradiation of β, γ and other rays.
In radiation protection, which measures the extent of the effect of radiation on a substance, the concept of absorbed dose is quoted and is indicated by "D".
In the middle
- is the average mass of a substance in a voxel given by radiation, J;
Dm - the mass of the substance in the volume element, kg.
In addition, the concept of "dose equivalent" is also quoted and is indicated by "H".
H=DQN
Q-quality factor in the formula;
N—the product of any other correction factor.
According to relevant information, young women have a 9-fold increase in the risk of developing Downî„‹s syndrome in children after being diagnosed with radiation (0.7 to 5 rad) before pregnancy. Low doses of radiation are harmful to human fetuses.
In addition, radioactive radiation can induce carcinogenesis. There are two main hypotheses: "One is radiation-induced somatic mutation, which causes normal cells to transform into malignant cells. Second, radiation can change the environment of cells, thus contributing to the virus. Replication and virus-induced malignant lesions.
In addition to carcinogenic effects, late effects of radiation include aplastic anemia, shortened lifespan, cataracts, and abnormal retinal development.
Things are always divided into two. In addition to the harm to the human body, radioactive radiation is also beneficial to human aspects, such as radioactive detection and radioactive treatment of tumors. The key lies in how humans apply correctly, resolutely prevent and control radioactive hazards that are harmful to human beings, and make nuclear science continue to develop in the direction of benefiting humanity.
Third, the prevention and control of radioactivity
The prevention and control of radioactive pollution is an important issue related to the protection of the environment, the protection of people's health, and the promotion of social material and spiritual development. It has important practical significance and far-reaching historical significance.
Prevention and treatment should be based on both prevention and treatment, and treat both the symptoms and the root causes, with "defense" as the mainstay, and work hard on the word "governance". This makes the space and environment we rely on to be cleaner and more beautiful. This should be the common goal of all mankind.
(1) Effective control of the precipitation of sputum and daughters
For uranium mines, effective control of the precipitation of radon and its daughters is critical. As far as technical conditions are concerned, the use of extraction ventilation in mines is not good. Due to the extraction ventilation, the wellbore, stope and diverticulum are in a negative pressure state, and the air pressure in the pores of the ore is higher than the air pressure in the tunnel, the stope and the diverticulum, and the suction effect due to the decrease of the gas pressure, The rafts and daughters are separated from the ore into the mine space as the air flows. In the case of press-in ventilation, the air pressure in the well is larger than the air pressure in the rock, and the infiltrated air infiltrates into the pores of the rock. On the one hand, it dilutes the concentration of radon in the pores of the rock, and on the other hand changes the pressure gradient in the rock. The diffusion velocity of the tunnel to the well is constrained, and the air radon concentration in the tunnel is significantly reduced. The relevant data show that if the negative pressure of 573.7Pa is used, it will cause the amount of strontium to increase by 3 times, while the positive pressure of 573.7Pa will cause the amount of strontium to fall by more than 60%.
In addition, minimize the exposed surface of the ore and choose the best mining method. The filling method is not only suitable for the characteristics of small scale of uranium deposit, discontinuity of ore body, large change of grade, but also beneficial to control the precipitation of strontium. It is strictly forbidden to open up the veins.
In the process of crushing, grinding, screening and other processes in the uranium hydrometallurgical plant, a large amount of radioactive dust will be generated. Wet operation should be adopted, and a sealing cover should be installed on each equipment to enhance ventilation and exhaust dust removal.
(2) Effective treatment of radioactive industrial wastewater
With the development of the atomic energy industry, the amount of radioactive waste water generated is also increasing. The treatment of radioactive wastewater plays an important role in the prevention and control of radioactive pollution. At present, there are about one-third of nuclear power plants in the world, and their cooling water is discharged into the sea, lakes and land. This is only a negative treatment method and is not conducive to the protection of the global environment.
The United States has developed a new process for the treatment of low-level radioactive waste water, which is to re-use radioactive wastewater after coagulation and ion exchange treatment. It is a new way to supplement the lack of water resources and is conducive to the protection of the global environment.
(3) Personal protection
Workers in radioactive places wear high-efficiency dust masks; remove surface pollution, go to work, get off work; fully improve work efficiency and shorten working hours; do not eat, do not smoke, work skin rupture, do not work in radioactive places; To isolate the operator from the sputum-containing air; unless it is absolutely necessary for health, no one should be exposed to any amount of radiation.
(4) Fundamentally preventing and controlling
Conduct a comprehensive investigation of radioactive mines and tailings dams that have been decommissioned or will be decommissioned. Where conditions permit, it is necessary to resolutely return vegetation to the fields. It is strictly forbidden to mine and cure the soil; vigorously promote the technology of leaching mining and drilling and leaching. Because it does not require ore transfer, no water smelting process, no tailings dam, no waste. It is a combination of mining, selection and smelting, and has broad prospects for development; the selection of suitable formations for high-level radioactive waste, the construction of a final repository in the ground for hundreds of meters or more, and the use of the formation as a barrier to contain radioactive waste. . The radionuclides that are kept out of the waste can decay to a harmless level before they sneak into the biosphere; vigorously carry out comprehensive utilization of radioactive waste, such as nuclear batteries, illumination sources, and medical special energy.
Because I have not much research on radiology and radiology, I have only been practicing for more than 30 years in my own uranium mine and later radioactive mining professional teaching work, and I have read some shallow understandings and experiences about this offering. Inevitably, readers are urged to criticize.
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