Classification of radioactive sources The classification of radioactive sources is related to their activity. Even low energy ray sources have the potential to harm the human body. According to the stipulations of the State Council's Decree No. 449 “Safety and Protection of Radioisotope and Radioactive Devices,” and in accordance with the relevant provisions of the International Atomic Energy Agency, radioactive sources are divided into high-low and low-level sources according to the degree of potential harm of radioactive sources to human health and the environment. Category II, III, IV, and V, the lower activity value of the category V source is the exempt activity of this species (activity: number of nuclear decays per unit time of radioactive material). Class I radioactive sources are extremely high risk sources. In the absence of protection, exposure to such sources can cause death in a matter of minutes to an hour. Class II sources are high risk sources. Without protection, exposure to such sources takes a few hours. It can cause death in a few days. Class III sources are dangerous sources. If there is no protection, it can cause permanent damage to people within hours of exposure to such sources. It can also cause death in a few days to several weeks. Category IV Radioactive sources are low-risk sources that do not cause permanent damage to humans, but may cause temporary damage that can be rehabilitated to people who have been exposed to these sources for prolonged periods of time. V-type radioactive sources are extremely low-risk sources. May cause permanent damage to people.
The principle of radiation source and radiation device exemption can only be satisfied according to the national standard GB13367-92 "Regulations on exemption management of radiation sources and practices". One of the following requirements can be directly waived. In other cases, protective measures are required:
• Any practice in which the annual risk of fatal cancer or severe genetic defects caused by its irradiation is lower than 1 × 10-7;
• The annual effective dose equivalent to the irradiated individual is not greater than 10 μSv (the annual dose equivalent to skin irradiation is not greater than 500 μSv), and the collective dose equivalent burden generated by one year practice is not more than 1 person·Sv;
• Radiation devices with a radiant energy below 5 keV;
• Exist in forms that occur in nature, without the radioactive material being treated to increase the concentration of nuclide. However, it does not include uranium or antimony ore.
Personal Dose Limits In the basic standards for radiological protection in China, the limits of the dose equivalents for the working people in the civil year are set by ICRP (International Radiological Protection Committee) recommended limits. To prevent random effects, radioactive workers are subject to uniform body The annual dose equivalent for any year during irradiation should not exceed 50 mSv, and the annual dose equivalent of an individual in the public for any one year should be less than 5 mSv. In the long-term continuous exposure to radiation, the annual dose equivalent limit of annual exposure to systemic exposure of an individual in the public should not exceed 1 mSv, and these limitations do not include natural background radiation and medical radiation.
For example, explain the role of protective clothing Example 1: Reactor leakage events Nuclear power plants, nuclear ships, and so on all have reactors, nuclear reactors with leakage or pipeline rupture below the level of the three nuclear events, a large number of radioactive materials leaked in the environment. Among the monitored nuclides, several of these nuclides are listed as common nuclides for calculation. Set the emergency personnel to receive uniform dose equivalent limit value of 50mSv. Calculate the time required to reach a dose limit of 50mSv for the year under non-shielded conditions.
Based on the test results and internal test values of Nanjing Nuclear Safety Technology Co., Ltd. (http://.com) protective clothing, the minimum screening rate of the front chest, back, ankle, and hindbrain was selected as a reference, and a 30 keV gamma ray was selected as a reference. The screening rate is 83.2%, the gamma ray shielding rate of 57.356 keV is 27.22%, the gamma ray shielding rate of 80.99 keV is 35.5%, the shielding rate of 106 keV is 45.5%, and the gamma ray shielding rate is 364 keV 5%.
According to the traditional protective clothing test results and internal test values, the minimum shielding rate of the front chest, back, ankle, and hindbrain is selected as a reference. The 30 keV gamma ray shielding rate is 78.6%, and the γ-ray shielding rate is 57.356 keV. The value of 25.6%, the gamma ray shielding rate of 80.99keV is 27.5%, the shielding rate of 106keV is 20%, and the shielding rate of 364keV is 2%.
Nuclear power station, nuclear ship maintenance workers also need to wear personal radiation protection equipment.
There are strong ray radiation in many areas of nuclear power plants and nuclear warships. Although there are not many types of radionuclides emitted during reactor leakage events and they have large activity, they still need radiation protection. Before the start of maintenance work, radiation measurements must be taken in this area. Only within the allowable radiation dose range, can maintenance personnel wear protective equipment to begin operations.
Example 2: Nuclear Explosion Test After nuclear research and testing, in order to detect relevant data, workers need to enter a specific area, and radiation protection equipment is indispensable at this time. Among the monitored nuclides, several of these nuclides are listed as common nuclides for calculation. It is believed that the average equivalent dose limit for emergency personnel in the rescue work is 50 mSv. Calculate whether to reach the equivalent dose limit of 50mSv with or without shielding
The time required.
Based on the test results and internal test values of Nanjing Nuclear Safety Technology Co., Ltd. (http://.com) protective clothing, the minimum screening rate of the front chest, back, ankle, and hindbrain was selected as a reference, and a 30 keV gamma ray was selected as a reference. The shielding ratio is 83.2%, the gamma ray shielding rate of 140keV is 24.2%, the gamma ray shielding rate of 80.99keV is 35.5%, and the shielding rate of 364keV is 5%.
According to the traditional protective clothing test results and internal test values, the minimum screening rate of the front chest, back, ankle and hindbrain is selected as a reference. The 30 keV gamma ray shielding rate is 78%, and the 140 keV gamma ray shielding rate is taken as the value. The gamma ray shielding rate of 10.64%, 80.99keV was 27.5%, and the shielding rate of 364keV was 2%.
Example 3: Loss of radioactive sources At present, radiation technology has been widely used in industries such as industry, agriculture, and medical care. In the course of its development, use, and storage, once a security accident occurs, the ecological environment around the radioactive sources and the safety of life and property of the broad masses of people will be endangered. If used for non-destructive testing Class II radioactive source 170Tm, its gamma ray energy 72keV, activity 5 × 1013Bq. For some reason, the radioactive source is lost. In order to reduce the radioactive harm of the radioactive source to the public, it is necessary to recover the radioactive source within a short time. Nuclear emergency workers calculate the time required to reach a dose equivalent annual limit of 50 mSv in the presence or absence of shielding when they are different from the source.
According to the test results of Nanjing Nuclear Energy Technology Co., Ltd. (http://.com) protective clothing and active protective clothing, the minimum screening rate of the front chest, back, ankle, and hindbrain is used as a reference, and the 70 keV gamma ray is used as a reference. The screening rate was 52.5%; the protective gamma-ray shielding rate of 70keV in active duty was 21.53%.
1) According to the calculation of the body absorbed dose equivalent rate at 1m from the 170Tm radioactive source at 137mSv/h, at this time, the human body does not wear protective clothing to reach the human dose equivalent year limit of 50mSv at 21.9min; after putting on the protective clothing developed by our institute, The body absorbed dose equivalent rate is 65.075mSv/h, and the human body reaches the human dose equivalent annual limit of 50mSv in 46.1 minutes. After wearing active protective clothing, the body absorbed dose equivalent rate is 107.5mSv/h, and the human body reaches the human dose equivalent year at 27.9min. Limit 50mSv.
2) According to the calculation, the body absorbed dose equivalent rate at 2m from the 170Tm radioactive source is 45.5mSv/h. At this time, the human body does not wear protective clothing and reaches the human dose equivalent annual limit of 50mSv at 1.1h; after putting on the protective clothing developed by our hospital The body absorbed dose equivalent rate is 21.61mSv/h, the human body reaches the human dose equivalent annual limit of 50mSv in 2.32h; after putting on active protective clothing, the body absorbed dose equivalent rate is 35.7mSv/h, and the human body reaches the human body dose equivalent at 1.4h. Year limit 50mSv.
3) According to the calculation, the body absorbed dose equivalent rate at a distance of 5m from the 170Tm radioactive source is 8.73mSv/h. At this time, the human body does not wear protective clothing and reaches the human dose equivalent annual limit of 50mSv at 5.73h; after putting on the protective clothing developed by our hospital The body absorbed dose equivalent rate is 4.15mSv/h, and the human body reaches the human dose equivalent annual limit of 50mSv at 12.048h. After wearing active protective clothing, the body absorbed dose equivalent rate is 6.85mSv/h, and the human body reaches the human body dose equivalent at 7.3h. Year limit 50mSv.
4) According to the calculation of the human body absorbed dose equivalent rate at a distance of 10m from a 170Tm radioactive source of 2.426mSv/h, at this time the human body does not wear protective clothing at 20.61h to reach the human dose equivalent annual limit of 50mSv; after putting on the protective clothing developed by our hospital The body absorbed dose equivalent rate is 1.152mSv/h, and the human body reaches the human dose equivalent annual limit of 50mSv at 43.4h. After wearing active protective clothing, the body absorbed dose equivalent rate is 1.9037mSv/h, and the human body reaches the human body dose equivalent at 26.26h. Year limit 50mSv.
Example 4: Conventional Protection For some radioactive sources used for normal scientific research, detection, detection, etc., nuclear workers should also pay attention to their own radiation protection work during long-term practical operation. For example, the Co-57 source used in the Mössbauer spectrometer and the oil exploration equipment has a moderate activity of 3.5×1010 Bq and an average γ-ray energy of 130 keV. Under normal working conditions, the distance from the radioactive source to the operator is 1 to 2 meters. Calculate the time required to reach the dose-equivalent annual limit of 50 mSv with or without shielding.
According to the internal test results of Nanjing Nuclear Energy Technology Co., Ltd. (http://.com) protective clothing and traditional protective clothing, the minimum screening rate of the thorax, back, ankle, and hindbrain was selected as a reference, and the gamma of 130keV was used as a reference. The ray screening rate was 32.7%; the active gamma ray shielding rate of 70keV was 13.26%.
1) According to the calculation of the human body absorbed dose equivalent rate at 1m from the 57Co source 0.17mSv/h, at this time the human body does not wear protective clothing at 294.11h to reach the human dose equivalent annual limit of 50mSv; after putting on the protective clothing developed by our hospital The body absorbed dose equivalent rate is 0.1145mSv/h, and the human body reaches the human dose equivalent annual limit of 50mSv at 436.68h. After wearing active protective clothing, the body absorbed dose equivalent rate is 0.147458mSv/h, and the human body reaches the human body dose equivalent at 339.08h. Year limit 50mSv.
2) According to the calculation of the human body absorbed dose equivalent rate at a distance of 2m from the 57Co source at 0.0536mSv/h, the human body does not wear protective clothing at the time of 932.84h reaching the human dose equivalent annual limit of 50mSv; after putting on the protective clothing developed by our institute The body absorbed dose equivalent rate is 0.036mSv/h, the human body reaches the human dose equivalent year limit of 50mSv at 1388.89h; after putting on active protective clothing, the body absorbed dose equivalent rate is 0.04649264mSv/h, and the human body reaches the human body dose equivalent at 1075.44h. Year limit 50mSv.
From the above examples, it can be seen that radiation protective clothing plays an important role in the nuclear accidents of nuclear power plants, nuclear ship reactors, nuclear explosion tests, nuclear power plant, nuclear ship overhaul and low dose rate radiation environment. In the event of a nuclear accident, wearing protective clothing can allow more time for rescue personnel to avoid further property damage and personal injury. Nuclear explosion test, protective clothing for nuclear power stations and nuclear ships can effectively reduce the radiation dose of workers. In the low-dose-rate radiation environment such as scientific research, medical treatment, and surveying, radiation protective clothing still plays an important role in the long-term radiation safety of nuclear-related workers.
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