Radioactive source classification

The classification of radioactive sources is related to their activity. Even low-energy radiation sources have the potential to harm humans. According to the State Council Decree 449 "Regulations on the Safety and Protection of Radioisotopes and Radiation Devices", with reference to the relevant provisions of the International Atomic Energy Agency, the radioactive sources are divided into I, I Class II, III, IV, V, the lower limit activity value of the source of class V is the exempt activity of the species (activity: the number of nuclear decay that occurs per unit time of radioactive material). Class I radioactive sources are extremely high-risk sources. Without protection, exposure to such sources can cause death within a few minutes to 1 hour; Class II radioactive sources are high-risk sources. Without protection, exposure to such sources for several hours Can cause death in a few days; Class III radioactive sources are dangerous sources. Without protection, exposure to such sources can cause sexual damage to people within a few hours, and exposure to a few days to several weeks can cause death; Class IV Radioactive sources are low-risk sources, which basically do not cause human-induced damage, but may cause recoverable temporary damage to people who have been exposed to these radioactive sources for a long time and close range; Class V radioactive sources are extremely low-risk sources, not May cause sexual damage to people.

Principles for exemption of radiation source and radiation device

According to the national standard GB13367-92 "Principles of Exemption Management for Radiation Sources and Practices", it can only be satisfied. Only one of the following requirements can be directly exempted, other circumstances require protective measures:

• Any practice where the annual risk of fatal cancer or severe genetic defects caused by its exposure is less than 1 × 10-7;

• In practice, the annual effective dose equivalent to the individual being irradiated is not more than 10μSv (the annual dose equivalent to skin irradiation is not more than 500μSv), and the collective dose equivalent burden caused by one year of practice is not more than 1 person · Sv;

• Radiation device with radiant energy less than 5keV;

• A radioactive substance that exists in a form that appears in nature without being treated to increase the concentration of nuclide. However, uranium and thorium mines are not included.

Personal dose limit

In the basic standard of radiological health protection in China, the limit of the dose equivalent of workers in the civil year is adopted as recommended by the ICRP (International Radiation Protection Committee). The annual dose equivalent of one year should not exceed 50mSv, and the annual dose equivalent of any one year of public exposure should be less than 5mSv. When continuously exposed to radiation for a long time, the annual dose equivalent limit of the whole year's exposure of individuals in the public should not be higher than 1mSv, and these limits do not include natural background exposure and medical exposure.

Examples to explain the role of protective clothing

Example 1: Reactor leak

Nuclear power plants, nuclear ships, etc. all have reactors, and nuclear events such as reactor leaks or pipeline ruptures occur below level 3, and a large amount of radioactive material leaks are scattered in the environment. Among the monitored nuclides, several of them are common nuclides for calculation. Set the limit value of the equivalent dose of the whole body uniform radiation dose to the emergency workers to 50mSv. Calculate and compare the time required to reach the dose equivalent annual limit of 50mSv with or without shielding.

According to the test results and internal test values ​​of protective clothing of Nanjing Nuclear Safety Technology Co., Ltd. (http://www.esoexp.com), the minimum shielding rate of the front chest, back, crotch and back brain is selected as a reference. 30keV γ-ray shielding rate value is 83.2%, 57.356keV γ-ray shielding rate value is 27.22%, 80.99keV γ-ray shielding rate value is 35.5%, 106keV γ-ray shielding rate value is 45.5%, 364keV γ-ray value The shielding rate is 5%.

According to the test results and internal test values ​​of traditional protective clothing, the minimum value of the shielding rate of the front chest, back, crotch, and back brain is selected as a reference. The gamma shielding rate of 30keV is 78.6%, and the gamma shielding rate of 57.356keV The value is 25.6%, the gamma shielding rate of 80.99keV is 27.5%, the gamma shielding rate of 106keV is 20%, and the gamma shielding rate of 364keV is 2%.

Nuclear power plant and nuclear ship maintenance personnel also need to wear personal radiation protection equipment.

There are strong radiations in many areas of nuclear power plants and nuclear ships. Although they are not as many as the types of nuclides released and the activity is large, they still need radiation protection. Before repairs are started, radiation measurements must be made in this area. Only within the allowable radiation dose range can maintenance personnel wear protective equipment and begin work.

Example 2: Nuclear explosion test

After the nuclear scientific research test, in order to detect the relevant data, it is necessary for the staff to enter a specific area, and radiation protection equipment is essential at this time. Among the monitored nuclides, several of them are common nuclides for calculation. It is considered that the limit value of the equivalent dose of the whole body uniform radiation dose for emergency workers is 50mSv. Comparing calculations with or without shielding to reach the dose equivalent annual limit of 50mSv

The time required.

According to the test results and internal test values ​​of protective clothing of Nanjing Nuclear Safety Technology Co., Ltd. (http://www.esoexp.com), the minimum shielding rate of the front chest, back, crotch and back brain is selected as a reference. The gamma shielding rate of 30keV is 83.2%, the gamma shielding rate of 140keV is 24.2%, the gamma shielding rate of 80.99keV is 35.5%, and the gamma shielding rate of 364keV is 5%.

According to the test results and internal test values ​​of traditional protective clothing, the minimum value of the shielding rate of the front chest, back, crotch and back brain is selected as a reference. The 30keV gamma shielding rate is 78%, and the 140keV gamma shielding rate is taken as The value is 10.64%, the gamma shielding rate of 80.99keV is 27.5%, and the gamma shielding rate of 364keV is 2%.

Example 3: Loss of radioactive source

At present, radiology technology has been widely used in various industries such as industry, agriculture, and medical treatment. In the process of its development, use and storage, once a safety accident occurs, it will endanger the ecological environment around the radioactive source and the lives and property of the broad masses of the people. If the class II radioactive source used for non-destructive testing is 170Tm, its γ-ray energy is 72keV, and its activity is 5 × 1013Bq. For some reason, the radioactive source is lost. In order to reduce the radiation hazard of the radioactive source to the public, it is necessary to retrieve the radioactive source in a short time. The nuclear emergency staff calculates the time required to reach the dose equivalent annual limit of 50mSv with or without shielding when the distance to the radioactive source is different.

According to the test results of Nanjing Nuclear Safety Technology Co., Ltd. (http: //www.esoexp..com) protective clothing and active protective clothing, the minimum value of the shielding rate of the front chest, back, crotch and back brain is selected as a reference. The 70keV γ-ray shielding rate is 52.5%; the active service protective clothing 70keV γ-ray shielding rate is 21.53%.

1) According to the calculation, the human body absorbed dose equivalent rate at 1m away from the 170Tm radiation source is 137mSv / h. At this time, the human body without protective clothing reaches the annual human dose equivalent limit of 50mSv at 21.9min; after wearing the protective clothing developed by our hospital, The equivalent rate of human absorbed dose is 65.075mSv / h, the human body reaches 50mSv of the human dose equivalent year limit at 46.1min; after wearing active protective clothing, the human body absorbed dose equivalent rate is 107.5mSv / h, the human body reaches the human dose equivalent year at 27.9min The limit is 50mSv.

2) According to the calculation, the human body absorbed dose equivalent rate is 45.5mSv / h at 2m away from the 170Tm radiation source. At this time, the human body without protective clothing reaches the human body dose equivalent annual limit of 50mSv at 1.1h; after wearing the protective clothing developed by our hospital The equivalent rate of human absorbed dose is 21.61mSv / h, and the human body reaches the annual limit of 50mSv of human dose equivalent in 2.32h. After wearing active protective clothing, the equivalent rate of human absorbed dose is 35.7mSv / h, and the human body reaches the human dose equivalent in 1.4h The annual limit is 50mSv.

3) According to calculation, the equivalent dose rate of human absorbed dose at 5m from the 170Tm radiation source is 8.73mSv / h. At this time, the human body without protective clothing reaches the annual limit of 50mSv of human dose equivalent at 5.73h; after wearing the protective clothing developed by our hospital The equivalent rate of the absorbed dose of the human body is 4.15mSv / h, and the human body reaches the annual limit of 50mSv of the dose equivalent of the human body at 12.048h; after wearing active protective clothing, the equivalent dose of the absorbed body is 6.85mSv / h, and the human body reaches the equivalent dose of the human body at 7.3h The annual limit is 50mSv.

4) According to calculation, the equivalent dose rate of human body absorbed dose at 10m away from the 170Tm radiation source is 2.426mSv / h. At this time, the person who does not wear protective clothing reaches the annual limit of 50mSv of human dose equivalent at 20.61h; after wearing the protective clothing developed by our hospital The equivalent rate of human absorbed dose is 1.152mSv / h, and the human body reaches the annual limit of human dose equivalent of 50mSv at 43.4h. After wearing active protective clothing, the equivalent rate of absorbed dose is 1.9037mSv / h, and the human body reaches the equivalent dose at 26.26h. The annual limit is 50mSv.

Case 4: General protection

For some radioactive sources used in normal scientific research, detection, and detection, nuclear workers should also pay attention to their own radiation protection in long-term practical operation projects. For example, the Co-57 source used in the Mössbauer spectrometer and petroleum survey equipment has a moderate activity of 3.5 × 1010 Bq and an average gamma ray energy of 130 keV. Under normal working conditions, the distance between the operator and the radiation source is 1 ~ 2 meters, and the time required to reach the dose equivalent annual limit of 50mSv under the shielding condition is calculated.

According to the internal test results of Nanjing Nuclear Safety Technology Co., Ltd. (http: //www.esoexp..com) protective clothing and traditional protective clothing, the minimum value of the shielding rate of the front chest, back, crotch and back brain is selected as a reference The γ-ray shielding rate of 130keV is 32.7%; the 70keV γ-ray shielding rate of active protective clothing is 13.26%.

1) According to the calculation, the equivalent dose rate of human absorbed dose at 1m away from the 57Co radiation source is 0.17mSv / h. At this time, the person without protective clothing reaches the annual limit of 50mSv of the human dose equivalent at 294.11h; after wearing the protective clothing developed by our hospital The equivalent rate of human absorbed dose is 0.1145mSv / h, and the human body reaches the annual limit of 50mSv of human dose equivalent at 436.68h; after wearing active protective clothing, the equivalent dose of human absorbed dose is 0.147458mSv / h, and the human body reaches the equivalent dose of human body at 339.08h The annual limit is 50mSv.

2) According to the calculation, the equivalent dose rate of the human body absorbed dose at 2m away from the 57Co radiation source is 0.0536mSv / h. At this time, the person without protective clothing reaches the annual limit of 50mSv of the human dose equivalent at 932.84h; after wearing the protective clothing developed by our hospital The equivalent rate of human absorbed dose is 0.036mSv / h, and the human body reaches the annual limit of 50mSv of human dose equivalent at 1388.89h; after wearing active protective clothing, the equivalent rate of human absorbed dose is 0.04649264mSv / h, and the human body reaches the equivalent dose of human body at 1075.44h The annual limit is 50mSv.

It can be seen from the above examples that radiation protective clothing plays an important role in low-level nuclear accidents in nuclear power plants and nuclear ship reactors, nuclear explosion tests, maintenance of nuclear power plants and nuclear ships, and low dose rate radiation environments. When a nuclear accident occurs, wearing protective clothing can earn more time for emergency personnel, thereby avoiding more property losses and personal injuries. In nuclear explosion tests, protective clothing during nuclear power plant and nuclear ship maintenance can effectively reduce the radiation dose of workers. In low-dose-rate radiation environments such as scientific research, medical treatment, and surveys, radiation protective clothing still plays an important role in the radiation safety of nuclear-related workers for a long time.