Harm and protection of ray radiation in ray detection operation

Due to cracks and fractures in equipment pipeline welds, accident hazards are serious. For example, “pressure vessel safety technology” published by the Ministry of Labor’s Boiler and Pressure Vessel Safety magazine in June 1989 listed six pressure vessel explosion accidents and 164 deaths. Nearly 1,000 people were injured and poisoned. The direct economic losses amounted to 10 million yuan, and the indirect economic losses amounted to several hundred million yuan. The major cause of accidents was caused by weld quality problems. Radiographic inspection is an important technique for verifying the quality of metal butt welds. During the process of reconstructing and expanding the petrochemical industry, in order to ensure the quality of the welding operation of the construction project, effectively prevent the damage or leakage after the new installation or facility is put into operation, and ensure that the new installation and the new facility after the production can operate safely, the equipment must be The butt weld of the pipeline is examined by ray inspection. At present, ray detection is a good method to test the quality of welds.

The hazard of ionizing radiation to the human body is caused by radiation acting on the body beyond the allowable dose. Radiation hazards are divided into in vitro and in vivo hazards. In vitro hazards are caused by radiation penetrating into the body from outside the body. X-rays, gamma rays, and neutrons can cause injury. In vivo hazards are caused by swallowing, inhaling, or contacting with radioactive material, causing it to enter the body directly.

In radioactive materials, low-energy beta particles and alpha particles with very weak penetrating power can be prevented by the skin and do not cause serious damage to the body. However, if the alpha particles with large ionization ability invade the human body, serious injury will result.

The harmful effects of ionizing radiation on the body's cellular tissues are mainly to hinder and harm the functioning of cells and cause cell death. The degree of damage to human body caused by ionizing radiation is related to the radiation dose. The greater the dose, the greater the damage. However, different individuals or different organs have differences in radiosensitivity. Such individual differences are usually manifested when irradiated by 2.58×10-2C/kg or less, and most of the individuals may have mild radiation sickness. Reactions, while a few can be expressed as moderate damage. For sensitive organs, such as the eyes, liver, spleen, lymphocytes, bone marrow, etc., even if the skin is not harmed, it may cause serious damage.

Repeated exposure to allowable doses of radiation in the human body can also cause changes in the body's cells, resulting in excessive leukocytosis, opacity of the lens, dry skin, loss of hair, and endocrine disorders. Higher doses can cause bleeding, anemia and leukopenia, gastrointestinal ulcers, skin necrosis and ulcers. Under extremely high doses of radiation, it can cause three types of radiation damage.

The first is damage to the central nervous system and the brain system. Mainly manifested as weakness, fatigue, drowsiness, coma, tremors, paralysis, can die within 2 days. The second type of injury is gastrointestinal injury. Mainly manifested as nausea, vomiting, diarrhea, weakness and collapse, acute coma may occur after symptoms disappear, usually within 2 weeks of death. The third is the damage of the hematopoietic system. Nausea, vomiting, and diarrhea, but quickly improved, after about 2 to 3 weeks, hair loss, recurrent nosebleeds, and diarrhea reoccurred, causing extreme paralysis, usually dying after 2 to 6 weeks.

1 Radioactive sources that are usually exposed to radiation

Human beings live in a natural radiation environment. Some of the natural radiation factors from the cosmic rays outside the Earth and the Earth’s environment itself are transmitted through the air, drinking water, and complex food chains into the human body or external radiation. Harm human health.

2 Natural background radiation

In daily life and work, the human body cannot completely avoid radioactive radiation even if it does not engage in radioactive work. The sources of natural background radiation mainly include: (1) Cosmic rays. About 9.03×10-6C/kg per person per year; (2) Radiation from the earth's radioactive material. Each year about 2.58×10-5 C/kg per person; (3) Human body radioactive material. Rays such as C14, N16, P32, and H3 receive approximately 9.03×10-6 C/kg per person per year. The above three aspects are the basic components of natural background radiation, and the total dose is approximately 4.39×10-5 C/kg per person per year.

3 maximum allowable dose

The internationally stipulated maximum allowable dose standard is that during the lifetime of a person, no appreciable harm will occur even if the dose is irradiated for a long period of time. In China's Radiation Protection Regulations issued in 1974, the maximum allowable doses for internal and external radiation are shown in Table 1.
Table 1 Maximum allowable dose unit for internal and external exposure: Sv/a Irradiation site Occupational radioactivity Worker maximum allowable dose equivalent 1
Permitted dose of workers and residents in adjacent and nearby radioactive workplaces
Classification Organ Name First Class Whole Body, Gonad, Red Bone Marrow, Eye Crystal 5.0×10-2 5.0×10-3
The second type of skin, bone, thyroid 0.30 3.0×10-2
The third type of hand, forearm, sacrum 0.75 7.5×10-2
The fourth type of other organs 0.15 1.5×10-2
Note:
1 The values ​​listed in the table refer to the total dose equivalent of internal and external radiation, excluding natural background radiation and medical radiation.
The limit dose equivalent of the thyroid gland for persons under 216 is 1.5 x 10-2 Sv/a.

Since human tissues can be ionized when they are exposed to radiation, the radiation does not harm the human body when the radiation dose is lower than a certain value. If the human body is exposed to radiation, it can produce different degrees of damage. Therefore, the basic principle of radiation protection is to avoid radioactive substances or radiation polluting the environment and invade the human body, and take various measures to reduce the amount of radiation that humans receive from inside and outside. The basic measures to prevent ionizing radiation from harming the human body are: shorten the contact time, increase the distance, conduct screen protection, remote control, mechanized operation and personal protection, etc. to prevent radioactive substances from polluting the environment and invading the human body and reducing the radiation dose to the human body. For places engaged in radioactive work or in the presence of radioactive contaminants, the operators shall conduct systematic education and training on safety protection knowledge, establish and improve health protection systems and damage regulations, set up hazard signals, color standards, and alarm facilities. Specific protection methods are as follows:

1 shorten the time of exposure

That is time protection. When working on exposure to radiation, the cumulative dose of external exposure to the human body is proportional to the exposure time, which means that the exposure time is long and the cumulative dose received is greater. In order to reduce the dose of workers exposed to radiation, working hours should be shortened, unnecessary stays in radiation sites prohibited, work needs to be close to radioactive sources, and the work should be left immediately after completion of work, working under conditions with relatively high doses, and poor protection conditions. Next, in order to reduce the exposure time, it is possible to take turns in batches so as not to exceed the allowable dose for a long time.

2 Keep away from radioactive sources

That is distance protection. The radiation intensity of radioactive material is inversely proportional to the square of the distance, ie: I1/I2=d22/d12
Where: I1 - radiation intensity from the source distance d1, Bq;
I2 - radiation intensity at a distance d2 from the source, Bq.

It shows that the dose rate (dose received per unit time) received by the staff is inversely proportional to the square of the distance.

For example, a cobalt source of 1.0 x 107 Bq is located 10 cm away from it, and the generated gamma ray dose rate is the same as that of 1.0 x 105 Bq cobalt source at a dose equal to 1 m. Therefore, to increase the operating distance, the implementation of a remote control approach can achieve the purpose of protection.

3 Shield protection

That is, the human body or radiation source is shielded so as to separate the radiation from the human body. In places where radioactive work is performed, where radioactive sources are handled, and where radioactive materials are stored, the method of shielding is an important measure to reduce or eliminate the radiation hazard. The material and form of the shield are usually determined according to the nature and intensity of the radiation.

Shielding gamma ray is commonly used in lead, iron, cement, brick, stone, etc.; shielded beta ray is commonly used in organic glass, aluminum plate and so on. The shielding thickness of the shielding rays can be obtained through theoretical calculations. At the same time, the instrument can be used to determine the shielding safety range. Theoretical calculations can be obtained by referring to the formulas and calculation tables provided on pages 378 to 381 of Chemical Safety Technology (Note: Chemical Industry Press, 1984, Beijing First Edition) and other related materials. At present, the factory's theoretical calculation and measurement tasks are undertaken by the Occupational Disease Control Division of the plant.

At present, non-destructive testing of welds is usually carried out using X-rays or gamma rays. Some new, modified, and expanding devices are based on site constraints and interspersed within or adjacent to the periphery of the production device of the operating device. Therefore, ray detection is affected. The scope of personnel health protection work is often complex and changeable.

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