Radiation shielding refers to a radiation protection technology that uses radiation and substances to reduce the radiation level of a certain area, thereby reducing people's exposure to radiation and radiation damage of materials, and is also a material protection measure.
In nuclear power plants, the main targets of radiation shielding are gamma rays (gamma photons) and neutrons. The gamma photons pass through the shield and are mainly attenuated or absorbed by the process through energy transfer, Compton scattering, and electron pair formation. The photoelectric effect is that the photon transmits all the energy to orbital electrons, which causes the electrons to escape from the shell and release them from the atoms. This plays a major role in the absorption of low-energy gamma photons (gamma photons with energy less than several hundred keV). Compton scattering is the collision of photons with free electrons, which transfers part of the energy to electrons, and changes their direction and energy at the same time. It plays a major role in reducing the energy of intermediate energy gamma photons (energy is between several hundred keV and several MeV). The electrons interact with the electric field of the gamma photons and the nucleus. The gamma photons are completely annihilated. The energy is converted into the mass and kinetic energy of a pair of positive and negative electrons and the kinetic energy of the recoil nucleus. It is used to absorb high-energy gamma photons (energy greater than a few meV). main effect.
Determine the radiation level of the observation point The determination of the radiation level at each observation point is related to the purpose of shielding. For the health of the staff, different radiation levels should be determined according to the frequency and time of the staff approaching the radiation source, and the area should be shielded (see Nuclear Power Plant Radiation Division). In order to prevent the irradiation damage of the equipment, prevent the activation of the material and maintain the stability of the shield, the radiation level should be determined according to the characteristics of the material and the use requirements.