The radiation associated with the radiation source shield includes: (a) The radiation source has a useful beam. (b) Leakage radiation from a housing assembled through a radiation source, which is a non-useful harness. (c) Scattered radiation, ie, scattered radiation from objects, patients, device components, and building walls that are directly illuminated by useful and leaky radiation. (d) Sky-scattered radiation, that is, radiation that passes through the top of a shielded room (mainly useful and leakage radiation) interacts with the air above the top of the shielded room, and is scattered to the shielded outdoor ambient area. (e) Side-scattered radiation, that is, the radiation that the radiation source hits the top of the shielded room is at a certain distance from the outside of the roof shield. (f) When the radiation energy is high (such as proton therapy), the useful beam and the leaked radiation directly illuminate the neutrons generated by the nuclear reaction on the material and the associated radiation, which is the associated secondary radiation.
Nuclear power plant shields should have the following characteristics: 1 high density, can effectively absorb primary gamma and secondary gamma rays, but also can slow down the fast neutrons through inelastic scattering; 2 contains enough hydrogen, can be effective Slow down neutrons below the inelastic scattering threshold to thermal neutrons; 3 must have sufficient mechanical strength, mechanical stability, thermal stability, and chemical stability; 4 be inexpensive and easy to process and build. Only use a few materials in combination to meet these requirements. The shielding materials commonly used in nuclear power plants are steel, water, concrete (including concrete containing crystallized water or boron and heavy metal aggregates), and lead or boron-containing plastics are also used in local areas.