Explanation

The process of reducing neutron energy caused by scattering in the absence of obvious capture. The slowing down of fast neutrons is mainly caused by the elasticity collision between neutrons and moderators. The moderating ability of a substance is the average logarithmic energy drop of neutrons passing through the unit path when they move in the substance, which is equal to the product of the average logarithmic energy drop of neutron collisions and the macroscopic scattering cross-section of the substance towards neutrons. The former is inversely proportional to the number of collisions required to slow down fission neutron moderation to thermal neutrons, which does not indicate the scattering probability of matter to neutrons. The slowing ability provides the ability of matter to slow down neutrons, without considering the absorption of neutrons by matter. materials that can be used as moderators include hydrogen containing materials (ordinary water, heavy water, some organics and metal hydrides), beryllium (metals, oxides and carbide) and carbon (heavy water in the form of graphite has a small absorption cross section and is the best moderator. The average energy of fission neutrons is about 2MeV. In thermal neutron reactors, fission must be transferred to the thermal energy (0.025eV) range. The selection of suitable moderators for thermal neutron reactors must be based on the reactor type.

Classification