Neutron shielding mechanism of radiation-shielding materials

The type of interaction between neutrons and matter depends primarily on neutron energy. Based on energy levels, neutrons are categorized into three groups: slow neutrons (energy < 5 keV), intermediate-energy neutrons (5–100 keV), and fast neutrons (0.1–500 MeV); notably, slow neutrons with energies below 1 eV (typically 0.025 eV) are also referred to as thermal neutrons. Interactions between these neutrons and atomic nuclei generally fall into two categories-scattering and absorption-with scattering further subdivided into elastic and inelastic scattering. Absorption is the dominant interaction mode for slow neutrons, whereas elastic scattering predominates for intermediate-energy and fast neutrons; however, inelastic scattering becomes the primary interaction mode for fast neutrons with energies exceeding 10 MeV.

With the exception of elastic scattering, all the aforementioned neutron-matter interactions generate secondary radiation, making radiation protection critically important. Fast neutrons are the type most frequently encountered in practical applications; their interaction with matter involves initial scattering and moderation, followed by the absorption of slow neutrons, which results in the emission of charged particles or gamma rays. Due to limitations regarding the thickness of protective gear, neutron radiation suits are generally effective only against low- and intermediate-energy neutrons.