8. Neutron thermalization

In the field of slowing down, two approximations can be made in the treatment of neutron scattering by matter:

• the target nuclei can be considered immobile before the interaction (their kinetic energy due to thermal agitation is low compared to the kinetic energy of the neutron);

• neutrons interact with nuclei as if they were perfectly isolated (in reality, these nuclei are at the center of atoms bound together in molecular or crystalline systems).

Since thermal agitation corresponds to an energy of a fraction of an electron volt, and since the energies of chemical bonds are also of this order of magnitude, the domain of thermalization can be defined as that of neutron energies below a few electron volts.