Neutrons, Thermalization of

the last stage of the moderation of neutrons in various mediums, in which the role of chemical bonding and the thermal motion of the atoms of the medium become essential.

When the kinetic energy of neutrons is reduced to values less than 1 electron volt, the neutron velocity becomes comparable to the velocity of thermal motion of atoms and molecules. Energy exchange arises between these species and the neutrons, leading to the establishment of an equilibrium Maxwellian velocity distribution of the neutrons. However, because of several factors, such as the motion and binding of atoms, absorption, and the finite size of the system, the energy spectra of neutrons in moderators differ from the equilibrium spectra. The study of the thermaliza-tion of neutrons is required for the calculation and prediction of the behavior of thermal reactors. Research in this area has been the source of new methods for the study of the physics of solids and liquids.