Thermal Neutron Scattering and Transport in Methane at 20K

Abstract

A thermal neutron scattering kernel in methane has been suggested which takes into account the contributions from both phonon and libron exchange processes. The observed total neutron scattering cross-section can be explained at 20 K, when as many as fourteen libron exchange processes are considered in the thermal neutron scattering kernel along with phonon exchange processes upto two quanta. Using the suggested scattering kernel, thermal neutron transport under different conditions like time dependent, space dependent and steady state neutron spectra have been studied at 20 K. The results of these studies are quite different from other hydrogenous moderators like ice, etc. The production of intense beams of cold neutrons at 20 K and below indicate that normal methane is a better moderator for finite sizes of the assembly while heavy methane is a better source of cold neutrons for infinite sizes of the assembly as compared to other hydrogenous moderators.