The monatomic gas model for thermal neutron distributions in a physical moderator

Abstract

Comparison of infinite medium spectra of monatomic gases with varying ratios of atomic mass to neutron mass has been made and shows similarity of the spectra for low absorption and disparity for high absorption. Spectra of the scalar flux and the neutron current in large geometry also have been computed and used to obtain the thermal neutron diffusion length of the monatomic gas. The possibility of duplicating the scalar flux and the diffusion length of a physical moderator by means of a monatomic gas of suitable mass ratio is emphasized. A model of this type which reproduces the thermal neutron distribution in light water is obtained and the variation with temperature of the diffusion length of the model is compared with experiment.