THE THERMAL NEUTRON SPECTRUM IN A FINITEMASS MEDIUM.

The distribution of neutrons at thermal energies in a monatomic Maxwellian gas is determined. Spectra are found in various mass media and for varying amounts of absorption by numerically solving Corngolds higher-order gas equation a result that is new. From the spectra obtained the average neutron velocity is found and the thermal diffusion length squared is calculated. Using this method and a neutron age from a moments method calculation, the migration area in selected real nuclides is determined. The deviations from Maxwellian of the thermal neutron spectra are used to determine the energy at which a neutron becomes thermal. This effective thermal transition energy, E, is found for media of various mass with varying amounts of absorption. The neutron thermal spectrum is found to be generally non-Maxwellian for values of the absorption parameter greater than 0.01.