Rethermalization of neutrons in graphitebismuth systems

Abstract

Using plane geometry, with first block of media of finite thickness and the second block extending to infinity, we calculated the steady state neutron spectra at different space points in fourteen different systems of graphite-bismuth which involved medium discontinuity at 500°K, 300°K and 100°K for six cases, temperature discontinuity in bismuth for four cases and medium and temperature discontinuties together at the same time for four cases. The space variation of effective neutron temperature has been studied from the calculated spectra. Starting from an equilibrium distribution in the first medium (of finite thickness) we find that the equilibrium is disturbed as the interface is approached and in the second medium it is only at some distance from the interface that equilibrium is again re-established. Diffusion length of neutrons in graphite and bismuth at 500°K, 300°K and 100°K have also been reported.