Asymptotic Distribution of Thermal Neutron Flux in an Infinite Medium of Beryllium Containing a Constant Plane Source

Abstract

The asymptotic energy spectrum of thermal neutrons in an infinite medium of beryllium was calculated for 300, 200, and 100 deg K, for a constant plane source of neutrons at the midplane. The techniques of multigroup diffusion theory were applied, using Nelkin's first order scattering kernel for Be, and the energy-dependent transport mean free path, lambda /sub tr/ (E), calculated by Bhandari. Because of the violent variation of lambda /sub tr/ in the vicinity of the Bragg cutoff energy, for the lower moderator temperatures the calculate flux spectrum is quite different from the Maxwellian. At 300 deg K the deviation from the Maxwellian is small. (auth)