Analysis of Pulsed Neutron Experiments in Polycrystalline Media Using a Model Kernel

A detailed investigation of pulsed neutron experiments in thermal, nonmultiplying, polycrystalline moderators is presented. A transport approximation of the spatial dependence of the neutron density and a simplified scattering kernel are employed. The dispersion law is examined in some detail both analytically and numerically and comparisons are made with experimental data and multigroup calculations for beryllium and graphite. It is found that even in very small systems, the decay may be well represented by a single exponential. However, if the system is too small, the very long time behavior is controlled by a continuum, non-exponential, contribution.