The Time-Dependent Thermal Neutron Flux from a Pulsed Subcritical Assembly

A two-group analysis has been applied to the transient behavior of the thermal flux in a subcritical assembly which has been given a short burst of fast neutrons. This analysis has been applied to graphite-U²³⁵ reactors having moderator-to-fuel (C/U) atomic ratios of 600, 1200, 2340, and 9550. The results are shown to be in agreement with measurements of the decay of thermal neutrons when short pulses of fast neutrons are incident on assemblies having these C/U ratios.