Activities in a program to develop techniques in the use of pulsed neutron sources to measure shutdown parameters related to large thermal power reactors are reported. The experimental work centers around aspects of detecting neutrons in the presence of 10/sup 7/ r/hr gamma fields. The feasibility of U/ sup 235/ coated solid state detectors for use in these measurements is being studied. A theoretlcal investigation is also in progress on the effects of a multi-region assembly on the fundamental decay constant of injected bursts of neutrons. Other work is reported on the time-dependent neutron thermalization for bare multiplying media, particular attention is directed to the exponential time decay for pulsed bare multiplying homogeneous assemblies. Numerical expressions are given for the fundsmental eigenfunction and eigenvalue to the first and second order, respectively. An explicit analytical expression for the eigenfunction is included. (J.R.D.)