Pulsed moderator studies using a time focused crystal spectrometer

Abstract

A technique is reported for measuring the joint time and energy dependence of the rate of emission of slow neutrons emerging from moderators pulsed with fast neutrons. A crystal spectrometer selects neutrons of a given energy and the leakage flux of that energy is examined as a function of time. The spectrometer is arranged to be time-focussed; time resolution is decoupled from energy, spatial and angular resolution. Time-focusing enables measurements to be made using a 14 MeV neutron source of 1011 n/sec peak intensity.Time widths for several polyethylene moderators are reported. The leakage spectra as a function of energy are also measured using conventional time of flight techniques. The absolute yield per incident neutron is measured.