Propagation of Neutron Waves in Moderating Media

Use of a sinusoidally modulated source of neutrons is equivalent to “poisoning” a moderating medium with a 1/v poison. The inverse relaxation length of the neutron wave amplitude and the variation of the phase angle as a function of position are dependent upon the frequency of modulation and the neutron diffusion and thermalization parameters of the media in which the waves are being propagated. The neutron wave technique allows “poisoning” of solid moderators and provides a means of performing poisoning experiments for measuring nuclear properties of solid as well as liquid moderators. It should supplement the recent use of poisoning techniques in an attempt to reconcile discrepancy in the diffusion and thermalization parameters of moderators, as measured by pulsed neutron techniques. The neutron wave technique and the pulsed neutron technique are supplementary from an experimental viewpoint.