The pulsed neutron method applied to the interaction between moderators

Abstract

The possibility of using the pulsed neutron method to study two interacting moderators has been investigated. The decay constants have been measured in a system consisting of two polyethylene discs separated along the symmetry axis. The experiments cover a range in decay constants from 10,000 to 40,000 s −1. It is found that m all the experiments, with the exception of those in the limits zero and infinite separation distance, the decay constants are drifting in time. Therefore they cannot, within the scope of the experiments in this article, be looked upon as discrete modes or reliable pseudomodes. This behaviour has been confirmed by a qualitative theoretical investigation. The result can be extended to include all experiments with the pulsed neutron method applied to moderators containing cavities or having concave boundaries. A method to eliminate the drifting effect through the incorporation of absorbers in the cavities is suggested.