Proposal of direct alpha estimation technique by using ring ratio in the continuous neutron monitor (CNM)

In case of the Pu mass determination in scattered powder in a glovebox using Continuous Neutron Monitor (CNM) with totals, self-multiplication of neutron (M) and alpha value are properly required to be set. M of scattered powder can be easily estimated by a simulation code, but it is very difficult to estimate alpha value by such a simulation because interactions between alpha ray generated from plutonium and impurities in the powder are not consistent. Therefore, we tried to examine an estimation technique of alpha value by direct measurement. As a result, by measuring the samples taken from the scattered powder using a multiplicity counter with a dual ring structure of ³He tubes, we could confirm a good correlation between ring ratio (inner ring count rates / outer ring count rates) and the alpha values. Thus, we can estimate alpha value in the powder directly by the ring ratio measurement. By applying this technique to CNM and designing a new detector with a double layer structure of neutron detection tubes, we had a prospect that CNM would be able to measure the plutonium mass continuously. (author)