Proposal of direct alpha estimation technique by using ring ratio in the Continuous Neutron Monitor (CNM)

Mukai, Yasunobu ; Nakamura, Hironobu ; Fujisaku, Sakae; Kurita, Tsutomu ; LaFleur, A. M.*; Menlove, H. O.*; Marlow, J. B.*

In case of the Pu mass determination in scattered powder in a GB using Continuous Neutron Monitor (CNM) with totals, self-multiplication of neutron (M) and value are properly required to be set. M can be easily estimated by a simulation code, but it is very difficult to estimate value by such a simulation because interactions between ray generated from Pu and impurities are not consistent. Therefore, we tried to examine an estimation technique of 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 He-3 tubes, we could confirm a good correlation between ring ratio (inner / outer ring count rates) and the values. Thus, we can estimate 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 Pu mass continuously.