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

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

To improve safeguards and material accountancy of holdup measurements, a continuous neutron monitor (CNM) that continuously monitors the singles rate from holdup in glove boxes was designed and implemented at PCDF. In totals neutron counting, it is impossible to get Pu mass directly from the singles count rate without predetermination of alpha value and multiplication (M). In case of holdup deposits, since M can be seen as 1, the determination of the alpha value by direct measurement of the holdup is very important. In this research, we have developed a new approach called Direct Alpha Estimation technique. To establish the relation, the ring ratio of the FCAS which has dual ring He-3 tubes was applied. By using different alpha of samples, relation between alpha and ring ratio was studied. As a result, a good correlation between them was obtained. Thus, since the ring ratio can estimate alpha value, we would propose that this technique with dual ringed CNM be extended to not only Pu mass determination, but also to monitor the impurity contents or Pu isotopic composition change in holdup.