Performance Characterization of a Water-based Multiplicity Counter

Year
2014
Author(s)
N. S. Bowden - Lawrence Livermore National Laboratory
A. Bernstein - Lawrence Livermore National Laboratory
S. Dazeley - Lawrence Livermore National Laboratory
V. Mozin - Lawrence Livermore National Laboratory
A. Asghari - Department of Nuclear Engineering, University of California, Berkeley
Abstract
In recent years the severe shortage of 3 He has necessitated the fast development of new neutron detection technologies. Here we report the performance characteristics of a water-based neutron detecting multiplicity counter for the non-destructive assay of fissile sources. We measured an absolute neutron detection efficiency of 28% and 60Co rejection/suppression factor of ~108 to 1. For sources with higher background gamma ray intensities, the neutron efficiency was 22% ± 1% up to a 60Co equivalent rate of 4 MBq. We also present the sensitivity to small spontaneous fission sources such as 252Cf and 240Pu. By simulating a selection of isotopes and activities, we determine whether they can be distinguished by the neutron multiplicity distribution. If source related gamma ray rates are low, we have found that the multiplicity distributions of 240Pu, 252Cf and background should be distinguishable for source fission rates as low as ~10 Hz, corresponding to approximately 24 milligrams of 240Pu.