Comparison of Deadtime Correction Factors for Passive Neutron Multiplicity Counting of Correlated and Non-Correlated Neutron Sources - 9298

Traditional deadtime correction methods for Passive Neutron Multiplicity Counting (PNMC) have been found to be potentially accuracy limiting at high average (or sustained) count rates and in the case where highly correlated rates occur over a short coincidence gate width (high instantaneous rates associated with high multiplicity bursts). It is costly to retrofit new hardware to existing assay systems to reduce the effects of deadtime, thus it is advantageous to develop and implement new deadtime correction algorithms as an alternative approach to ameliorate this problem. Future counter designs trend towards higher efficiencies and shorter dieaway times and hence these designs will also present the need for improved deadtime treatments as they will get applied to more demanding applications. For these reasons, deadtime correction techniques for PNMC are currently being re-visited by both the waste characterisation and safeguards communities in the nuclear industry. A Monte Carlo approach has been established to simulate deadtime behaviour in PNMC systems and applied to this long standing problem. The form of the deadtime correction factor has been investigated for non-correlated (e.g. AmLi) neutron sources and will be extended to correlated (e.g. Cf-252) neutron sources. This paper addresses the practical correction method in each case. The aim of this work has been to aid research into the development of an improved and unified approach to deadtime correction for different multiplicity distributions. Simulation provides a convenient means to examine the range of applicability of current analytical models.