Neutron multiplicity moments with detector cross-talk

Abstract

Passive neutron multiplicity counting (NMC) methods extract the intensity of a primary fission source from the measured moments of the count distribution. This extraction is typically derived using a stochastic point model, assuming neutrons are generated by the primary fission source, a secondary induced one, and an α,n source.Traditional NMC is based on neutron absorption in 3He tubes, embedded in a moderating medium. For such systems, the point models were adapted to the time scales of the moderation and absorption. Recent years have seen a growing interest in the development of NMC based on neutron scattering in scintillators, in part due to the increase in demand for 3He. This poses the need to adapt the models to scattering-based systems.This paper addresses a key feature evident only in scattering-based systems: the so-called detector cross-talk, created by neutron re-scattering in multiple detectors. We derive a novel model for the sampled NMC moments which takes into account the detector cross-talk. The model assumes that the typical time scale of cross-talk is significantly shorter than the average neutron lifetime, which allows considering multiple detections due to detector cross-talk as simultaneous events.