Measurement and Simulation of Neutron/Gamma-Ray Cross-Correlation Functions from Spontaneous Fission

We present an application of a digital pulse shape discrimination (PSD) technique for the novel measurement of cross-correlation functions from a spontaneous fission source. The measurement method allows for the collection of fast coincidences within a time window of the order of a few tens of nanoseconds. The use of PSD allows for the accurate acquisition of the coincidences in all particle combinations. Specifically, separate neutron–neutron, neutron–gamma-ray, gamma-ray–neutron, and gammaray–gamma-ray coincidences are acquired with two liquid scintillation detectors. The measurements are compared to results obtained with the MCNP-PoliMi code, which simulates neutron and gamma-ray coincidences from a source on an eventby-event basis. This comparison leads to relatively good qualitative agreement. Simulations of the separate neutron and gamma-ray contributions to the total cross-correlation function help to further improve the performance of experimental systems that aim at accurate identification of nuclear materials. This research has direct applications in the areas of nuclear nonproliferation and homeland security.