Gamma Rossi-alpha, Feynman-alpha and Gamma Differential Die-Away concepts as a potential alternative/complement to the traditional thermal neutron based analysis in Safeguards

A new concept for thermal neutron based correlation and multiplicity measurements is proposed in this paper. The main idea of the concept consists of using 2.223 MeV gammas (or 1.201 MeV, DE) originating in the 1H(n,gamma)2D-reaction instead of using traditional thermal neutron counting. Results of investigations presented in this paper indicate that gammas from thermal neutron capture reaction preserve the information about the correlation characteristics of thermal (fast) neutrons in the same time scale. Therefore, instead of thermal neutron detectors (or as a complement) one may use traditional and inexpensive gamma detectors, such NaI, BGO, CdZnTe or any other gamma detectors. In this work we used D8x8 cm2 NaI scintillator to test the concept. Thus, the new approach helps to address the problem of replacement of 3He-counters and problems related to the specific measurements of spent nuclear fuel directly in the spent fuel pool. It has a particular importance for nuclear safeguards and security. Overall, this work represents the proof of concept study and reports on the experimental and numerical evidence that thermal neutron capture gammas may be used in the context of correlation and multiplicity measurements. Investigations were performed for a 252Cf-correlated neutron source and an 241Am-Be-random neutron source. The related idea of Gamma Differential Die-Away approach is investigated numerically in this paper as well, and will be tested experimentally in a future work.