On the use of γ/n correlations in multiplicity counting in small samples

The use of liquid scintillation detectors provides the possibility to acquire information about both γ-rays and neutrons. The capability of plutonium detection via γ/n coincidences in liquid scintillation detectors is well demonstrated in the literature, and it is also acknowledged that correlated γ/n detection can offer better sensitivity and signal to noise ratio compared to neutron–neutron for some applications. In this paper we perform an assessment of the use of γ/n coincidence counting in small samples, what may have use in the context of nuclear safeguards. We formulate the expected number of γ/n coincidences and calculate the average and covariance of γ-ray and neutron multiplicities for 238Pu, 240Pu, 242Pu and 252Cf. The multiplicative coefficients for the 240Pu effective mass equation was then calculated using γ/n coincidences, and Monte Carlo simulations performed in order to model the detection of neutrons and γ-rays inside liquid scintillation detectors.