On the use of [formula omitted]/n correlations in multiplicity counting in small samples

Abstract

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.We conclude that γ/n coincidence counting still has potential capabilities when the objective is the detection of plutonium, but its use for plutonium effective mass quantification is limited compared to n/n coincidence counting. Nevertheless, the method could still be applicable for the purpose of plutonium mass quantification by using a calibration curve that is specific to a sample’s mass and size.