A method for the estimation of fissile mass by measuring the number of neutron signals within a specific time interval

This paper presents a new method for fissile mass estimation by passive neutron interrogation. The method uses the stochastic transport equation to express the first three central moments (mean, variance and skewness) for the number of detected neutrons within a given time interval in terms of the fissile mass, the (α,n) rate and the multiplicity factor. Solving these three equations allows estimation of the fissile mass. As the primary validation of the method, it was implemented for several fissile mass measurements, which were conducted by the Nuclear Security Unit of the Joint Research Center (JRC) in Italy and by the Institute of Isotopes in Hungary.