A multi-energy model for fissile mass estimation

This paper presents a multi-energy model for estimation of fissile mass. The model assumes that each neutron in the system has a different detection efficiency and die-away time, depend- ing on the neutron initial energy. By using the stochastic transport equation, two fissile mass estimation methods are derived under the multi-energy model: time interval analysis using the Rossi-alpha distributions, and fixed-interval detection analysis using the SVM formalism. The methods were 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 Institue of Isotopes in Hungary. The presented model accurately describes results, seen over the years, of neutron detection systems with more than a single exponential die-away time, and has the potential to reduce systematic errors.