Fissile Mass Estimation by Pulsed Neutron Source

Passive methods for detecting correlative neutrons from spontaneous fissions (e.g. multiplicity and SVM) are widely used for fissile mass estimations. These methods are feasible for materials that emit a significant amount of fission neutrons (like plutonium). Active interrogation, in which fissions are induced on the tested material by an external fixed or pulsed neutron source, has the potential advantages of fast measurement alongside independency of the spontaneous fissions rate of the tested material (enables uranium measurement). Uranium mass estimation by active interrogation with fixed neutron source requires additional information of the coupling between the neutron source and the sample, which depends on the sample's geometry, density and isotopic composition. Pulsed active neutron interrogation techniques, e.g. differential die away analysis (DDA), are very sensitive for the detection of the presence of fissile materials as well as the classification of the type of cargo being inspected, but lack the ability of fissile material mass estimation. Recently, both, the multiplicity and the SVM techniques, were theoretically extended for analyzing active fissile mass measurements, made by a pulsed neutron source. In this study we experimentally examined, for the first time, the SVM technique for pulsed neutron source. The measurements were conducted at the PUNITA facility of the Joint Research Centre. Promising, but still preliminary, results of mass estimation by pulsed neutron source technique are presented.