Development of a portable active interrogation system for characterizing special nuclear material

Detection, identification, and characterization of shielded Special Nuclear Material (SNM), and especially of Highly Enriched Uranium (HEU), often require active interrogation. Active interrogation with neutrons or high energy photons induces fission and thus causes the emission of characteristic gamma and neutron radiation. The detection of the emitted radiation with simple detector systems often only indicates the presence of SNM. Analysis of the correlations of the neutron emissions can provide characteristics of a material, such as multiplication and mass. Such analyses are used in well counters for characterizing SNM. Our system consists of a portable pulsed neutron generator and a portable list-mode neutron detection system. The neutron correlations between the intense interrogating pulses from the neutron generator are analyzed to determine characteristics of the SNM. After the last interrogating pulse, the die away is analyzed to identify the type of SNM. We report data from a variety of SNM objects and present preliminary analysis results.