Low-resolution Gamma-ray Spectrometry for an Information Barrier Based on the Template-Matching Approach

Gamma-ray spectrometry has been successfully employed to identify unique items containing special nuclear materials. The technique is particularly sensitive to the iso- topics near the surface of an inspected item and its projected surface area (or its minimum mass). Here, we present a warhead authentication system based on low-resolution measure- ments, which, by design, reduces the extent of revealed sensitive information. A polyethylene insert can be placed in front of the detector in order to detect important evasion attempts and to assess in particular whether an item’s absolute mass of fissile material correspond to the mass of a reference item. Neutrons from spontaneous or induced fission events in the item produce 2.22 MeV gammas from (n,?) reactions in the insert. This supplementary gamma signature scales with the mass of the item and provides extra sensitivity of the inspection system. While the intensity of spontaneous fission neutrons from plutonium is sufficient to confirm the item’s mass, a californium-252 source can be added to obtain a neutron signature from induced fission in uranium items.