Development of synchronous gated readout for neutron-resonance transmission analysis*

Recent work has gone into the development of systems using the resonant absorption of epithermal neutrons to authenticate nuclear warheads slated for dismantlement. The verification exercise involves the host placing a treaty accountable item (TAI), such as the pit of a nuclear weapon, in a visually opaque box, after which the inspectors use neutron-resonance transmission analysis (NRTA) to obtain an isotopic “signature” of the TAI and compare it with that of a previously authenticated “golden copy”. To restrict the information gained, the output of the neutron detector should be gated, to only allow information about the previously agreed upon resonance absorption lines in the ~eV epithermal region from ²³⁹Pu. We have designed an instrument which does this gating, synchronized to a pulsed DT neutron source, effectively suppressing the output of the epithermal neutron detector outside of a set energy window. By constructing this instrument entirely out of discreet analog components, the operation of the circuit is easily verifiable, and randomly selected components can be provided by hosts to further increase trust in the process. The concept will be discussed, and data from experimental NRTA measurements will be presented.