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Emerging thorium-based reactor designs and fuel cycles present challenges to traditional non-destructive assay techniques used in international safeguards. Specifically, assaying the masses of 233U and 235U when they are present together in samples with high gamma ray backgrounds is difficult because of similar passive neutron signatures and relatively weak gamma-ray emissions of 233U. The Pacific Northwest National Laboratory (PNNL) and the Massachusetts Institute of Technology (MIT) are developing a portable neutron resonance transmission analysis (pNRTA) system as one potential solution to these challenges. This method provides isotopic concentration data for a sample via neutron time-of-flight (TOF) measurements that exploit epithermal neutron resonance cross-sections. A recently developed pNRTA system uses a commercially available, pulsed deuterium-tritium neutron generator with a ∼2 m flight path and a GS20 lithium glass scintillator detector. This paper describes the prototype pNRTA system design, a refined radiation transport model of the system, preliminary measurements with thorium and uranium sources, and demonstration of a quantitative isotopic estimation algorithm. [ABSTRACT FROM AUTHOR]

Nuclear disarmament treaties are not sufficient in and of themselves to neutralize the existential threat of nuclear weapons. Technologies are necessary for verifying the authenticity of the nuclear warheads undergoing dismantlement before counting them toward a treaty partner's obligation. Here we present a review of concepts involving isotope-specific resonance processes, Nuclear Resonance Fluorescence (NRF) [1] and Neutron Resonance Transmission Analysis (NRTA) [2, 3], used to authenticate a warhead's fissile components by comparing them to a previously authenticated template. All information is encrypted in the physical domain by the addition of an encrypting filter to the target, leading to measurements with an outcome similar to an equation with two unknowns. Using Monte Carlo simulations and experiments, we show that the measurements readily detect hoaxing attempts, while no significant isotopic or geometric information about the weapon is released. These nuclear techniques can be used to dramatically increase the reach and trustworthiness of future nuclear disarmament treaties. [ABSTRACT FROM AUTHOR]

Neutron Resonance Transmission Analysis (NRTA) uses resonant absorption of neutrons to infer the absolute isotopic composition of a target object, enabling applications in a broad range of fields such as archeology, enrichment analysis of nuclear fuel, and arms control treaty verification. In the past, NRTA involved large user facilities and complex detector systems. However, recent advances in the intensity of compact neutron sources have made compact neutron imaging designs increasingly feasible. This work describes the Monte Carlo (MC) based design of a compact epithermal NRTA radiographic instrument, which uses a moderated, compact deuterium-tritium neutron source and an epithermal neutron detector. Such an instrument would have a wide range of applications and would be especially impactful for scenarios such as nuclear inspection and arms control verification exercises, where system complexity and mobility may be of critical importance. The MC simulations presented in this work demonstrate accurate time-of-flight reconstructions for transmitted neutron energies, capable of differentiating isotopic compositions of nuclear material with high levels of accuracy. A new generation of miniaturized and increasingly more intense neutron sources will allow this technique to achieve measurements with greater precision and speed, with significant impact on a variety of engineering and societal problems. [ABSTRACT FROM AUTHOR]