In future warhead treaty verifications, it could be effective to provide confidence that dismantled non-nuclear items were, in fact, part of a declared nuclear weapon system. We present a novel approach for verifying dispositioned non-nuclear components that leverages existing dismantlement processes in host facilities. This method provides an alternative to intrusive inspection processes of the nuclear weapons production environment, which would require significant changes in the host’s operational behaviors. It achieves this by identifying intrinsic neutron-induced signatures of non-nuclear components to determine their authenticity and estimate the duration they could have existed as part of a nuclear weapons system. The neutron-induced nuclear transmutation on supposed dispositioned parts could reveal the timespans spent in proximity and cooling away from nuclear sources. The presence of long-lived activation products is indicative of long-term inclusion in an assembled device, while short-lived spectator products can provide evidence that the parts were recently removed as a component of a warhead. Further, several common materials in these systems, such as stainless steel, have multiple activation products with differing decay constants. By measuring the ratios of decay gamma-ray emission rates from these materials, the duration of neutron exposure, and thus the lifetime within the warhead, can be confirmed. We will present the results of predictive modeling of measurable signatures from neutron activation for several common non-nuclear materials found in nuclear weapons systems. We observe growing line strengths over a period of years of neutron irradiation, demonstrating that it necessitates decades of exposure to converge to full strength, and thus validating spectroscopy as a probe to irradiation duration. As an analog to warhead verification scenarios, we then model the neutron exposure of non-nuclear components. To validate these models, the gamma-ray signatures of three different stainless steel samples were irradiated with a Californium-252 source over the course of six months at the Sandia National Laboratories. Spectral measurements were collected over a 24-hour period with a highpurity Germanium (HPGe) detector approximately every four weeks. We benchmark these results with simulations and demonstrate that the relative strengths of these lines reflect the time spent in proximity to the neutron source. Lastly, we will present HPGe measurements of signatures obtained from authentic, non-nuclear parts from a dismantled warhead. As the United States has an existing nuclear dismantlement process, which results in limited access to nuclear components but disposition of non-nuclear material, taking advantage of these readily available non-nuclear remnants could provide a welcome and relatively convenient verification process.
Year
2024
Abstract