On the Uniqueness of Nuclear Warhead Signatures

Whenever the authentication of nuclear weapons or fissile material relies on radioactive emissions (“signatures”), it is important that these signatures are unique. The signature’s uniqueness depends both on the authenticated object itself as well as the measurement approach. Malicious actors can potentially exploit non-unique signatures by imitating them with hoax objects, and therefore cheat disarmament verification processes. The question of the uniqueness of passive emissions was raised several decades ago. In recent years, multiple researchers addressed this question, looking at measurement approaches for photons and neutrons. This article discusses the approaches used in recent analyses of uniqueness. It presents different notional nuclear weapon models, and their respective passive emissions. For photons, the main question is whether the energy distribution of emitted photons is unique. For neutrons, it is whether the time distribution of neutrons could be replicated by hoax objects, thus fooling neutron multiplicity measurements. The article will conclude by outlining future research needs regarding passive signature uniqueness.