Monte Carlo simulations of a physical cryptographic warhead verification protocol using nuclear resonance fluorescence

Abstract

Future multilateral nuclear arms reduction efforts will require technologies for the verification of treaty compliance. In particular, warheads slated for dismantlement will need to be verified for authenticity without revealing any sensitive weapons design information to international inspectors. Recent efforts have investigated physical cryptographic verification protocols that attempt to solve this treaty verification problem by using physics processes rather than electronics to encrypt sensitive information. The physical cryptographic protocol simulated in this thesis exploits the isotope-specific nature of nuclear resonance fluorescence (NRF) measurements to provide a strong indicator of the authenticity of a warhead. To protect against sensitive information leakage, the NRF signal from the warhead is convoluted with that of an encrypting foil containing the same isotopes as the warhead but in unknown amounts. The convoluted spectrum from a candidate warhead is then statistically compared against that from an authenticated template warhead to determine whether the candidate itself is authentic. This work presents the initial Geant4 Monte Carlo simulations of the physical cryptographic warhead verification protocol. Using a 2.7 MeV endpoint bremsstrahlung beam, a template warhead is interrogated. Several hoax geometries are also compared against the template to show the protocol's robustness against cheating. Isotopic hoaxes in which weapons-grade plutonium is replaced with reactor-grade plutonium or depleted uranium are shown to be detectable in realistic measurement times. An optimized geometric hoax that mimics the areal densities and attenuations of the authentic template warhead along one axis can also be detected with a second measurement under a different projection. Results of the simulations as well as future research objectives will be presented and discussed.