Experimental Progress Towards a Physical Cryptographic Warhead Verification Protocol

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. Despite several decades of research, no technology has been able to meet these requirements simultaneously. In the past few years, work at MIT has produced a novel physical cryptographic verification protocol that attempts to solve this treaty verification problem. The physical cryptographic protocol 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. Recent progress on the physical cryptographic verification protocol has focused on validating the computational model with experimental data and developing an experimental proof-of-concept. A high-accuracy semi-analytic model of NRF transitions near 2 MeV in Al-27 and U-238 provides improved validation of the NRF computational model, the Geant4 G4NRF Monte Carlo code. Experimental measurements of direct NRF absolute count rates from these Al-27 and U-238 states taken at the MIT High Voltage Research Laboratory in summer 2016 also show agreement with the model within systematic error. Results from early transmission NRF (tNRF) measurements that more closely emulate the verification protocol are also presented.