Evaluation of Plutonium Oxidation Using Pulsed Neutron Measurements with 252Cf

The unrecognized oxidation of plutonium in “sealed” canisters poses a unique problem for both material control and accountability. A feasibility study was performed to address the use of randomly pulsed neutron measurements with 252Cf to determine if plutonium metal in a canister has oxidized without opening the container. The Monte Carlo code MCNP-DSP was used to determine if time-of-flight transmission measurements could be used to determine oxidation of plutonium in “sealed” cans. In the Monte Carlo models, a plutonium button in a can was positioned between a 252Cf source and a scintillation detector, and the time distribution of counts after 252Cf fission in the detector was calculated. The time distribution of counts after 252Cf fission differs between plutonium metal and plutonium oxide because resonances in oxygen will affect transmission of certain energy neutrons from 252Cf. The measurements are practical and could be performed with small 252Cf sources in ionization chambers. This method could be used to determine the presence of other materials that react with plutonium in “sealed” cans.