Delayed Gamma-Ray Spectroscopy Inverse Monte Carlo Analysis Method for Nuclear Safeguards Nondestructive Assay Applications

The Japan Atomic Energy Agency and European Commission Joint Research Centre (JRC) are collaborating to develop technology to improve the ability to quantify the uranium and plutonium content of high radioactivity and mixed nuclear material (e.g. spent nuclear fuel, plutonium-nitrate solution, mixed-oxide) for nuclear safeguards verification. A comprehensive system using a pulsed neutron source will integrate multiple active neutron interrogation techniques: differential die-away analysis, prompt gamma-ray analysis, neutron resonance transmission analysis, and delayed gamma-ray spectroscopy. Due to the current limitations of delayed gamma-ray spectroscopy, a parallel program focuses on improving the capability to measure, analyze, and predict the delayed gamma-ray spectrum used to determine the nuclide ratios within a sample. Measurements performed at the JRCIspra in Italy are used to correlate the observed delayed gamma rays to the composition that are then used to calibrate a delayed gamma-ray Monte Carlo. The Monte Carlo has the ability to predict expected delayed gamma rays, provide a sensitivity analysis to optimize future measurements, and can be used to analyze a spectrum using an inverse Monte Carlo technique. Analyzing Monte Carlo with this inverse Monte Carlo analysis provides a way to determine systematic uncertainty as well as statistical uncertainty when multiple measurements are not feasible. This work will describe the efforts to develop the delayed gamma ray Monte Carlo and how it will be utilized for current and future applications.