JAEA/ISCN Delayed Gamma-ray Spectroscopy Inverse Monte Carlo
Development Status

The Integrated Support Center for Nuclear Nonproliferation and Nuclear Security (ISCN) of the Japan Atomic Energy Agency (JAEA) is developing Delayed Gamma-ray Spectroscopy (DGS) for safeguards capabilities. DGS is a non-destructive assay technique that utilizes neutrons to induce fission in the sample followed by a measurement of gamma rays emitted by the short-lived fission products as they decay. The primary DGS outcome is to evaluate the composition using the ratio of these gamma-ray peaks and the relative fissilenuclide contribution. Significant progress has been made toward analyzing the gamma-ray peaks in order to evaluate the composition, as well as the mass, of fissile nuclides found in mixed nuclear material, like irradiated fuel. Specifically, the JAEA/ISCN is developing and inverse Monte Carlo (IMC) analysis method wherein the composite spectrum from a laboratory interrogation is compared to expected spectra from Monte Carlo (MC) simulations. Preliminary MC spectra show reasonable comparisons to measured spectra, though sufficient differences required further experimental confirmation. This work describes the recent efforts made to validate the JAEA/ISCN DGS MC through extended comparisons to measured spectra and other MC simulation programs. Further, we show how our MC comparison method has potential to assist in improving nuclear data useful for evaluating fission yields for nuclear safeguards and nuclear energy material accountancy.