Upgrading ENDF: Reaction Models and Formatting for Gamma Ray Production

Neutron induced reactions generate gamma-rays that are unique to the target isotope, and the resulting spectra can be used as a fingerprint to identify the irradiated object. The so-called active neutron interrogation relies on evaluated nuclear data together with transport simulations and is employed in oil well logging, safeguards, planetary space science, etc. The available nuclear data libraries and modelling tools are incomplete, and there is strong need to improve the necessary tools to support interrogation applications. The deficiencies impact both secondary gamma emission, and correlations between deexcitations and neutron emissions. We are revising the gamma production data and formats in ENDF/B-VIII.0 to extend the modelling of particle-gamma and gamma-gamma coincidences. Our goal is to provide an in-line gamma cascade capabilities for both primary gammas and secondary cascade emissions, in addition to updating branching rations, energy levels, and gamma-ray energies. Here, we present selected results for gamma emissions from the neutron absorption channel. We model primary and cascade gammas with different reaction codes and compare the obtained spectrum to tabulated data from CapGam. Our efforts will support transport codes, e.g. MCNP, GEANT4, and Mercury.