R-Value Measurements Performed on Actinide Targets Irradiated using the GODIVA IV Critical Assembly in FY22

The separation and characterization of two irradiated uranium targets, a depleted uranium (DU) and a highly enriched uranium (HEU) target as well as a plutonium (Pu) target, was conducted in April of 2022. The three targets were assembled at Los Alamos National Laboratory (LANL) and irradiated using the GODIVA critical assembly at the National Criticality Experiments Research Center (NCERC). Splits of the dissolved targets were received by Pacific Northwest National Laboratory (PNNL) after which the PNNL and LANL teams chemically separated the solutions using independent separation schemes and analyzed the separated fractions for short lived actinides and fission products. Chemical separations were traced with stable or radioactive tracers to allow for the determination of chemical yields, analyzing using either inductively coupled plasma optical emission spectroscopy (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS) or gamma emission analysis (GEA) depending on the nature of the tracer. The Pu target solution was traced with stable elements at LANL to follow elemental fractionation during a Pu removal step. Many analytical techniques were used by PNNL including kinetic phosphorescence analysis (KPA), ICP-OES, ICP-MS, GEA, and thermal ionization mass spectrometry (TIMS) depending on the analyte’s need. Comparisons were made between PNNL, LANL and literature values for the R-values, number of fissions, activation products, as well as the atoms detected. There was good agreement between the two laboratories for the bulk of analytes. This experiment represents one of the first modern examinations of fission yields for Pu fission induced by fission neutrons. Included in these comparisons were the short-lived actinides 237U, 239Np, the fission products 89Sr, 91Y, 95/97Zr, 99Mo, 111Ag, 115/115mCd, 136/137Cs, 140Ba, 141/143/144Ce, 147Nd, 153Sm, 156Eu, and 161Tb, providing both total atoms as well as the R-values . The data presented in this report represents the first irradiation using the GODIVA critical assembly for this work. .