CHARACTERIZATION OF THE URANIUM ISOTOPIC ABUNDANCES IN NBL CERTIFIED REFERENCE MATERIAL 125-A

The New Brunswick Laboratory (NBL) of the U.S. Department of Energy (DOE) has been tasked to develop certified reference materials (CRMs) to support nuclear forensic analytical work. As part of this effort, NBL is characterizing several materials for U-Th purification ages and parent-daughter isotopic composition. These materials include CRM 125-A, Uranium Oxide (UO2) Pellet Assay and Isotopic Standard (4% enriched in 235 U). The uranium isotope-amount ratios and amount content of CRM 125-A materials have previously been certified but the 236 U abundance was poorly constrained due to instrumental limitations at the time of original certification. Six randomly selected pellets are analyzed by TIMS to improve the pre-existing certificate values of the uranium isotope-amount ratios in CRM 125-A. The Modified Total Evaporation (MTE) method was used for simultaneous determination of the major and minor isotopic abundances. Additionally, minor n( 234 U)/n( 238 U) and n( 236 U)/n( 238 U) uranium-amount ratios from MTE experiments were verified using a conventional analysis technique that also included corrections for peak tailing effects based on measurement of the backgrounds on the high and low mass side of 234 U and 236 U. The n( 235 U)/n( 238 U) isotopic abundances were also measured using the Total Evaporation (TE) analytical technique. The absence of 233 U in CRM 125-A material was verified by scanning the mass region using a Secondary Electron Multiplier (SEM) equipped with a Retarding Potential Quadrupole (RPQ). The results of the characterization analyses for CRM 125-A are presented here.