Progress On Plutonium Isotopic CRM 946, 947 And 948 Recertification

Lawrence Livermore National Laboratory (LLNL) and the NBL Program Office (NBL PO) are collaborating on production of purified sub-units of the former NBS 936, 937 and 938 plutonium isotopic reference materials, which will be distributed as certified reference materials (CRMs) CRM 136A, CRM 137A, and CRM 138A, respectively. These reference materials, employed throughout the United States and international community as standards for isotopic measurement method calibration and quality control, are now over 50 years old and currently packaged in 0.25 g units that are inconvenient to ship and much larger than typically needed by analytical laboratories. To reduce their radioactivity and potentially enable their use as Pu radiochronometry reference materials, a two-stage anion exchange purification will be performed to significantly reduce the quantities of U, Am, and Np in the source material. Purification methods were tested on 100 µg sub-units of NBS 947 (CRM 137). The concentrations of Pu, U isotopes, 241Am, and 237Np in the starting material were measured via isotope dilution (ID) multicollector–inductively coupled plasma–mass spectrometry (MC-ICP-MS). Results demonstrate that sub-units were completely purified of 241Am in September 1970, at which time 237Np content was approximately 280 ppm. This is consistent with the known history of NBS 947, however Pu-U chronometers gave model ages in March-April 1972, indicating that U was partially fractionated sometime after purification. Initial concentrations were combined with MC-ICP-MS U, Pu and Am measurements of the purified aliquots and gamma spectrometry with a 239Np tracer to calculate yield and decontamination factors, which were 1.66E+03, 1.14E+05, and 6.29E+02 for U, Am, and Np, respectively. The procedure was scaled up to purify approximately 245 mg of CRM 137 in a new glovebox at LLNL. After gamma spectrometry verified acceptable yield and purification of Am and Np, the purified Pu was dissolved in nitric acid and aliquoted into individual units of approximately 1 mg Pu as dry nitrate in FEP Teflon bottles. The purification and production of CRM 137A units, and plans for analytical measurements leading to assignment of values and certification, will be discussed.Prepared by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-819650