US-DOE and CIAE international cooperation in age-dating uranium standards

In 2014 the United States Department of Energy and the China Institute of Atomic Energy collaborated in a study measuring the model ages of uranium certified reference materials. Lawrence Livermore National Laboratory (LLNL) and Los Alamos National Laboratory (LANL), and the Chinese Institute of Atomic Energy (CIAE) determined 230 Th– 234 U model ages for uranium certified reference materials U010 and U850. The aim of this work was to collaborate with CIAE and compare methods for measuring the age of bulk uranium materials using the 230 Th– 234 U radiochronometer. Accurate results for age-dating depend on the accurate calibration of the tracer materials (e.g., 229 Th and 233 U) used for the isotope dilution mass spectrometry (IDMS) analyses. To facilitate inter-comparison of results, samples of a 230 Th standard reference material were distributed to each laboratory for 229 Th tracer inter-calibration. The resulting 230 Th– 234 U model ages from this collaboration for U010 ranged from March 1956 to January 1959, which agree with the known material production date of June 5th, 1958. The determined model ages for U850 were from December 1955 to October 1957, which agree with the material production date of December 31, 1957. All three laboratories used independent methods to determine model ages for uranium standards that agree with known production ages and with previously reported results.