Re-certification of a series of uranium isotope reference materials:: IRMM-183, IRMM-184, IRMM-185, IRMM-186 and IRMM-187

The isotopic composition of the widely used series IRMM 183-187 (IRMM-183, IRMM-184, IRMM-185, IRMM-186 and IRMM-187) of uranium isotope reference materials with 215 U abundances ranging from depleted to low enriched uranium (ca. 0.3%, 0.7%, 2.0%, 3.0% and 4.5%) was first certified in 1987 and updated in 1993 and 1999. Progress in the development of mass spectrometric instrumentation over the past 20 years has led to the precision and reliability of isotope ratio measurements being gradually improved. After a new thermal ionization mass spectrometer (TIMS) was installed at IRMM in January 2004, the isotopic composition of the IRMM 183-187 series was re-measured and re-certified with significantly reduced uncertainties for the U-234/U-238 and U-236/U-238 isotope ratios. The reliability of the new data was confirmed by verification measurements of synthetic isotope mixtures including the IRMM-072 series to demonstrate the linearity of both Faraday and ion counting detectors, as well as by using new synthetic calibration mixtures with U-236/U-238 ratios in the order of 10(-6), 10(-7) and 10(-8) to validate measurements of U-236 in ion counting mode. (c) 2005 Elsevier B.V. All rights reserved.