Uranium Isotopic Measurements Using a New Uranium Hexafluoride (UF6) Gas Source Mass Spectrometer for Certification of Reference Materials and Nuclear Safeguards Measurements at IRMM

The European Commission's Institute for Reference Materials and Measurements (IRMM) is provides isotope reference materials and reference measurements not only to the EU member states but also to the entire international safeguards community. This does not only include various types of specific and tailor-made reference materials but also the development of new reference measurement methods and their implementation. In late 2010 a new gas source mass spectrometer (GSMS) for uranium isotopic measurements using uranium hexafluoride (UF6) gas, the \"URANUS\", was installed at IRMM. By that IRMM is expanding the applicability of UF6 measurements by including the so-called \"minor\" isotope ratios n(234U)/n(238U) and n(236U)/n(238U). In this paper the design and the implementation of measurement techniques for the new \"URANUS\" UF6-GSMS are described. This includes both the single and the double standard method. In addition, the measurement performance for the \"minor\" isotope ratios n(234U)/n(238U) and n(236U)/n(238U) and the first results for test measurements using certified reference materials will be presented. In conclusion, IRMM who is acting as the reference laboratory for nuclear isotopic measurements within the European Union has thereby established two complementary techniques for measuring the full isotopic composition of uranium samples. UF6-GSMS is considered the preferred technique for the major ratio n(235U)/n(238U) while thermal ionization mass spectrometry (TIMS), in combination with the \"modified total evaporation\" (MTE) method, provides the best measurement performance for the \"minor\" isotope ratios n(234U)/n(238U) and n(236U)/n(238U).