THE ROLE OF MASS SPECTROMETRY IN THE CERTIFICATION OF URANIUM REFERENCE MATERIALS

Certification of uranium reference materials for isotopic composition requires mass spectrometry measurements that can achieve the smallest possible combined uncertainties. Current efforts to achieve lower total uncertainties for the next generation of uranium reference standards at New Brunswick Laboratory (NBL), the U.S. federal certifying authority for nuclear materials, are described. In summary, lower uncertainties result from the following notable developments: 1.) the combined use of very high-precision gas (UF6) mass spectrometry and thermal ionization mass spectrometry, 2.) the upgrade of thermal ionization mass spectrometer detectors, 3.) the use of a new multi-stage thermal ionization mass spectrometer capable of very high abundance sensitivity measurements, 4.) production of new primary isotopic calibration mixtures, 5.) use of more precise instrumental calibration procedures, and 6.) use of a new Class 100 cleanroom for sample preparation.