Standardization of Nuclear Mass Spectrometry Methods for Nuclear Safeguards

A standardized new version of the \"modified total evaporation\" (MTE) method for isotopic analysis of uranium samples by multi-collector thermal ionization mass spectrometry (TIMS) with high analytical performance is described. The development of the MTE method was organized as a collaboration of several nuclear mass spectrometry laboratories, namely the New Brunswick Laboratory (NBL, U.S.DOE), the Safeguards Analytical Laboratory (SAL, now SGAS-Safeguards Analytical Services) of the International Atomic Energy Agency (IAEA), the Institute for Transuranium Elements (JRC-ITU), and the Institute for Reference Materials and Measurements (JRC-IRMM). Due to the use of the “total evaporation” (TE) principle measurements of the \"major\" 235 238 U/ U is routinely being performed with an accuracy of 0.02%. But the most ratio significant improvement using the MTE method is in the measurement performance 238 U/ measurement performance which, depending on the ratio, is several orders of magnitude 234 238 236 U/ U and U. The MTE method provides a superior compared to the IAEA requirement and to the TE method. For routine MTE achieved for the \"minor\" ratios -9 SEM detector combined with an energy filter for detecting the isotope U. The MTE method has proven to be a significant improvement for measuring in 238 U/ reference measurements for development and production of certified reference materials at NBL and JRC-IRMM as well as for nuclear safeguards measurements at the IAEA and JRC-ITU. The collaboration between JRC-IRMM and ASTM-International started with the invitation to develop an ASTM standard document for the MTE method in 2013. The recently released new MTE standard ASTM C1832-16 document does not only provide a detailed description and instructions for users, it also provides information about the typical analytical performance to be expected. This is beneficial to the user in conformity assessment with the deployed quality system, as well as to organizers of interlaboratory comparisons (ILCs), such as JRC-IRMM, NBL, IAEA or others.