DETERMINATION OF THE ISOTOPIC COMPOSITION AND ATOMIC-WEIGHT OF TUNGSTEN USING GAS-SOURCE MASS-SPECTROMETRY - OPENING THE ROUTE TO THE ESTABLISHMENT OF THE TRACEABILITY OF TUNGSTEN AMOUNT MEASUREMENTS TO THE SISYSTEM

The isotopic composition of W in a sample of WF6 was determined using gas source mass spectrometry. The values obtained correspond well with the present internationally accepted IUPAC values, but the uncertaint ies are considerably smaller. The measurement procedures used are iden tical to those used for silicon isotopic measurements on SiF4, as used in the Avopdro projects for which IRMM provides the silicon molar mas s. The values obtained can therefore be considered to be ''near-absolu te''. The potential of this approach for a possible establishment of t raceability to the SI system of W amount measurements (''chemical meas urements'') is discussed.