A PRIMARY XENON ISOTOPIC GAS STANDARD WITH SI TRACEABLE VALUES FOR ISOTOPIC COMPOSITION AND MOLAR-MASS

A metrological certification measurement was made on a large batch of xenon separated from the terrestrial atmosphere by Messer Griesheim (D uisburg, Germany). The measurements were performed using the same proc edure for measurements of amount ratios as developed for the improveme nt of the Avogadro constant N-A. During the measurement, the gas effus ion from the expansion vessel into the ion source was continuously mon itored by measuring experimental values for [m(E-i)/m(E-j)](-(empty se t)) to enable correction for mass discrimination. Synthetic mixtures w ere made of enriched Xenon isotopes and measured. They did not reveal a significant correction factor for residual unknown errors within the measurement uncertainty of 5 x 10(-4). Thus, an isotopic composition and a molar mass (atomic weight) value M(Xe) = 131.29276 +/- 0.00033 g mol(-1) for xenon in this batch was established by procedures confirm ed by kinetic gas theory at this level. The measured isotope amount ra tios were compared to previous measurements on atmospheric xenon. They are in good agreement but now have considerably smaller relative comb ined uncertainties: n(Xe-124)/n(Xe-132) = 0.003536(12); n(Xe-126)/n(Xe -132) = 0.0033077(72); n(Xe-128)/n(Xe-132) = 0.070989(29); n(Xe-129)/n (Xe-132) = 0.98112(41); n(Xe-130)/n(Xe-132) = 0.151290(47); n(Xe-131)/ n(Xe-132) = 0.789055(76); n(Xe-134)/n(Xe-132) = 0.387819(69); n(Xe-136 )/n(Xe-132) = 0.32916(17). Published by Elsevier Science B.V.