Inter-laboratory Redetermination of the Atmospheric 22Ne/20ne

Accurate knowledge of the Ne isotopic composition of air is essential for planetary science. While the uncertainty of the noble gas isotopic composition of air has been drastically reduced to the level of similar to 0.1% in the last few years thanks to modern techniques, the most widely accepted value of the Ne-22/Ne-20 ratio of air (0.102 +/- 0.0008, Eberhardt et al., 1965) has an uncertainty of +/- 0.78% (1 sigma). Here we present the first multi-laboratory re-determination of the atmospheric Ne-22/Ne-20. An artificial, high purity mixture of Ne-20 and Ne-22 was prepared and the Ne-22/Ne-20 (0.11888 +/- 0.00001, 1 sigma) and Ne-20/Ne-22 (8.4118 +/- 0.0007, 1 sigma) determined gravimetrically. This gas was used to determine the mass fractionation of five mass spectrometers allowing the air Ne-22/Ne-20 to be determined (n = 234 analyses). Each laboratory sampled their own local air, used a different gas preparation system and analysis procedure as well as doing their own expansion of the high-pressure artificial Ne gas. Individual air Ne-22/Ne-20 determinations have uncertainties in the range of 0.01-0.08%. The overall reproducibility of the calculated Ne-22/Ne-20 of air between the laboratories shows no overdispersion with respect to the individual uncertainties. We report a global value for the atmospheric Ne-22/Ne-20 of 0.10196 +/- 0.00007 (0.07%, 1 sigma), equivalent of Ne-20/Ne-22 of 9.808 +/- 0.007. This is almost identical to the Eberhardt et al. (1965) value although its uncertainty shows a 12 times reduction. Our study did not verify any of the other previous determinations of atmospheric Ne-22/Ne-20. This highly accurate and precise atmospheric Ne-22/Ne-20 value provides a new reference for atmospheric Ne-21/Ne-20 determinations and we recalculate (Ne-21/Ne-20)(air) of five recent determinations. While this exercise resulted in no significant change to the absolute values, it gives more confidence with respect to the correctness of (Ne-21/Ne-20)(air). We suggest that the revised value for atmospheric Ne-22/Ne-20 be used routinely in all geoscience applications.