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The helium standard of Japan, referred to as HESJ, is an interlaboratory standard for the  3 He/ 4 He ratio. While the ratio of  3 He and  4 He of the HESJ was previously determined by a relative comparison to atmospheric helium, the absolute value of the  3 He/ 4 He ratio of the HESJ has not been directly determined yet. Therefore, it relies on the early measurements of that of atmospheric helium. The accuracy of the absolute  3 He/ 4 He ratios of the atmosphere and other working standards including HESJ is crucial in some applications of helium isotopes, such as tritium‐ 3 He dating, surface‐exposure age determination based on cosmogenic  3 He, and the accurate measurement of the neutron lifetime. In this work, new control samples of helium gases with  3 He/ 4 He ratios of 14, 28, and 42 ppm were fabricated with accuracy of 0.25–0.38% using a gas‐handling system for a neutron lifetime experiment at Japan Proton Accelerator Research Complex. The relative  3 He/ 4 He ratios of these samples and the HESJ were measured using a magnetic‐sector type, single‐focusing, noble gas mass spectrometer with a double collector system. As a result, the absolute  3 He/ 4 He ratio of the HESJ was determined as 27.36 ± 0.11 ppm. The atmospheric  3 He/ 4 He ratio was determined as 1.340 ± 0.006 ppm, based on this work.

geochemistry, geophysics, geosystems

Accurate Determination of the Absolute  3 He/ 4 He Ratio of a Synthesized Helium Standard Gas (Helium Standard of Japan, HESJ): Toward Revision of the Atmospheric  3 He/ 4 He Ratio