Accurate Determination of the Absolute 3He/4He Ratio of a Synthesized Helium Standard Gas (Helium Standard of Japan, HESJ): Toward Revision of the Atmospheric 3He/4He Ratio
Accurate Determination of the Absolute 3He/4He Ratio of a Synthesized Helium Standard Gas (Helium Standard of Japan, HESJ): Toward Revision of the Atmospheric 3He/4He Ratio
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DOI：
10.1029/2018gc007554
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发表时间：
2018-10-01
影响因子：
3.5
通讯作者：
Oide, Hideyuki
中科院分区：
文献类型：
--
作者：
Mishima, Kenji;Sumino, Hirochika;Oide, Hideyuki
日本的氦标准，简称为HESJ，是实验室间的He-3/He-4比值标准。虽然HESJ的He-3和He-4的比率先前通过与大气氦的相对比较来确定，但HESJ的He-3/He-4比率的绝对值尚未直接确定。因此，它依赖于对大气氦的早期测量。大气绝对He-3/He-4比率和包括HESJ在内的其他工作标准的准确性对于氦同位素的某些应用至关重要，例如氚He-3测年、基于宇宙成因He-3的表面暴露年龄确定以及准确测量中子寿命。在这项工作中，新的控制样品的氦气与He-3/He-4的比例为14，28和42 ppm的制造精度为0.25-0.38%，使用气体处理系统的中子寿命实验在日本质子加速器研究综合体。这些样品和HESJ的相对He-3/He-4比率使用磁扇区型，单聚焦，惰性气体质谱仪与双收集器系统测量。结果表明，HESJ中He-3/He-4的绝对比值为27.36 ± 0.11ppm。在此基础上，测得大气中He-3/He-4比值为1.3400.006ppm。氦有两种同位素，He-3和He-4。这两种同位素有不同的起源。地球中的He-3是最初在地球形成过程中被捕获的物质的残余，而主要由铀和钍的放射性衰变产生的He-4已被添加到原始He-4中，这意味着氦的两种同位素的比例可以用作地球化学和宇宙化学中的强大示踪剂。本文利用粒子物理实验装置，准确地测量了标准校准器的He-3/He-4比值，其测量精度为0.4%。用此结果测定了大气氦的He-3/He-4比值，其精度比以往任何时候都高。
The helium standard of Japan, referred to as HESJ, is an interlaboratory standard for the He-3/He-4 ratio. While the ratio of He-3 and He-4 of the HESJ was previously determined by a relative comparison to atmospheric helium, the absolute value of the He-3/He-4 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 He-3/He-4 ratios of the atmosphere and other working standards including HESJ is crucial in some applications of helium isotopes, such as tritium-He-3 dating, surface-exposure age determination based on cosmogenic He-3, and the accurate measurement of the neutron lifetime. In this work, new control samples of helium gases with He-3/He-4 ratios of 14, 28, and 42ppm 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 He-3/He-4 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 He-3/He-4 ratio of the HESJ was determined as 27.360.11ppm. The atmospheric He-3/He-4 ratio was determined as 1.3400.006ppm, based on this work.Helium has two isotopes, He-3 and He-4. The two isotopes have different origins. He-3 in the Earth is a vestige of that which was originally trapped during the Earth's formation, whereas He-4 generated mainly by radioactive decays of uranium and thorium has been added to primordial He-4, which means that the ratio of the two isotopes of helium can be used as a powerful tracer in geochemistry and cosmochemistry. In this work, we accurately measured the He-3/He-4 ratio of a standard calibrator by using an apparatus for a particle physics experiment and determined its value with an accuracy of 0.4%. By using the present result, the He-3/He-4 ratio of atmospheric helium was determined with best the accuracy ever than that before.