Construction of a newly designed small-size mass spectrometer for helium isotope analysis; Toward the continuous monitoring of He/He ratios in natural fluids

He/He比の連続測定に向けた小型ヘリウム質量分析計の新規開発

馬上 謙一*; 角野 浩史*; 豊田 岐聡*; 岡崎 隆司*; 大澤 崇人 ; 石原 盛男*; 交久瀬 五雄*; 野津 憲治*; 五十嵐 丈二*; 長尾 敬介*

Bajo, Kenichi*; Sumino, Hirochika*; Toyoda, Michisato*; Okazaki, Ryuji*; Osawa, Takahito; Ishihara, Morio*; Katakuse, Itsuo*; Notsu, Kenji*; Igarashi, Joji*; Nagao, Keisuke*

新規にヘリウム同位体比の測定のためのセクター型質量分析計を開発した。これはさまざまな地球化学試料、たとえば地下水や温泉ガス等に応用できる。質量分解能は約490で、これはHeとHDなどを十分に分解できる性能である。Heで3000000原子を検出できる高い感度を持つ。長期安定性テストでも約3%の再現性と5%以下の不確かさを示した。同位体比の確度においては既存の質量分析計と良い一致を示した。

The construction of a small-size, magnetic sector, single focusing mass spectrometer (He-MS) for the continuous, on-site monitoring of the He isotope ratio (He/He) is described. The instrument is capable of measuring He/Ne ratios dissolved in several different types of natural fluids of geochemical interest, such as groundwater and gas from hot springs, volcanoes and gas well fields. Ion optics of the He-MS was designed by using the ion trajectory simulation program TRIO so as to measure He and He simultaneously with a double collector system under mass resolution power of 500. Presently attained specifications of the He-MS are; (1) mass resolving power of ca. 490, enough to separate He from interfering ions, HD and H, (2) ultra-high vacuum condition, and (3) high sensitivity enough to detect He amount 3000000 atoms).