title: Construction of a newly designed small-size mass spectrometer for helium isotope analysis: toward the continuous monitoring of (3)he/(4)he ratios in natural fluids.
abstract: The construction of a small-size, magnetic sector, single focusing mass spectrometer (He-MS) for the continuous, on-site monitoring of He isotope ratios ((3)He/(4)He) is described. The instrument is capable of measuring (4)He/(20)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. The ion optics of He-MS was designed using an ion trajectory simulation program "TRIO," which permits the simultaneous measurement of (3)He and (4)He with a double collector system under a mass resolution power (M/ΔM) of >700. The presently attained specifications of He-MS are; (1) a mass resolving power of ca. 430, sufficient to separate (3)He(+) from interfering ions, HD(+) and H3 (+), (2) ultra-high vacuum conditions down to 3×10(-8) Pa, and (3) a sufficiently high sensitivity to permit amounts of (3)He to be detected at levels as small as 10(-13) cm(3) STP (3×10(6) atoms). Long term stability for (3)He/(4)He analysis was examined by measuring the (3)He/(4)He standard gas (HESJ) and atmospheric He, resulting in ∼3% reproducibility and ≤5% experimental error for various amounts of atmospheric He from 0.3 to 2.3×10(-6) cm(3) STP introduced into the instrument. A dynamic range of measurable (3)He/(4)He ratios with He-MS is greater than 10(3) which was determined by measuring various types of natural fluid samples from continental gas (with a low (3)He/(4)He ratio down to 2×10(-8)) to volcanic gas (with a high (3)He/(4)He ratio up to 3×10(-5)). The accuracy and precision of (3)He/(4)He and (4)He/(20)Ne ratios were evaluated by comparing the values with those measured using well established noble gas mass spectrometers (modified VG5400/MS-III and -IV) in our laboratory, and were found to be in good agreement within analytical errors. Usefulness of the selective extraction of He from water/gas using a high permeability of He through a silica glass wall at high temperature (700°C) is demonstrated.
authors.affiliation: Geochemical Research Center, Graduate School of Science, The University of Tokyo.
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Bajo
authors.affiliation: Geochemical Research Center, Graduate School of Science, The University of Tokyo.
authors.forename: Hirochika
authors.initials: H
authors.lastname: Sumino
authors.affiliation: Project Research Center for Fundamental Sciences, Graduate School of Science, Osaka University.
authors.forename: Michisato
authors.initials: M
authors.lastname: Toyoda
authors.affiliation: Geochemical Research Center, Graduate School of Science, The University of Tokyo ; Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University.
authors.forename: Ryuji
authors.initials: R
authors.lastname: Okazaki
authors.affiliation: Geochemical Research Center, Graduate School of Science, The University of Tokyo ; Quantum Beam Science Directorate, Japan Atomic Energy Agency (JAEA).
authors.forename: Takahito
authors.initials: T
authors.lastname: Osawa
authors.affiliation: Department of Physics, Graduate School of Science, Osaka University.
authors.forename: Morio
authors.initials: M
authors.lastname: Ishihara
authors.affiliation: Department of Physics, Graduate School of Science, Osaka University.
authors.forename: Itsuo
authors.initials: I
authors.lastname: Katakuse
authors.affiliation: Geochemical Research Center, Graduate School of Science, The University of Tokyo.
authors.forename: Kenji
authors.initials: K
authors.lastname: Notsu
authors.affiliation: Geochemical Research Center, Graduate School of Science, The University of Tokyo.
authors.forename: George
authors.initials: G
authors.lastname: Igarashi
authors.affiliation: Geochemical Research Center, Graduate School of Science, The University of Tokyo.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Nagao
keywords: He extraction from natural fluids; monitoring of 3He/4He ratio; small-size mass spectrometer