Construction of a Newly Designed Small-Size Mass Spectrometer for Helium Isotope Analysis : Toward the Continuous Monitoring of ^3He/^4He Ratios in Natural Fluids

Access this Article

Search this Article

Author(s)

    • BAJO Ken-ichi
    • Geochemical Research Center, Graduate School of Science, University of Tokyo
    • SUMINO Hirochika
    • Geochemical Research Center, Graduate School of Science, University of Tokyo
    • TOYODA Michisato
    • Project Research Center for Fundamental Sciences, Graduate School of Science, Osaka University
    • OKAZAKI Ryuji
    • Geochemical Research Center, Graduate School of Science, University of Tokyo
    • OSAWA Takahito
    • Geochemical Research Center, Graduate School of Science, University of Tokyo
    • ISHIHARA Morio
    • Department of Physics, Graduate School of Science, Osaka University
    • KATAKUSE Itsuo
    • Department of Physics, Graduate School of Science, Osaka University
    • NOTSU Kenji
    • Geochemical Research Center, Graduate School of Science, University of Tokyo
    • IGARASHI George
    • Geochemical Research Center, Graduate School of Science, University of Tokyo
    • NAGAO Keisuke
    • Geochemical Research Center, Graduate School of Science, University of Tokyo

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 (<sup>3</sup>He/<sup>4</sup>He) is described. The instrument is capable of measuring <sup>4</sup>He/<sup>20</sup>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 <sup>3</sup>He and <sup>4</sup>He with a double collector system under a mass resolution power (<i>M</i>/Δ<i>M</i>) of >500. The presently attained specifications of the He-MS are; (1) a mass resolving power of ca. 490, sufficient to separate <sup>3</sup>He<sup>+</sup> from interfering ions, HD<sup>+</sup> and H<sub>3</sub><sup>+</sup>, (2) ultra-high vacuum conditions down to 3×10<sup>−8</sup> Pa, and (3) a sufficiently high sensitivity to permit amounts of <sup>3</sup>He to be detected at levels as small as 10<sup>−13</sup> cm<sup>3</sup>STP (3×10<sup>6</sup> atoms). Long term stability for <sup>3</sup>He/<sup>4</sup>He analysis was examined by measuring the <sup>3</sup>He/<sup>4</sup>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<sup>−6</sup> cm<sup>3</sup>STP introduced into the instrument. A dynamic range of measurable <sup>3</sup>He/<sup>4</sup>He ratios with He-MS is greater than 10<sup>3</sup> which was determined by measuring various types of natural fluid samples from continental gas (with a low <sup>3</sup>He/<sup>4</sup>He ratio down to 2×10<sup>−8</sup>) to volcanic gas (with a high <sup>3</sup>He/<sup>4</sup>He ratio up to 3×10<sup>−5</sup>). The accuracy and precision of <sup>3</sup>He/<sup>4</sup>He and <sup>4</sup>He/<sup>20</sup>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.

Journal

  • Mass Spectrometry

    Mass Spectrometry 1, A0009, 2012-12-01

    The Mass Spectrometry Society of Japan

References:  26

Codes

Page Top