Japan Geoscience Union Meeting 2015

Presentation information


Symbol S (Solid Earth Sciences) » S-GC Geochemistry

[S-GC51] Frontiers in noble gas isotope geosciences

Sun. May 24, 2015 4:15 PM - 6:00 PM A04 (APA HOTEL&RESORT TOKYO BAY MAKUHARI)

Convener:*Hironobu Hyodo(Research Institute of Natural Sciences, Okayama University of Science), Hirochika Sumino(Geochemical Research Center, Graduate School of Science, University of Tokyo), Takahiro Tagami(Graduate School of Science, Kyoto University), Chair:Hironobu Hyodo(Research Institute of Natural Sciences, Okayama University of Science), Hirochika Sumino(Geochemical Research Center, Graduate School of Science, University of Tokyo)

5:51 PM - 5:54 PM

[SGC51-P03] High sensitive noble gas mass spectrometer equipped with a Giese-type ion source

3-min talk in an oral session

*Hirochika SUMINO1, Keisuke NAGAO1 (1.GCRC, Grad. Sch. Sci., Univ. Tokyo)

Keywords:Noble gas, Mass spectrometer, Quadrupole lens, Ion source

Although noble gas isotopes are powerful tracers in geosciences, their extremely low abundances in mineral and rock samples make their analysis quite difficult. For example, concentration of 3He, which is a good indicator of mantle-derived component because of its primordial origin, is as high as 0.01 parts-per-trillion in volcanic rocks and mantle-derived materials. Such scarce noble gas isotopes are detected with a special mass spectrometer operated in static mode. We have made it possible to detect 103 to 104 atoms of noble gas isotopes by modifying a commercial sector-type single focusing noble gas mass spectrometer (VG5400), which is equipped with a double collector system to detect 3He and 4He simultaneously with a secondary electron multiplier and Faraday cup, respectively [1]. Here we report an attempt of further improvement of sensitivity of the mass spectrometer by installation of a new ion source (Giese-type source).
The Giese-type electron ionization (EI) ion source is equipped with two electrostatic quadrupole lenses [2]. This source has been reported to have up to two orders of magnitude higher sensitivity than conventional Nier-type EI source because of the absence of a beam defining slit to collimate the ion beam and thus high transmission [3]. We designed a Giese-type source to have an adequate resolution to separate 3He+ from HD+ and H3+, to have the source housing volume as small as possible, and to be bankable at up to 300℃ to reduce outgas from the source materials. The ion and electron optics were based on a calculation by Lu and Carr [4] and refined using SIMION-3D software [5]. Prior to the installation on the mass spectrometer, the ion beam profile emitted from the source was monitored by a microchannel plate and phosphor screen to optimize the configuration of the quadrupole lens.
A sufficient mass resolution over 500 essential for 3He/4He analysis has been achieved with an improved sensitivity approximately three times higher than the previous condition. The amount of helium required to obtain a precision with 3He/4He ratio is two orders of magnitude smaller than that with the condition installed by the manufacture. However, total ion transmission is estimated to be about 30%, suggesting further refinement of the source condition is required to obtain the maximum sensitivity.

References: [1] H. Sumino et al., J. Mass Spectrom. Soc. Jpn., 49, 61-68 (2001). [2] C.F. Giese, Rev. Sci. Instrum., 30, 260-261 (1959). [3] E.T. Kinzer and H. Carr, Rev. Sci. Instrum., 30, 1132 (1959). [4] C.-S. Lu and H.E Carr, Rev. Sci. Instrum., 33, 823-824 (1962). [5] D.A. Dahl, Int. J. Mass Spectrom., 200, 3-25 (2000).