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Oral Sessions
Day 3, June 24（Tue.） 16:45-17:00
Room B (Maesato Center)
- 3B-O3-1645
Improvement of sensitivity of electron ionization source for noble gas mass spectrometer using ion beam focusing by electrostatic quadrupole lenses
(Univ. Tokyo)
oHirochika Sumino
Although noble gas isotopes are powerful tracers in geosciences, their extremely low abundances in mineral and rock samples make their analysis quite difficult. We report an attempt of improvement of sensitivity of a noble gas mass spectrometer by installation of a new electron ionization (EI) source (Giese-type source).
The Giese-type EI source is equipped with two electrostatic quadrupole lenses. 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. 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°C to reduce outgas from the source materials. By using the new source, a sufficient mass resolution over 510 essential for 3He/4He analysis has been achieved with an improved sensitivity approximately three times higher than the previous condition. The improved mass spectrometer has enabled us to determine 3He/4He ratios of various mineral samples derived from the Earth's deep interior, such as diamonds or mantle-derived peridotites, to detect mantle plume ascending from the bottom of the mantle.