日本質量分析学会 第67回質量分析総合討論会

Abstract

Oral Sessions

Day 1, May 15(Wed.) 15:45-16:05 Room D (202)

Improvement of Sensitivity of a Multi-Turn Time-of-Flight Mass Spectrometer towards On-Site Helium Isotope Analysis of Volcanic and Hot Spring Gases

(Univ. Tokyo)
oHirochika Sumino, Yoshihide Akiyama

Helium isotope ratio (3He/4He) of volcanic gases/hot springs around a volcano has great potential for monitoring magmatic activity, because when magma becomes active, the 3He/4He ratios of nearby volcanic gases/hot springs may change as the relative contribution of magmatic helium to crustal one is expected to be higher. However, magnetic-sector mass spectrometry is used to measure 3He/4He currently, because adequate mass resolution to discriminate 3He+ from HD+ and a high-vacuum line to purify and separate helium from other gaseous species are required to measure 3He/4He ratios, resulting in that helium isotope analysis is limited to a suitable laboratory, and on-site, real-time monitoring of 3He/4He around a volcano is almost impossible.
We have been developing a new technique of noble gas analysis with “infiTOF” (infiTOF-UHV, MSI-Tokyo, Inc., Tokyo, Japan), which is a small, portable, multi-turn time-of-flight mass spectrometer, in order to monitor 3He/4He ratio in volcanic gas on site. The sensitivity of a normal infiTOF is not high enough to analyze noble gases in volcanic gas because most of the noble gas molecules admitted to the infiTOF are pumped out by a vacuum pump before ionized by an electron ionization source. To increase ionization efficiency by suppressing the number of exhausted gas molecules, we installed a gate valve between the ion source and pump and made a smaller aperture between the ion source and mass analyzer. Currently the 140 times sensitivity compared to that of a normal infiTOF has been achieved.