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1E-O5-1500 PDF
マルチターン飛行時間型質量分析計を用いた火山ガスおよびHESJ標準ガスのヘリウム同位体分析
Helium isotope ratio (3He/4He ratio) of volcanic gas has the potential as a monitoring tool of volcanic activity because it varies depending on contributions of magmatic and crustal helium. Although continuous analysis of volcanic gas is necessary to monitor volcanic activity, it is difficult because a large magnet-sector type mass spectrometer is currently used to analyze helium isotopes due to requirements for mass resolution and sensitivity. We have been developing a new technique of noble gas analysis using a portable multi-turn time-of-flight mass spectrometer (MULTUM). Since the sensitivity of a normal MULTUM was far lower than the requirement to analyze noble gases in volcanic gas, we installed valves between the spectrometer and the vacuum pumps to operate the mass spectrometer while it is isolated from the pumps. Besides, the ion counting method was introduced for signal processing. As a result, a significant number of 3He ions were detected during analyses of volcanic gas samples. 3He/4He ratios of volcanic gas samples, which were calibrated with the helium standard gas (HESJ), were consistent with those measured by a magnet-sector type mass spectrometer within analytical errors.