NITROGEN ISOTOPE GEOCHEMSITRY AT NANO-MOLE LEVEL

我们改进了稀有气体质谱仪，用于亚纳米摩尔水平的氮同位素测量。建立了低本底高真空线，用于岩石和气体样品中氮气和氩气的分离纯化。1996年，我们开始了用惰性气体质谱仪测量氮同位素的基础实验。我们还调整了广岛大学已经安装的用于地下水和火山气体研究的氦同位素质谱仪。用另一条真空线从样品中分离二氧化碳。1997年，我们成功地测量了*O的氮同位素。3%使用亚纳摩尔样品。这是当时世界上最好的分析系统。利用另一种真空线和质谱仪同时对地下水样品进行氦同位素和氚的分析。这些资料对研究沉积盆地地下水的成因和演化具有重要意义。1998年，我们利用质量管理体系开发了氩气测量系统。利用该系统，我们可以分析火山气体样品中的氩同位素和氦丰度，以及氮和氦同位素。我们还改进了高真空球磨机对岩石样品的抽气系统，该系统适用于低氮丰度海洋玄武岩玻璃样品。该系统获得了几个重要的结果，并发表在国际期刊上。

We have improved noble gas mass spectrometer for nitrogen isotope measurement at sub-nano mole level. Low background high vacuume line was constracted for separation and purification of nitrogen and argon from rock and gas samples. In 1996, we started basic experiment of nitrogen isotope measurements using noble gas mass spectrometer. We also adjuested helium isotope mass spectrometer already installed at Hiroshima University for groundwaater and volcanic gas research. Separation of carbon dioxide from the samples was conducted using another vacuum line. In 1997, we succeeded in nitrogen isotope measurements at*O.3% using sub-namo mole sample. This is the best analytical system in the world at the time. Helium isotope and tritium analysis of groundwater samples were made at the same time using another vacuum line and mass spectrometer. These data are important for origin and evolution of groundwater in sedimentary basin. In 1998, we have developed argon measurement system using QMS.Bayed on the system, we could analyze argon isotopes and helium abundances in volcanic gas samples in addition to nitrogen and helium isotopes. We also improved gas extraction system from rock samples using a high vacuum ball mil. This is good for oceanic-basalt glass samples with low nitrogen abundances. Several important results were obtained by the system and they were published in international journals.