NITROGEN ISOTOPE GEOCHEMSITRY AT NANO-MOLE LEVEL

我们改进了惰性气体质谱计，使其能在亚纳摩尔水平上测量氮同位素。采用低本底高真空线从岩石和天然气样品中分离提纯氮和氩。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。我们还调整了已安装在广岛大学的氦同位素质谱仪，用于地下水和火山气体研究。使用另一个真空管线从样品中分离二氧化碳。在1997年，我们成功地在 * 0.3%使用亚纳米摩尔样品的氮同位素测量。这是当时世界上最好的分析系统。利用另一条真空管和质谱仪同时对地下水样品进行氦同位素和氚分析。这些数据对沉积盆地地下水的起源和演化具有重要意义。1998年，我们研制了氩测量系统，在该系统上，除了氮、氦同位素外，还可以对火山气体样品进行氩同位素和氦丰度的分析。我们还改进了高真空球磨机的岩石样品气体提取系统，这对于低氮含量的海洋玄武岩玻璃样品是有利的。该系统取得了若干重要成果，并在国际期刊上发表。

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.