NITROGEN ISOTOPE GEOCHEMSITRY AT NANO-MOLE LEVEL

我们改进了惰性气体质谱仪，用于亚纳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的分离提纯。1996年，我们开始了利用惰性气体质谱仪进行氮同位素测量的基础实验。我们还调整了广岛大学已经安装的氦同位素质谱仪，用于地面水和火山气体的研究。使用另一根真空管从样品中分离二氧化碳。1997年，我们利用亚那莫摩尔样品成功地进行了氮同位素测量，测量结果为0.3%。这是当时世界上最好的分析系统。用另一条真空线和质谱仪同时进行了地下水样品的氦同位素和氚分析。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QMS研制了Ar测量系统，在该系统的基础上，我们不仅可以分析氮和氦同位素，还可以分析火山气样品中的Ar同位素和氦丰度。我们还改进了使用高真空球磨机从岩石样品中提取气体的系统。这对氮丰度较低的大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.