An Attempt for Mineral Identification by Means of Secondary Ion Mass Spectrometry

在这个项目中，我们首先尝试寻找一组质谱图，以便在二次离子质谱仪(SIMS)的同位素分析过程中对造岩矿物进行同步表征。在将样品安装在SIM中之前，必须对样品表面进行抛光和清洗。通过这些过程，任何地面污染都无法避免。特别是观察到了与碱性元素对应的质谱峰。这些元素不能以化学计量的形式存在，但可能来自抛光粉或洗涤水。对于陆地岩石或矿物样品的同位素分析来说，这种污染并不是那么麻烦，因为质谱仪可以用通常的质量分辨率来分离这种同位素污染。然而，在矿物鉴定的情况下，需要重现矿物化学计量组成的质谱峰模式。此外，这种污染会导致…对于分析地外物质，如陨石，存在更严重的问题。为了对质谱图进行交叉检查，我们尝试建造一种新的质谱仪，它具有直接加载样品的表面电离离子源。我们将这种新型质谱仪命名为直接进样表面电离离子源质谱计(DLMS)。它没有受到陆地的污染。对于这种离子源，挑选出一小部分(约1毫克重量)的新鲜破碎样品，并直接装载在船上的钽丝上蒸发。然后，蒸发的原子通过表面电离被电离到Re灯丝的表面。在这里，样品装载过程中可能会发生陆地环境的表面污染。但与SIMS中抛光的样品相比，这种污染是表面的，在真空中预热几个小时就可以去除这种污染。用DLMS对含Li、B、Mg、Si、Ti等成岩矿物进行了同位素分析，并检查了特征质谱图。初步获得了矿物的质谱图与其化学成分之间可能的正相关关系。较少

During this project, we first tried to find the grouping of mass spectral patterns to take a simultaneous characterization for rock-forming minerals during isotopic analysis by means of secondary ion mass spectrometry (SIMS). It is necessary to polish and wash the sample surfaces before mounting it in SIMS.Any terrestrial contamination could not be avoided through these processes. Especially, mass spectral peaks corresponding to alkaline elements were observed. These elements could not be stoichiometrically present, but might be originated from polishing powder or washing water. Such a contamination is not so troublesome for the isotopic analysis of terrestrial rock or mineral samples, because mass spectrometer can separate this kind of isotpic contamination with usual mass resolving power. However, in case of mineral identification, the reproduction of mass spectral peak patterns for the stoichiometrical compositions of minerls is needed. Furthermore, this kind of contamination causes … More serious problems for the analysis of the extraterrestrial matter, for example meteorite.For the purpose of corss-checking of mass spectrum, we have attempted to construct a new mass spectrometer with a direct sample loading surface ionization ion source. We named this new type of mass spectrometer "Direct sample Loding surface ionization ion source Mass Spectrometer (DLMS)." It is free from terrestrial contamination. For this ion source, a small portion (about 1mg weight) of fresh broken sample is picked out, and is directly loaded on a boat filament of tantalum for evaporation. Then, evaporated atoms are ionized on the surface of rhenium flament by surface ionization. Here the surface contamination from terrestrial environment during sample loading can happen. But this contamination is surfacial as compared to the polished sample in SIMS,and it can be removed by preheating the sample in vacuum for a few hours.With DLMS,rock-forming minerals containing Li, B,Mg, Si, Ti etc.were isotopically analyzed and checked for characteristic mass spectral patterns. We have preliminarily obtained the possible positive correlations between mass spectral patterns of the minerals and their chemical compositions. Less