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

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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