| アブストラクト |
We participated in the analytical competition related to the sample-return mission, MUSES-C of the ISAS to be launched in November 2002 and concluded in June 2006. In this competition, we determined as many major and trace element abundances and isotopes as possible, for both two powdered samples provided by ISAS and chondrules separated from Allende meteorite as an additional demonstration to show the analytical capabilities for small fragments.
100 mg of each the samples were split into two fractions of approximately 30 and 70 mg for the determinations of elemental abundances and the isotope analyses, respectively. The bulk concentrations of 55 elements in each 30 mg sample were analyzed using both quadruple-type ICP-MS and sector-type ICP-MS with analytical uncertainties better than 10 % (1s). Boron, Pb, Li, Rb, Sr, Sm and Nd were successively separated from each 70 mg of sample using some nearly developed integrated multi-ion exchange column chemistry, and then these isotopes were determined by TIMS with analytical errors similar to those obtained in our laboratory for terrestrial samples. Strontium, Nd, Re and Os isotopic compositions were also analyzed on remaining aliquots of the sample solutions used for trace element analyses by ICP-MS.
Chondrules were separated from Allende meteorite and then sliced into three pieces using a dicing saw. The center parts of the slices were used to determine mineral phases by compositional mapping and to obtain major and trace element compositions (30 elements) by a combination of optical microscopy, SEM-EDX and ion microprobe. The outer slices, for which sample sizes were < 1 mg, were chemically treated to obtain the bulk trace element and isotope compositions of chondrules. For these slices, 24 trace elements and Sr and Nd isotopic compositions were determined with extremely small analytical uncertainties using ICP-MS and TIMS, respectively. The analytical competition, using extremely small amounts of test samples has allowed a demonstration of the analytical capabilities of our geochemical laboratory, the PML, that could be applied to the samples to be returned from an asteroid by the MUSES-C mission. Most of the mineralogical and chemical data can be obtained for extremely small amounts of samples and with high spatial resolution. Japanese analytical capabilities will be further improved by repeating this type of competition and evaluation, and by incorporating other analytical techniques such as light element isotope analyses and age dating using ion and laser microprobes. Such improvements, aiming to analyze samples with extremely small sample sizes should also make it possible to obtain comprehensive mineralogical and geochemical analyses with high spatial resolution for precious samples returned from Mars. |
