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                          森羅万象セミナー  第 62 回
                   http://www.ep.sci.hokudai.ac.jp/~sinra/

                                 中村栄三
                      (岡山大学固体地球研究センター)

     『サンプルリターンを念頭に置いた極微小量試料の総合的地球化学分析』

                   日時：12 月 18 日 (火) 17：00 -- 18:30
                   場所：5 号館 201 号室

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[講演要旨]

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.