Report on noble gas isotopic compositions of the 1E and 2E samples: An example of noble gas analyses for small sample sizes

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Isotopic compositions and concentrations of noble gases were analyses for 1E and 2E samples. Two noble gas mass spectrometry systems were used for the analyses; MS-II for total melting and stepwise heating experiments on samples weighing 8-32 mg, and MS-III for laser heating using single or several grains weighing 3-40 micro g. Our data suggest that the sample 1E has noble gases similar to those for type 6 ordinary chondrites, while noble gases in 2E resemble those of carbonaceous chondrite Allende (CV3). Based on the present results we can conclude; 1) for ordinary chondritic materials several mg of sample is enough to measure all noble gas isotopes, 2) for surface materials of asteroids which would contain large amounts of implanted solar noble gases, the analytical technique using laser heating is applicable to samples weighing several micro g or less, 3) noble gas isotopic compositions obtained by the technique of single grain analysis can separate grains of different meteoroids impacted asteroidal surface, and 4) histories of exposure to cosmic-rays as well as impact degassing for each grain can provide detailed erosion process occurring on the asteroidal surface.
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