Computer Science
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.550w&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 550
Computer Science
4
Breccia, Chemical Composition, Lunar Rocks, Mineralogy, Xenon Isotopes, Degassing, Etching, Plutonium Isotopes, Radioactive Age Determination
Scientific paper
Regolith breccia 14301 is one of the lunar samples that contain Pu-244-derived fission Xe and radiogenic Xe-129 in excess of what may be expected by in-situ production. The sample also contains trapped solar noble gases. Stepped heating and grain-size-suite studies indicate a surface siting of the 'parentless' fissiogenic and radiogenic Xe. The presence of these two components may indicate a very early trapping of the solar gases, possibly while the parentless Xe was still extant. Closed-system stepped etching (CSSE) may shed additional light on the siting of the various noble gas components. Previously we reported CSSE data of a gently crushed bulk sample of 14301. This gas release sequence indicated that the fission component is sited on the grain surfaces, in agreement with the earlier studies. We present data on two fractions enriched in plagioclase (Plag) and mafic minerals (Pyx) respectively. Both separates contained approximately 10-20% of aggregates of small grains. Both samples released Pu-244 fission Xe mixed with solar Xe. In both mineral fractions, the most fissiogenic Xe was observed towrd the end of the analyses, together with relatively large amounts of cosmogenic noble gases. The decoupling of solar and fissiogenic noble gases argues against the hypothesis that the former were trapped while the latter were still extant. Corrections for cosmogenic Xe are too uncertain to infer the radiogenic Xe-129 concentrations in most steps of both mineral fractions. The (Kr-84/Xe-132)sol ratio is nearly constant throughout the 'Pyx'. We interpreted such flat (Kr-84/Xe-132) patterns in Closed System Stepped Etching (CSSE) analyses to indicate negligible Kr/Xe fractionation in the sample, but a fractionation between solar source and solar corpuscular radiation. The (Kr-84/Xe-132)sol ratios similarly low as in 14301 are observed for samples with large antiquity.
Baur Holger
Wieler Rainer
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