Isotopic anomalies of noble gases in meteorites and their origins

Noble gases were analyzed by stepped heating in 5 fractions of a chemically resistant residue (0.27%) from Murchison that had been separated according to grain size and resistance to HClO4. Nine gas components were recognized, of which 3 appear to be presolar. None of the three presolar carriers shows a clear excess of He3 or Ne21 that could be attributed to a presolar irradiation. A new composition of s-Xe has been derived from 17 Murchison or Orgueil fractions enriched in this component. It is similar to an earlier estimate, and shows the characteristic dominance of isotopes 128, 130 and 132. The spectrum of s-Kr is more tentative, but shows a clear enrichment of Kr86. This indicates that the neutron capture lifetime for Kr85 during the s-process was comparable to its 10.76 yr β-decay half life. Components of solar-system origin include two varieties of Ne-A, differing in host phase, release temperature, 21/22 ratio, and associated Xe components. The high 21/22 ratio of Ne-A2 is responsible for the ostensible 'excesses' of spallogenic Ne21 in chromite-rich separates from Murchison and Allende. The ArKrXe components in Murchison ferrichromite could not be measured in pure form, due to contamination with polymer. However, mixing calculations suggest that they are identical to their counterparts in Allende. Apparently Murchison and Allende ferrichromite formed under very similar conditions, and hence have similar gas components, including CCFXe. (author)