Presolar grains in micro-inclusions of iron meteorites

Abstract

In residues of several iron meteorites, obtained by dissolution of the metal in dilute H₂SO₄, the isotopic ratio of ¹⁹⁰Os/¹⁸⁴Os has been measured by radiochemical neutron activation analysis and is found to be anomalous in several cases. The largest deviation so far seen is a 40% enrichment of ¹⁸⁴Os in a mineral of Sikhote Alin. A lack of homogenization of the two isotopes that are produced in different nucleosynthetic processes suggests that iron meteorites are more primitive than any other matter available to us so far. Isotopic composition of Xe is found to be planetary in general. However the two light isotopes ¹²⁴Xe and ¹²⁶Xe are strongly depleted in some non-magnetic residues. Correlation diagrams of isotopic ratio pairs indicate that a two component mixture model is not adequate. EPR studies of the non-magnetic fractions of the residues show a large concentration of stabilized free radicals which could be ascribed to an irradiation of micro-inclusions prior to compaction into the metal matrix.