Allende meteorite: Isotopically anomalous xenon is accompanied by normal osmium.
The (184)Os/(190)Os ratio of six Allende meteorite samples was determined by neutron activation analysis. Four chromite concentrates gave a ratio differing from the terrestrial ratio by only -0.1 +/- 0.4%, although they contained highly anomalous xenon enriched by up to 67% in (124)Xe and 93% in (136)Xe. In view of this result and the normal isotopic composition of carbon and oxygen in these fractions, it seems very unlikely that the xenon anomalies were produced in a supernova by the p and r processes. More probably, the xenon anomalies were established in the early solar system, by mass fractionation during trapping of noble gases in solids and by spontaneous fission of a superheavy element.Two other samples, containing osmium from the calcium,aluminum-rich inclusions, also gave an (184)Os/(190)Os ratio within -0.1 +/- 0.5% of the terrestrial value, although these inclusions show well-established anomalies in the light elements oxygen and magnesium, which appear to be due to pre-solar dust grains of distinctive nuclear history. Apparently the stellar source of the anomalous oxygen and magnesium did not synthesize heavier elements.
Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637.
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Takahashi
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Higuchi
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Gros
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Morgan
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Anders