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标题：Iron and nickel isotopic compositions of presolar SiC grains from supernovae
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作者：E. Zinner ; S. Amari ; F. Gyngard 等
期刊名称：PoS - Proceedings of Science
印刷版ISSN：1824-8039
出版年度：2008
卷号：2008
出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：Approximately 1% of presolar SiC grains found in primitive meteorites condensed in the ejecta of Type II supernovae. To explain the isotopic signatures of these so-called X grains, material from different SN zones had to contribute to the mix from which the grains formed. We measured the Fe and Ni isotopic ratios of individual X grains with the NanoSIMS. Most grains have enhanced 57Fe/56Fe ratios ranging up to 2􀀁solar. A few grains have depleted 57Fe/56Fe ratios down to 0.55􀀁solar. In contrast, 54Fe/56Fe ratios are close to solar. Anomalies in the Ni isotopes are even more extreme. 61Ni/58Ni ratios range up to 3.5􀀁solar, 62Ni/58Ni ratios up to 2􀀁solar, but 60Ni/58Ni ratios only up to 1.1􀀁solar. One of the grains with 57Fe deficits has a 61Ni deficit, the others have normal 61Ni/58Ni ratios. The grain with the largest 57Fe deficit has 62Ni/58Ni of 1.8􀀁solar but solar 61Ni/58Ni. The excesses in 57Fe and 61,62Ni observed in most of the grains can be explained by admixture of material from the He/C zone to material from the He/N (or outer) zones. In the He/C zone, neutron capture results in 57Fe and 61,62Ni excesses, and the grain data can be fairly well reproduced by variable admixture from different layers of the He/C zone. The lack of large 54Fe excesses in the grains is puzzling in view of the fact that material from the Si/S zone, rich in 54Fe, is required to explain the 28Si excesses of X grains. We still do not have a good explanation for the 57Fe deficits of several of the grains; they could reflect the initial isotopic compositions of the parent stars.