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摘要
Rhenium is an important element with which to test hypotheses of isotope variation. Historically, it has been difficult to precisely correct the instrumental mass bias in thermal ionization mass spectrometry. We used W as an internal standard to correct mass bias on the MC-ICP-MS, and obtained the first precise delta Re-187 values (similar to +/- 0.02 parts per thousand, 2SE) for iron meteorites and chondritic metal. Relative to metal from H chondrites, IVB irons are systematically higher in delta Re-187 by similar to 0.14 parts per thousand. delta Re-187 for other irons are similar to H chondritic metal, although some individual samples show significant isotope fractionation. Since Re-185 has a high neutron capture cross section, the effect of galactic cosmic-ray (GCR) irradiation on delta(187) Re was examined using correlations with Pt isotopes. The pre-GCR irradiation delta Re-187 for IVB irons is lower, but the difference in delta Re-187 between IVB irons and other meteoritic metal remains. Nuclear volume-dependent fractionation for Re is about the right magnitude near the melting point of iron, but because of the refractory and compatible character of Re, a compelling explanation in terms of mass-dependent fractionation is elusive. The magnitude of a nucleosynthetic s-process deficit for Re estimated from Mo and Ru isotopes is essentially unresolvable. Since thermal processing reduced nucleosynthetic effects in Pd, it is conceivable that Re isotopic variations larger than those in Mo and Ru may be present in IVBs since Re is more refractory than Mo and Ru. Thus, the Re isotopic difference between IVBs and other irons or chondritic metal remains unexplained.
- 出版日期2017-3
