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Description
We present new, mass-independent, Ni isotope data for a range of bulk chondritic meteorites. The data are reported as {epsilon}g^60^Ni_58/61_, {x3b5}^62^Ni_58/61_, and {epsilon}g^64^Ni_58/61_, or the parts per ten thousand deviations from a terrestrial reference, the NIST SRM 986 standard, of the ^58^Ni/^61^Ni internally normalized ^60^Ni/^61^Ni, ^62^Ni/^61^Ni, and ^64^Ni/^61^Ni ratios. The chondrites show a range of 0.15, 0.29, and 0.84 in {epsilon}g^60^Ni_58/61_, {x3b5}^62^Ni_58/61_, and {epsilon}g^64^Ni_58/61_ relative to a typical sample precision of 0.03, 0.05, and 0.08 (2 s.e.), respectively. The carbonaceous chondrites show the largest positive anomalies, enstatite chondrites have approximately terrestrial ratios, though only EH match Earth's composition within uncertainty, and ordinary chondrites show negative anomalies. The meteorite data show a strong positive correlation between {epsilon}g^62^Ni_58/61_ and {x3b5}^64^Ni_58/61_, an extrapolation of which is within the error of the average of previous measurements of calcium-, aluminium-rich inclusions. Moreover, the slope of this bulk meteorite array is 3.003+/-0.166 which is within the error of that expected for an anomaly solely on ^58^Ni. We also determined to high precision (~10 ppm per AMU) the mass-dependent fractionation of two meteorite samples which span the range of {epsilon}g^62^Ni_58/61_ and {x3b5}^64^Ni_58/61_. These analyses show that "absolute" ratios of ^58^Ni/^61^Ni vary between these two samples whereas those of ^62^Ni/^61^Ni and ^64^Ni/^61^Ni do not. Thus, Ni isotopic differences seem most likely explained by variability in the neutron-poor ^58^Ni, and not correlated anomalies in the neutron-rich isotopes, ^62^Ni and ^64^Ni. This contrasts with previous inferences from mass-independent measurements of Ni and other transition elements which invoked variable contributions of a neutron-rich component. We have examined different nucleosynthetic environments to determine the possible source of the anomalous material responsible for the isotopic variations observed in Ni and other transition elements within bulk samples.
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