Stable nickel isotopes and cosmogenic beryllium-10 and aluminum-26 in metallic spheroids from Meteor Crater,Arizona

Abstract— The isotopic abundances of Ni in 17 metallic spheroids from Meteor Crater, Arizona, were determined by inductively coupled plasma mass spectrometry (ICP-MS). Sixteen spheroids have normal isotopic abundances. A 17th shows a marginally detectable mass fractionation of 0.40 ± 0.14 %/AMU in favor of the heavier isotopes. The general absence of mass fractionation indicates that open system evaporation caused little loss of Ni. Variable activities of the cosmogenic radionuclides ¹⁰Be and ²⁶Al were measured by accelerator mass spectrometry in separate suites of spheroids. Activities of ²⁶Al in most samples and of ¹⁰Be in metal cores separated from spheroids indicate that they either (1) come from greater depths in the parent meteoroid than do hand specimens, or (2) lost Al and Be during the process of spheroid formation. One individual spheroid has ¹⁰Be and ²⁶Al activities comparable to those of bulk specimens. This result suggests that spheroid formation may occasionally include material from the outermost meter or so of the impactor. Relatively high activities of ¹⁰Be, ～3 dpm/kg, in the siliceous shells of Canyon Diablo spheroids very likely have a meteoric origin.