Geocheminar spring-2012

The Solar System is a mixture of many different nucleosynthetic sources. Numerous studies have investigated the nucleosynthetic origins of the Solar System by examining isotopic anomalies in meteorites. Isotopic anomalies in the most neutron-rich isotopes of Ca, Ti, Cr in primitive meteorites have been interpreted as incomplete-mixing of a highly neutron enriched nucleosynthetic source into the early Solar System. This source has been variously hypothesised to be a type Ia supernova, type II supernova or an AGB star. However, nearly all of the reported measurements of these anomalies have employed normalisation to a pair of lighter-isotopes, assumed not to be anomalous. Hence, in these cases the inference of a neutron-rich anomaly is a point of interpretation since the anomaly could equally well reside on one of the normalising isotopes. More recently, Ni has been added to the list of elements exhibiting apparent anomalies in its most neutron-rich isotopes, 62Ni and 64Ni. We have made further measurements of Ni isotopes in bulk meteorites, both mass-independently (internally-normalised) and mass-dependently (double-spike), to yield absolute Ni isotope ratios that will better constrain the nucleosynthetic environment from which this incompletely mixed component arose. Our results show that, in fact, the anomalies reside on 58Ni and not on 62Ni or 64Ni.