Heavy p-process nuclides in early solar system materials

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Within our solar system, the isotope inventory of all elements heavier than Fe is mostly made up of nucleosynthetic r- and s-process isotopes. These isotopes are the most abundant ones, and they exhibit fairly uniform isotope compositions in early solar system materials. Our proposal focuses on the so-called heavy p-process isotopes that are among the rarest stable isotopes in the solar system which reflects their specific stellar formation conditions in supernovae. It can therefore be expected that their abundances may vary significantly, but their low abundances have hitherto made sufficiently precise measurements impossible. We now have developed for the first time analytical protocols that permit sufficiently precise abundance measurements of heavy p-process isotopes at the epsilon-level. During the first funding phase, we focused on 180W and started to develop analytical protocols for 174Hf and 180Ta. Measurements of 180W abundances in magmatic iron meteorites, some of the oldest solar system materials, revealed large excesses of 180W that were initially explained as reflecting different degrees of isotopic homogenisation in the early solar system. However, our measurements of 174Hf in chondrites and young differentiated meteorites did not show such heterogeneities. We could subesequently show that the 180W excesses are to a large extent explained by alpha decay of 184Os. In the final phase of the project we will continue to develop analytical protocols that allow combined measurements of p-process 168Yb, 162Er-164Er, 180Ta and 190Pt on the same sample split. These data will complement existing data for the heavy p-process isotopes 180W and 174Hf, thus permitting to evaluate nucleosynthetic models for p-process isotopes and models arguing for the injection of supernova material into the nascent solar system. A particular focus will be on acid leachates and residues of unequilibrated chondrites, in order to identify potential carrier phases of anomalous p-process isotope signatures.