Heavy p-process nuclides in early solar system materials

在我们的太阳系中，所有比铁重的元素的同位素清单主要由核合成的r和s过程同位素组成。这些同位素是最丰富的，它们在早期太阳系物质中表现出相当均匀的同位素组成。我们的建议侧重于所谓的重p过程同位素，这是太阳系中最稀有的稳定同位素之一，反映了它们在超新星中特定的恒星形成条件。因此，可以预期它们的丰度可能会有很大的变化，但它们的丰度很低，迄今为止无法进行足够精确的测量。我们现在首次开发了分析方案，可以在epsilon水平上对重p过程同位素进行足够精确的丰度测量。在第一个资助阶段，我们专注于180W，并开始开发174Hf和180Ta的分析方案。对岩浆铁陨石（一些最古老的太阳系物质）180W丰度的测量显示，180W的大量过剩最初被解释为反映了早期太阳系不同程度的同位素均质化。然而，我们对球粒陨石和年轻分化陨石中的174Hf的测量没有显示出这种非均质性。我们随后可以证明180W的过剩在很大程度上可以用1840o的α衰变来解释。在项目的最后阶段，我们将继续开发分析方案，允许在同一样品分裂上组合测量p过程中的168Yb， 162Er-164Er， 180Ta和190Pt。这些数据将补充现有的重p过程同位素180W和174Hf的数据，从而允许评估p过程同位素的核合成模型和超新星物质注入新生太阳系的模型。将特别关注酸浸出液和不平衡球粒陨石的残留物，以便确定异常p过程同位素特征的潜在载体相。

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.