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Project Progress

A major research project under Task 1 is the identification and Pb-Pb dating of calcium-aluminum-rich inclusions (CAIs) containing fractionated unknown nuclear (FUN) effects. We have begun initial documentation of a suite of CAIs from the Allende and Vigarano carbonaceous chondrites (provided to us by Dr. Glenn MacPherson), with the goal of identifying possible candidates of FUN CAIs. We have additionally begun development of the analytical protocols for high-precision measurements of Ti isotopes by laser ablation and solution analyses in the Isotope Cosmochemistry and Geochronology Laboratory at ASU. The goal of this work will be to utilize Ti isotope compositions of CAIs as an indicator for the identification of FUN CAIs.

A second project, which has important implications for the Pb-Pb dating of FUN CAIs, relates to the investigation of uranium isotope variations in CAIs. High-precision Pb-Pb dating has relied on the assumption of an invariant ²³⁸U/²³⁵U ratio, and the goal of this investigation was to verify this assumption for meteoritic materials. Therefore, graduate student Greg Brennecka, working with PI Anbar and Co-I Wadhwa (and Prof. Stefan Weyer, U. Frankfurt, Germany) analyzed thirteen different CAIs from the Allende carbonaceous chondrite and have found variations of up to ~3.5 per mil in the ²³⁸U/²³⁵U ratio (relative to the terrestrial standard; Figure 1). These variations in the ²³⁸U/²³⁵U ratio correlate with Th/U and Nd/U ratios in these CAIs, suggesting that they are the result of decay of ²⁴⁷Cm in the early Solar System. This work was submitted for publication as a research article in Science and is currently in revision.