Recent advances in multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) have made it possible to resolve small differences in the 238U/235U isotope ratio, which was previously thought to be uniform for all Solar System materials. It has been shown for terrestrial samples that these differences are caused by isotope fractionation processes (primarily related to changes in the redox environment), concentrating the heavy isotope into the more reduced species. In calcium-aluminum-rich inclusions (CAIs), the recently reported excursions from the "normal" 238U/235U isotope ratio (=137.88) are primarily caused by the decay of the short-lived, r-process only isotope 247Cm (half life ~15.6 Ma) to 235U. It is proposed that a variety of bulk meteorites be investigated to: 1) establish the range of the 238U/235U ratios in Solar System materials, 2) determine if differences in the 238U/235U ratios in bulk meteorites are exclusively related to 247Cm decay in the early Solar System, or if they could be caused by other processes (e.g., redox variations, aqueous and thermal alteration etc.), and 3) re-calculate ages of Pb-Pb dated material for which a different 238U/235U ratio is measured with modern techniques than that previously assumed, focusing on meteorites that have been (or have the potential to be) used as age anchors for the application of short-lived chronometers.
|Effective start/end date||9/1/10 → 8/31/11|
- NASA: Goddard Space Flight Center: $29,785.00