Development of High Precision ^(238)U/^(235)U Ratio Measurements for Cosmochemical Applications

Abstract

Observations of variations in the ^(238)U/^(235)U ratio at the 0.1‰ level in both terrestrial [1] and meteoritic samples [e.g. 2-5], challenged the assumption of a constant ^(238)U/^(235)U ratio throughout the solar system (SS). The light isotopic compositions measured in some CAIs could be due to the presence of live ^(247)Cm in the early SS as this short-lived radionuclide decays into ^(235)U with a half-life t_(1/2)=15.6Myr. The most immediate consequence of these variations is that the isotopic composition of uranium has to be measured in each CAI to get accurate Pb-Pb ages [5,6]. Given the scale of the variations, achieving high precision measurements is necessary to fully resolve compositional differences between samples and to be able to use the potential of the U isotopic system in terrestrial and extraterrestrial samples.