Anomalous Rhenium Isotopic Ratio in the Solar Wind: Detection at the Nanogram Level

Abstract

CLAYTON¹ recently considered an apparent anomaly in the ¹⁸⁷Re–¹⁸⁷Os cosmochronology. He showed that this could be resolved if the half life of ¹⁸⁷Re was significantly shortened in a stellar environment, and considered the solution to lie in the bound beta decay process, which is energetically feasible for the weak ¹⁸⁷Re transition². The ionization of Re in the outer solar convective zone increases the number of vacant bound states available, and Clayton suggests a reduction in the total ¹⁸⁷Re half life from 43×10⁹ yr to about 3×10⁹ yr. It might therefore be expected that the ¹⁸⁷Re/¹⁸⁵Re ratio in the solar wind would be between one-half and one-third that observed terrestrially. Clayton proposed that the hypothesis could be tested by measuring the isotopic ratio of Re in the surface layer of an old part of the lunar regolith, and stressed that “this measurement should eventually be undertaken if there is any reasonable chance of detection”. In this article I suggest a simple sensitive method to detect the expected isotopic anomaly.