Abundances of Cosmic Ray Nuclei Heavier than _(50)Sn

Abstract

Preliminary results are reported from 430 days of exposure of the heavy nuclei experiment on the HEAO-3 spacecraft. These results are confined to the heavy nuclei with Z ≥ 50 and emphasize the conclusions obtained on the relative numbers of actinides and heavy stable elements in the lead-platinum region. The extreme paucity of actinides found is inconsistent with the predictions of a cosmic ray source that is highly enriched in r-process material, but quite consistent with a source whose composition is similar to that of normal solar system material. An upper limit, at the. 95% confidence level, is placed in the ratio of nuclei with Z ≥ 88/(74 ≤ Z ≤87) of 0.03.

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