Correlated strontium and barium isotopic compositions of acid-cleaned single mainstream silicon carbides from murchison

Abstract

We present strontium, barium, carbon, and silicon isotopic compositions of 61 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing both strontium and barium contamination. For the first time, by using correlated ⁸⁸Sr/⁸⁶Sr and ¹³⁸Ba/¹³⁶Ba ratios in mainstream SiC grains, we are able to resolve the effect of ¹³C concentration from that of ¹³C-pocket mass on s-process nucleosynthesis, which points toward the existence of large ¹³C pockets with low ¹³C concentrations in asymptotic giant branch stars. The presence of such large ¹³C pockets with a variety of relatively low ¹³C concentrations seems to require multiple mixing processes in parent asymptotic giant branch stars of mainstream SiC grains.