Strontium isotopic composition in individual circumstellar silicon carbide grains: A record of s-process nucleosynthesis

Twenty six individual circumstellar SiC grains extracted from the Murchison meteorite were analyzed for their strontium isotopic compositions by resonant ionization mass spectrometry. Large abundance deficits were found for the p-process isotope ⁸⁴Sr. The measured grains had ⁸⁷Sr/⁸⁶Sr ratios indistinguishable from the primordial solar value, but several grains differed in their ⁸⁸Sr/⁸⁶Sr ratios as a consequence of the branch point at ⁸⁵Kr. The Sr isotopic data are consistent with s-process nucleosynthesis at moderate neutron densities.