Radioactive Cs capture in the early solar system

Barium isotopic compositions of primitive materials in the solar system are generally affected by s- and r-process nucleosynthetic components that hide the contribution of the isotopic excess of (135)Ba formed by decay of radioactive (135)Cs. However, the Ba isotopic composition of the chemical separates from chondrules in the Sayama CM2 chondrite shows an excess of (135)Ba isotopic abundance up to (0.33 ± 0.06)%, which is independent of the isotopic components from s- and r-process nucleosyntheses. The isotopic excesses of (135)Ba correlate with the elemental abundance of Ba relative to Cs, providing chemical and isotopic evidence for the existence of the presently extinct radionuclide (135)Cs (t(1/2) = 2.3 million years) in the early solar system. The estimated abundance of (135)Cs/(133)Cs = (6.8 ± 1.9) × 10(−4) is more than double that expected from the uniform production model of the short-lived radioisotopes, suggesting remobilization of Cs including (135)Cs in the chondrules of the meteorite parent body.