Detection of the extinct nuclides by the precise isotopic ratio measurements and chronology of the early solar system

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Extinct nuclides are radioactive nuclides which existed in the early solar system but decayed thoroughly due to their short half lives. However, their daughter nuclides are often detected as isotopic anomalies in primitive meteorites such as carbonaceous meteorites, and this can be used for chronology of the early solar system. We have found the Ba isotopic anomaly in the Beardsley meteorite and suggested that this is due to the extinct nuclide Cs-135 (half life 2.3Ma). In the current study, we try to establish the existence of Cs-135 and apply it for chronology in the early solar systemWe measured the barium isotopic abundances in various meteorites, especially carbonaceous chondrites. Most carbonaceous chondrites of CI, CM, CR and CV groups show the Ba-135 and Ba-137 isotopic anomalies simultaneously, which imply that these anomalies are mainly due to nucleosynthesis of s-process and/or r-process. On the other hand, thermally-altered CK group carbonaceous chondrites and achondrites do not show any significant anomalies. Their Ba isotopic abundances could be homogenized at their parent bodies.Part of the r-process components in the barium isotopic anomalies of CM chondrites could be corrected and the Cs-135 chronology suggests the formation age of 7 (+5/-2) Ma. This age is shorter than the formation age of CI carbonates by Mn-53 extinct nuclide chronology and may suggest the re-distribution of Ba at the parent bodies.