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

已灭绝的核素是存在于早期太阳系中的放射性核素，但由于半衰期短而完全衰变。然而，它们的子体核素经常在原始陨石如碳质陨石中被检测到同位素异常，这可以用于早期太阳系的年代学。我们在比尔兹利陨石中发现了Ba同位素异常，并认为这是由于已灭绝的核素Cs-135（半衰期2.3Ma）所致。本文试图确定Cs-135在早期太阳系中的存在，并将其应用于年代学研究。CI、CM、CR和CV族的碳质辉长岩大多同时出现Ba-135和Ba-137同位素异常，表明这些异常主要是由于S-过程和/或R-过程的核合成所致。另一方面，热蚀变的CK组碳质方解石和无球粒陨石没有显示出任何显着的异常。Ba同位素丰度在母岩中均质化，部分钡同位素异常中的r过程成分可被校正，Cs-135年代学表明形成年龄为7（+5/-2）Ma。这一年龄比Mn-53绝灭核素年代学测定的Cl碳酸盐形成年龄短，可能表明Ba在母体中的再分配。

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.