A new approach to nucleocosmochronology

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Abstract
Arguments that the short-lived nuclides I-129 and Pu-244 in the solar system could have resulted from accretion of newly synthesized material when the presolar cloud last passed through a galactic arm are extended to the long-lived nuclides U-238 and Th-232. The time period during which the solar system accreted its r-process elements is calculated on the basis of the observed Th-232/U-238 isotopic abundance ratio. The free decay period for I-129 is computed, and the age of r-process elements is estimated to be 12.7 billion years. The cosmoradiogenic fractions of Os-187 and Sr-87 are determined, the free decay period is estimated to be 140 million years, and support for the analysis is obtained by computing the Pu-244/U-238 ratio in meteorites. It is suggested that the solar system may not have been an integral part of the galactic evolution process and that recently reported isotopic anomalies may have resulted from accretion of new elements during the collapse stage of the presolar cloud.

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