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Title: Galactic Chemical Evolution of Radioactive Isotopes with an s-process Contribution

Analysis of inclusions in primitive meteorites reveals that several short-lived radionuclides (SLRs) with half-lives of 0.1–100 Myr existed in the early solar system (ESS). We investigate the ESS origin of107Pd,135Cs, and182Hf, which are produced byslowneutron captures (thes-process) in asymptotic giant branch (AGB) stars. We modeled the Galactic abundances of these SLRs using theOMEGA+galactic chemical evolution (GCE) code and two sets of mass- and metallicity-dependent AGB nucleosynthesis yields (Monash and FRUITY). Depending on the ratio of the mean-lifeτof the SLR to the average length of time between the formations of AGB progenitorsγ, we calculate timescales relevant for the birth of the Sun. Ifτ/γ≳ 2, we predict self-consistent isolation times between 9 and 26 Myr by decaying the GCE predicted107Pd/108Pd,135Cs/133Cs, and182Hf/180Hf ratios to their respective ESS ratios. The predicted107Pd/182Hf ratio indicates that our GCE models are missing 9%–73% of107Pd and108Pd in the ESS. This missing component may have come from AGB stars of higher metallicity than those that contributed to the ESS in our GCE code. Ifτ/γ≲ 0.3, we calculate instead the time (TLE) from the last nucleosynthesis event that added the SLRs into the presolar matter to the formation of the oldest solids in the ESS. For the 2M,Z= 0.01 more » Monash model we find a self-consistent solution ofTLE= 25.5 Myr.

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The Astrophysical Journal
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Article No. 10
DOI PREFIX: 10.3847
Sponsoring Org:
National Science Foundation
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