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 of Pd-107, Cs-135, and Hf-182, which are produced by slow neutron captures (the s-process) in asymptotic giant branch (AGB) stars. We modeled the Galactic abundances of these SLRs using the OMEGA+ 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-life tau of the SLR to the average length of time between the formations of AGB progenitors gamma, we calculate timescales relevant for the birth of the Sun. If tau/gamma greater than or similar to 2, we predict self-consistent isolation times between 9 and 26 Myr by decaying the GCE predicted Pd-107/Pd-108, Cs-135/Cs-133, and Hf-182/Hf-180 ratios to their respective ESS ratios. The predicted Pd-107/Hf-182 ratio indicates that our GCE models are missing 9%-73% of Pd-107 and Pd-108 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. If tau/gamma less than or similar to 0.3, we calculate instead the time (T (LE)) 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 2 M (circle dot), Z = 0.01 Monash model we find a self-consistent solution of T (LE) = 25.5 Myr.

Automated summary

Analysis of inclusions in primitive meteorites reveals the existence of short-lived radionuclides with half-lives of 0.1-100 Myr in the early solar system. This study investigates the origin of these radionuclides and their formation in the early solar system using galactic chemical evolution modeling.