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Thomas Trueman (Hull)

The Galactic Chemical Evolution of Radioactive Isotopes with an s-process Contribution
When Dec 16, 2021
from 03:45 PM to 04:00 PM
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Analysis of inclusions in primitive meteorites reveals that several short-lived radionuclides (SLRs) with half-lives 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 modelled 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 formation of AGB progenitor gamma, we calculate timescales relevant for the birth of the Sun. If tau/gamma > 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 107-Pd/182-Hf 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 < 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_sun Z=0.01 Monash model we find a self-consistent solution of T_LE=25.5 Myr.