Turbulent mixing of r-process elements in the Milky Way

We study turbulent gas diffusion affects on r-process abundances in Milky Way stars, by a combination of an analytical approach and a Monte Carlo simulation. Higher r-process event rates and faster diffusion, lead to more efficient mixing corresponding to a reduced scatter of r-process abundances and causing r-process enriched stars to start appearing at lower metallicities. We use three independent observations to constrain the model parameters: (i) the scatter of radioactively stable r-process element abundances, (ii) the largest r-process enrichment values observed in any solar neighborhood stars, and (iii) the isotope abundance ratios of different radioactive r-process elements ((PU)-P-244/U-238 and Cm-247/U-238) at the early Solar system as compared to their formation. Our results indicate that the Galactic r-process rate and the diffusion coefficient are respectively r < 4 x 10(-5) yr(-1), D > 0.1 kpc(2) Gyr(-1) (r < 4 x 10(-6 )yr(-1), D > 0.5 kpc(2) Gyr(-1) for collapsars or similarly prolific r-process sources) with allowed values satisfying an approximate anticorrelation such that D approximate to r(-2/3), implying that the time between two r-process events that enrich the same location in the Galaxy, is tau(mix )approximate to 100-200 Myr. This suggests that a fraction of similar to 0.8 (similar to 0.5) of the observed Cm-247 (Pu-244) abundance is dominated by one r-process event in the early Solar system. Radioactively stable element abundances are dominated by contributions from similar to 10 different events in the early Solar system. For metal poor stars (with [Fe/H] less than or similar to -2), their r-process abundances are dominated by either a single or several events, depending on the star formation history.