# Chemical evolution of 244Pu in the solar vicinity and its implication for the properties of r-process production

## TL;DR

This study uses meteoritic data and star formation history to trace the chemical evolution of 244Pu, revealing the timing of r-process events, their frequency, and implications for neutron star mergers as the primary r-process site.

## Contribution

It provides a novel analysis linking meteoritic abundances with galactic chemical evolution, estimating r-process event timing, frequency, and mixing scale, supporting neutron star mergers as key sources.

## Key findings

- The last r-process event occurred 130-140 Myr before solar system formation.
- Low current 244Pu abundance results from decreased recent star formation.
- Approximately 15 r-process events occurred before solar system formation, and about 30 till now.

## Abstract

Meteoritic abundances of r-process elements are analyzed to deduce the history of chemical enrichment by r-process from the beginning of disk formation to the present time in the solar vicinity, by combining the abundance information from short-lived radioactive nuclei such as 244Pu with that from stable r-process nuclei such as Eu. These two types of nuclei can be associated with one r-process event and cumulation of events till formation of the solar system, respectively. With help of the observed local star formation history, we deduce the chemical evolution of 244Pu and obtain three main results: (i) the last r-process event occurred 130-140 Myr before formation of the solar system, (ii) the present-day low 244Pu abundance as measured in deep sea reservoirs results from the low recent star formation rate compared to ~4.5 - 5 Gyr ago, and (iii) there were ~15 r-process events in the solar vicinity from formation of the Galaxy to the time of solar system formation and ~30 r-process events to the present time. Then, adopting a reasonable hypothesis that a neutron star merger is the r-process production site, we find that the ejected r-process elements are extensively spread out and mixed with interstellar matter with a mass of ~3.5 million solar masses, which is about 100 times larger than that for supernova ejecta. In addition, the event frequency of r-process production is estimated to be one per about 1400 core-collapse supernovae, which is identical to the frequency of neutron star mergers estimated from the analysis of stellar abundances.