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Meteoritic abundances of r-process elements are analyzed to deduce thehistory of chemical enrichment by r-process from the beginning of diskformation to the present time in the solar vicinity, by combining the abundanceinformation from short-lived radioactive nuclei such as 244Pu with that fromstable r-process nuclei such as Eu. These two types of nuclei can be associatedwith one r-process event and cumulation of events till formation of the solarsystem, 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 solarsystem, (ii) the present-day low 244Pu abundance as measured in deep seareservoirs results from the low recent star formation rate compared to ~4.5 - 5Gyr ago, and (iii) there were ~15 r-process events in the solar vicinity fromformation of the Galaxy to the time of solar system formation and ~30 r-processevents to the present time. Then, adopting a reasonable hypothesis that aneutron star merger is the r-process production site, we find that the ejectedr-process elements are extensively spread out and mixed with interstellarmatter with a mass of ~3.5 million solar masses, which is about 100 timeslarger than that for supernova ejecta. In addition, the event frequency ofr-process production is estimated to be one per about 1400 core-collapsesupernovae, which is identical to the frequency of neutron star mergersestimated from the analysis of stellar abundances.

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