Element abundance patterns in stars indicate fission of nuclei heavier than uranium
Beers, Timothy C.; Placco, Vinicius M.; Holmbeck, Erika M.; Hansen, Terese T.; Roederer, Ian U.; Ezzeddine, Rana; Sakari, Charli M.; Frebel, Anna; Cowan, John J.; Vassh, Nicole; Mumpower, Matthew R.; Surman, Rebecca
United States, Canada, Sweden
Abstract
The heaviest chemical elements are naturally produced by the rapid neutron-capture process (r-process) during neutron star mergers or supernovae. The r-process production of elements heavier than uranium (transuranic nuclei) is poorly understood and inaccessible to experiments so must be extrapolated by using nucleosynthesis models. We examined element abundances in a sample of stars that are enhanced in r-process elements. The abundances of elements ruthenium, rhodium, palladium, and silver (atomic numbers Z = 44 to 47; mass numbers A = 99 to 110) correlate with those of heavier elements (63 ≤ Z ≤ 78, A > 150). There is no correlation for neighboring elements (34 ≤ Z ≤ 42 and 48 ≤ Z ≤ 62). We interpret this as evidence that fission fragments of transuranic nuclei contribute to the abundances. Our results indicate that neutron-rich nuclei with mass numbers >260 are produced in r-process events.