Using (, Xn) Reaction Rates and Abundance Ratios to Constrain the Weak R-Process

The lighter heavy elements of the first r-process peak, between strontium and silver, can be synthesized in the moderately neutron-rich neutrino-driven ejecta of either core-collapse supernovae or neutron star mergers via the weak r-process. This nucleosynthesis scenario exhibits uncertainties from the absence of experimental data from (alpha, xn) reactions on neutron-rich nuclei, which are currently based on statistical model estimates. We have performed a new impact study to identify the most important (alpha, xn) reactions that can affect the production of the lighter heavy elements under different astrophysical conditions and using new, constrained (alpha, xn) reaction rates based on the Atomki-V2 alpha OMP. We have identified a list of relevant reactions that affect elemental abundance ratios that can be compared to abundances from metal-poor stars. Our results show how when reducing the nuclear physics uncertainties, we can use abundance ratios to constrain the astrophysical conditions/environment. This will be possible with the planned experiments to measure key (alpha, xn) reaction rates using the SECAR recoil separator at FRIB that will also be briefly discussed.