Using excitation-energy dependent fission yields to identify key fissioning nuclei in r-process nucleosynthesis

The possibility that nucleosynthesis in neutron star mergers may reach fissioning nuclei introduces significant uncertainties in predicting the relative abundances of r-process material from such events. We evaluate the impact of using sets of fission yields given by the 2016 GEF code for spontaneous (sf), neutron-induced ((n, f)), and beta-delayed (beta df) fission processes which take into account the approximate initial excitation energy of the fissioning compound nucleus. We further explore energy-dependent fission dynamics in the r process by considering the sensitivity of our results to the treatment of the energy sharing and de-excitation of the fission fragments using the FREYA code. We show that the asymmetric-to-symmetric yield trends predicted by GEF 2016 can reproduce the high-mass edge of the second r-process peak seen in solar data and examine the sensitivity of this result to the mass model and astrophysical conditions applied. We consider the effect of fission yields and barrier heights on the nuclear heating rates used to predict kilonova light curves. We find that fission barriers influence the contribution of Cf-254 spontaneous fission to the heating at similar to 100 d, such that a light curve observation consistent with such late- time heating would both confirm that actinides were produced in the event and imply the fission barriers are relatively high along the Cf-254 beta-feeding path. We lastly determine the key nuclei responsible for setting the r-process abundance pattern by averaging over thirty trajectories from a 1.2-1.4 M-circle dot neutron star merger simulation. We show it is largely the odd-N nuclei undergoing (Z, N)(n, f) and (Z, N) beta df that control the relative abundances near the second peak. We find the 'hot spots' for beta-delayed and neutron-induced fission given all mass models considered and show most of these nuclei lie between the predicted N = 184 shell closure and the location of currently available experimental decay data.