Formation of the rare-earth peak: Gaining insight into late-time r-process dynamics

We study the formation and final structure of the rare-earth peak (A similar to 160) of the r-process nucleosynthesis. Under high-entropy conditions (S > 100k(B)), the rare-earth peak forms at late times in the r-process after neutron exhaustion (neutron-to-seed ratio R = 1) as matter decays back to stability. Since rare-earth peak formation does not occur during (n, gamma) (sic) (gamma, n) equilibrium it is sensitive to the strong interplay between late-time thermodynamic evolution and nuclear physics input. Depending on the conditions, the peak forms either because of the pattern of the neutron capture rates or because of the pattern of the separation energies. We analyze three nuclear data sets under different thermodynamic conditions. We find that the subtleties of each nuclear data set, including separation energies and neutron capture rates, influence not only the final shape of the peak but also when it forms. We identify the range of nuclei which are influential in rare-earth peak formation.