Light-element reaction flow and the conditions for r-process nucleosynthesis

We deduce new constraints on the entropy per baryon (s/k), dynamical timescale (T_dyn), and electron fraction (Y_e) consistent with heavy-element nucleosynthesis in the r-process. We show that the previously neglected reaction flow through the reaction sequence ⁴He(t, γ)⁷Li(n, γ)⁸Li(α, n)¹¹B significantly enhances the production of seed nuclei. We analyze the r-process nucleosynthesis in the context of a schematic exponential wind model. We show that fewer neutrons per seed nucleus implies that the entropy per baryon required for successful r-process nucleosynthesis must be more than a factor of 2 higher than previous estimates. This places new constraints on dynamical models for the r-process.