Light-Element Reaction Flow and the Conditions for r-Process Nucleosynthesis

We deduce new constraints on the entropy per baryon ( s/k ), dynamical timescale ( τ 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 4 He(t, γ ) 7 Li(n, γ ) 8 Li( α ,n) 11 B significantly en-hances 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 two higher than previous estimates. This places new constraints on dynamical models for the r-process.