Weak Charge‐changing Flow in Expandingr‐Process Environments

We assess the prospects for attaining steady nuclear flow equilibrium inexpanding r-process environments where beta decay and/or neutrino capturedetermine the nuclear charge-changing rates. For very rapid expansions, we findthat weak steady flow equilibrium normally cannot be attained. However, evenwhen neutron capture processes freeze out in such nonequilibrium conditions,abundance ratios of nuclear species in the r-process peaks might still mimicthose attained in weak steady flow. This result suggests that the r-processyield in a regime of rapid expansion can be calculated reliably only when allneutron capture, photodisintegration, and weak interaction processes are fullycoupled in a dynamical calculation. We discuss the implications of theseresults for models of the r-process sited in rapidly expanding neutrino-heatedejecta.Comment: 21 pages, AAS LaTex, 2 postscript figure