Neutron capture rates in the r-process: the role of direct radiative capture1

The nuclear physics associated with neutron capture along the r-process path is reviewed, and it is noted that the usual statistical assumptions for the capture rates may not be valid. A comparison with statistical model calculations reveals that direct radiative capture may be the dominant reaction mechanism in the vicinity of and beyond the r-process path. The fact that the direct radiative capture mechanism represents a firm lower to the nuclear cross section is used to infer an upper limit of 1.5 x 1020 cm-3 for the critical neutron density necessary to guarantee (n,UPSILON) equilibrium in the r-process