2004ApJ...606.1006P

We consider nucleosynthesis in outflows originating from the inner regions of viscous accretion disks formed after the collapse of a rotating massive star. We show that windlike outflows driven by viscous and neutrino heating can efficiently synthesize Fe group elements moving at near-relativistic velocities. The mass of ⁵⁶Ni synthesized and the asymptotic velocities attained in our calculations are in accord with those inferred from observations of SN 1998bw and SN 2003dh. These steady windlike outflows are generally proton-rich, characterized by only modest entropies, and consequently synthesize essentially nothing heavier than the Fe group elements. We also discuss bubble-like outflows resulting from rapid energy deposition in localized regions near or in the accretion disk. These intermittent ejecta emerge with low electron fraction and are a promising site for the synthesis of the A=130 r-process peak elements.