2011ApJ...743..155S

We examine the prospects for producing nickel-56 from black hole accretion disks, by examining a range of steady-state disk models. We focus on relatively slowly accreting disks in the range of {dot}M = 0.05 M_☉/s to {dot}M = 1 M_☉/s, as are thought to be appropriate for the central engines of long-duration gamma-ray bursts. We find that significant amounts of nickel-56 are produced over a wide range of parameter space. We discuss the influence of entropy, outflow timescale, and initial disk position on mass fraction of nickel-56 which is produced. We keep careful track of the weak interactions to ensure reliable calculations of the electron fraction, and discuss the role of the neutrinos.