  We follow the nuclear reactions that occur in the accretion disks of stellar
mass black holes that are accreting at a very high rate, 0.01 to 1 solar masses
per second, as is realized in many current models for gamma-ray bursts (GRBs).
The degree of neutronization in the disk is a sensitive function of the
accretion rate, black hole mass, Kerr parameter, and disk viscosity. For high
accretion rates and low viscosity, material arriving at the black hole will
consist predominantly of neutrons. This degree of neutronization will have
important implications for the dynamics of the GRB producing jet and perhaps
for the synthesis of the r-process. For lower accretion rates and high
viscosity, as might be appropriate for the outer disk in the collapsar model,
neutron-proton equality persists allowing the possible synthesis of 56Ni in the
disk wind. 56Ni must be present to make any optically bright Type Ib supernova,
and in particular those associated with GRBs.
