  Neutron production via ^{4}He breakup and p(p, n{pi}^+)p is considered in the
innermost region of an accretion disk surrounding a Kerr Black Hole. These
reactions occur in a plasma in Wien equilibrium, where (radiatively produced)
pair production equals annihilation. Cooling of the disk is assumed to be due
to unsaturated inverse Comptonization of external soft photons and to the
energy needed to ignite both nuclear reactions. Assuming matter composition of
90% Hydrogen and 10% He, it is shown that, close to the border of this region,
neutron production is essentially from ^{4}He breakup. Close to the horizon,
the contribution from p(p, n{pi}^+)p to the neutron production is comparable to
that from the breakup. It is shown that the viscosity generated by the
collisions of the accreting matter with the neutrons may drive stationary
accretion, for accretion rates below a critical value. In this case, solution
to the disk equations is double-valued and for both solutions protons
overnumber the pairs. It is claimed that these solutions may mimic the states
of high and low luminosity observed in Cygnus X-1 and related sources. This
would be explained either by the coupling of thermal instability to the
peculiar behavior of the viscosity parameter alpha with the ion temperature
that may intermittently switch accretion off or by the impossibility of a
perfect tuning for both thermal and pair equilibrium in the disk, a fact that
forces the system to undergo a kind of limit cycle behavior around the upper
solution.
