  We have studied the two-body production and decay of a heavy, right-handed
neutrino to two light states using the full Boltzmann equation instead of the
usual integrated Boltzmann equation which assumes kinetic equilibrium of all
species. Decays and inverse decays are inefficient for thermalising the
distribution function of the heavy neutrino and in some parameter ranges there
can be very large deviations from kinetic equilibrium. This leads to
substantial numerical differences between the two approaches. Furthermore we
study the impact of this difference on the lepton asymmetry production during
leptogenesis and find that in the strong washout regime the final asymmetry is
changed by 15-30% when the full Boltzmann equation is used.
