  Solutions to the energy-independent (gray) radiative transfer equations are
compared to results of Monte Carlo simulations of the \Ni and \Co radioactive
decay \GR energy deposition in supernovae. The comparison shows that an
effective, purely absorptive, gray opacity, \KG $\sim (0.06 \pm 0.01)Y_e$
cm$^2$ g$^{-1}$, where $Y_e$ is the total number of electrons per baryon,
accurately describes the interaction of \GRs with the cool supernova gas and
the local \GR energy deposition within the gas. The nature of the \GR\
interaction process (dominated by Compton scattering in the relativistic
regime) creates a weak dependence of \KG on the optical thickness of the
(spherically symmetric) supernova atmosphere: The maximum value of \KG applies
during optically thick conditions when individual \GRs undergo multiple
scattering encounters and the lower bound is reached at the phase characterized
by a total Thomson optical depth to the center of the atmosphere \te \LA 1. Our
results quantitatively confirm that the quick and efficient solution to the
gray transfer problem provides an accurate representation of \GR energy
deposition for a broad range of supernova conditions.
