  We present a new relativistic radiative-transfer code for $\gamma$-rays of
energy less than 5 MeV in supernova (SN) ejecta. This code computes the
opacities, the prompt emissivity (i.e. decay), and the scattering emissivity,
and solves for the intensity in the co-moving frame. Because of the large
expansion velocities of SN ejecta, we ignore redistribution effects associated
with thermal motions. The energy deposition is calculated from the energy
removed from the radiation field by scattering or photoelectric absorption.
This new code yields comparable results to an independent Monte Carlo code.
However, both yield non-trivial differences with the results from a pure
absorption treatment of $\gamma$-ray transport. A synthetic observer's frame
spectrum is also produced from the CMF intensity. At early times when the
optical depth to $\gamma$-rays is large, the synthetic spectrum show asymmetric
line profiles with redshifted absorption as seen in SN 2014J. This new code is
integrated within CMFGEN and allows for an accurate and fast computation of the
decay energy deposition in SN ejecta.
