  The light curves of Type Ia Supernovae (SN Ia) are powered by gamma-rays
emitted by the decay of radioactive elements such as $^{56}$Ni and its decay
products. These gamma-rays are downscattered,absorbed, and eventually
reprocessed into the optical emission which makes up the bulk of all supernova
observations. Detection of the gamma-rays that escape the expanding star
provide the only direct means to study this power source for SN Ia light
curves. Unfortunately, disagreements between calculations for the gamma-ray
lines have made it difficult to interpret any gamma-ray observations.
  Here we present a detailed comparison of the major gamma-ray line transport
codes for a series of 1-dimensional Ia models. Discrepancies in past results
were due to errors in the codes, and the corrected versions of the seven
different codes yield very similar results. This convergence of the simulation
results allows us to infer more reliable information from the current set of
gamma-ray observations of SNe Ia. The observations of SNe 1986G, 1991T and
1998bu are consistent with explosion models based on their classification:
sub-luminous, super-luminous and normally-luminous respectively.
