The preliminary cosmic diffuse γ-ray spectrum from 800 keV to 30 MeV measured with COMPTEL

We report a preliminary Cosmic Diffuse 7-ray (CDG) spectrum from 800 keV to 30 MeV obtained with the COMPTEL instrument, the Imaging Compton Telescope onboard the Compton Gamma Ray Observatory. The spectrum is constructed by measuring the count rate of 7 rays from high galactic latitudes and first extrapolating the rate to a zero cosmic-ray flux environment to eliminate the prompt background. The prompt background is produced primarily by the interactions of protons and neutrons with the spacecraft. Second, this rate is then corrected for the effects of delayed internal radioactivity to arrive at the 7-ray count rate due to the CDG radiation. The preliminary measurements of the CDG flux in the 2-10 MeV range is 5-10 times lower than earlier reports. The 2-30 MeV flux is consistent with power-law extrapolations from lower and higher energies. The preliminary measurements show no evidence of a 'MeV bump' above 2 MeV. The bump, if present, is restricted to energies less than ~ 2 MeV.