  It is widely believe that galactic cosmic rays are originated in supernova
remnants (SNRs) where they are accelerated by diffusive shock acceleration
process at supernova blast waves driven by expanding SNRs. In recent
theoretical developments of the diffusive shock acceleration theory in SNRs,
protons are expected to accelerate in SNRs at least up to the knee energy. If
SNRs are true generator of cosmic rays, they should accelerate not only protons
but also heavier nuclei with right proportion and the maximum energy of heavier
nuclei should be atomic mass (Z) times that of protons. In this work we
investigate the implications of acceleration of heavier nuclei in SNRs on
energetic gamma rays those are produced in hadronic interaction of cosmic rays
with ambient matter. Our findings suggest that the energy conversion efficiency
has to be nearly double for the mixed cosmic ray composition instead of pure
protons to explain the observation and secondly the gamma ray flux above few
tens of TeV would be significantly higher if cosmic rays particles can attain
energies Z times of the knee energy in lieu of 200 TeV, as suggested earlier
for non-amplified magnetic fields. The two stated maximum energy paradigm will
be discriminated in future by the upcoming gamma ray experiments like Cherenkov
Telescope array (CTA).
