I am trying to simulate galactic photon interactions in excess of 1 GeV, so I was wondering if there was a specific energy limit that cannot be simulated beyond. I know I get a warning at 20 MeV for neutron transport but am not sure if that applies to photons.
Also, something else- When modeling a silicon wafer exposed to about 1 keV photons, I was reading tallies for pair-production, so not really sure whats happening there.