Bizarre output from simulation

Hello everyone,

I’ve made a Geant4 simulation of a NaI spectrometer, but it seems that the output is incorrect. Below is a histogram from a 500MeV photon beam fired directly into the NaI crystal.

What troubles me about the data is the massive spike in events at 500MeV, as well as the dip just before that spike. It also appears as if there is another spike just before the dip in events.

I edited the example B4c to make my simulation if that helps at all.

I was wondering if anyone else has experienced issues like this, or might have any insight as to what the issue is.