StefanoSpataro Messages: 2736 Registered: June 2005 Location: Torino
first-grade participant
From: *to.infn.it
I suppose not exactly the same.
In any case, the peak around 1 is your primary photon while the low energetic part comes from secondries and split-off. You can get rid of it with a simple energy cut. The position of the peak depends on the calibration.