I am currently struggling with Cs 137 spectrum. The best I could get is:
Comparing it to the correct spectrum, I clearly can see the backscatter peak, the Compton edge and the photopeak, however I have never seen the Ba x-rays line at 32 keV. Maybe there is an unobvious trick how to model it?
Currently I have a detector and a small disc filled with Cs 137. I simulate gamma particles from this disc with initial energy of 662 keV and collect data from scintillator. For simulation I use G4ParticleGun and QBBC as physics list.
As far as I know, QBBC is optimal in this case because it’s possibility to accurately work in energy regions of 20MeV and less, which is required. I’ve recently changed it to several others and have not seen any difference in results.