Where is the back scatter peak in simulated Cs-137 spectrum?

Hello. I’m simulating a CZT detector which is exposed to a Cs-137 radioactive source. I extracted an energy deposition spectrum and I found there was no back scatter peak. G4EmStandardPhysics is entailed in my PhysicsList, so Compton scattering is considered in my simulation model. I will appreciate it if anyone could help me.

Since you didn’t provide any details of your simulation, the most likely reason is that your world is too simplified. Consider that the backscatter peak arises when a gamma Compton scatters in some material and then deposits all of its remaining energy in the detector. If your simulation geomery is very simplified and contains only the CZT crystal, there is no other material in which the gamma can lose energy.

Thank you very much! Your analysis is correct. Since my simulation model is excessively simplified, all the backscatter photon-recoil electron pairs are generated in the detector. Therefore, both the energy of the electron and the photon contribute to the energy deposition in a relative event in principle, and that’s why I couldn’t see the back scatter peak before. Now I can see it after adding an Al film behind the detector.

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