Gamma Spectroscopy Using Germanium Detector

Dear all,

I simulated HPGe detector including the detector housing and the detector material. The simulation geometry is very simple, first, the source is an isotropic and monoenergetic (0.662MeV). The Germanium detector is ~3 cm away from the source. I want to get the spectrum of the detector. I tried by finding the energy deposition by the primary particle but I got very sharp peak at 0.662 MeV. So I changed the measured quantities in the code, I just recorded the number of electron/hole pairs created in the detector by counting the eIoni processes (as shown in Figure 1), I got low energy resolution (7%) compared to experimental spectrum. Next, I measured the total energy deposited by the ionized electrons (eIoni process) (Figure 2) but I got high resolution (0.06%). Any ideas what I should count to find the correct spectrum in such a simulation? examples other than Geant4 examples would be appreciated.

Gamma spectrum.pdf (177.0 KB)

Hello Ahmed,
I did exactly which you did and got the same result, did you get the solution of that?
for me I’m trying to use digitization of hits, because the digitization is the method to simulate the ADC outputs.
plz if you got the answer share it with me.
Thank you.


since you say simulation is very simple, I assume you’re not simulating the charge collection in the detector, that to my knowledge together with electronic noise, is the main responsible for resolution. Then what you get is the spectrum of the energy deposited in the crystal.

Rather than making a complete simulation what I usually do is to post process G4 spectra to redistribute the events energy according to observed resolution at a reference energy. I usually get good reproduction of measured spectra.