Simulation of spectrum is almost mono-energetic instead of broadly distributed

[franky180]

Trying to use the representation of a GE Healthcare NM 670 Discovery detector defined in opengate/contrib/spect_ge_nm670.py, I want to simulate a spectrum of a Tc-99m point source. For some reason the peak at 140.5 keV in the simulation seams to be almost mono-energetic (see Figure 1). Instead, I would expect a broader peak as measured with the actual physical system (see Figure 2). Is there a reason for the simulated peak not to be as broadly distributed? Comparing the simulated version to the actually measured one (see Figure 3) one can see that the peak area of the measurements is of the same magnitude as the simulated peak which gives reason to the assumption that the simulation is correct.

I attatched the code to simulate the spectrum mentioned above (GE_Healthcare_NM_670_Discovery_Simulations.py).

Figure 1: Simulation of a Tc-99m point souce with GE Healthcare NM 670 Discovery system.

Note: 3.7 MBq were reduced by a factor of 10 because of performance reasons in this case. Values: test000_NM_670_140.5 keV_370 kBq_60s.txt

Figure 2: Measurement of a Tc-99m souce with GE Healthcare NM 670 Discovery system.

Values: measurement_values.txt

Figure 3: Comparison between measurement and simulation.

[dsarrut]

Hello (first, sorry I did not see this message before). I think the digitizer is not correct here and should be adapted with additional modules (energy blurring etc). Maybe the best is to discuss by zoom (please send me an email).