[Gate-users] Energy spectrum in simple CZT SPECT setup

[Philipp Matthies]

Hello,

I set up a very basic simulation with only a CZT crystal and a point source, nothing more. I'm using GATE v5 under Mac OS X.

In the screenshot I plotted a few variables from the Singles tree of the ROOT output. Can anybody explain the energy spectrum to me?
I didn't set any digitizer options and the source is monoenergetic (140.5keV) so I expected so see a clear photopeak at 140.5keV and the characteristic compton spectrum.
Instead there appear like two peaks between around 105keV and 115keV and a few more at lower energies. No photopeak, no compton spectrum, nothing like I expected it to be.

The setup was as followed:
- world volume 20 x 20 x 20 cm^3 air
- CZT crystal (4.0 x 4.0 x 0.5cm^3) set as sensitive detector
- point source of 140.5keV and 1MBq at a distance of 5cm centered in front of the crystal
- no digitizer

For the whole script with all variables set see attached file G4History.macro.


Kind regards,

Philipp Matthies

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Physics Department, TU Munich
Nuclear medicine, Klinikum rechts der Isar, Munich
SurgicEye GmbH, Munich

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