[Gate-users] Inconsistent energy spectra with multiple sources

[Débora Salvado]

Dear GATE users

I have a SPECT setup as exemplified in the attached file setup.png

I run different simulations:
1) I123 (159 and 529keV) 185MBq in the patient volume
2) Lu176 (88, 200 and 300keV) 5.6MBq in the LSO volume
3) I123 185MBq and Lu176 5.6MBq in the respective volumes

In the file energySpectra.png, I show you the energy spectra obtained when
running every simulation for 1 minute. Can someone explain me why the
dashed and the black energy spectra are different?
The dashed spectrum is just a sum of the red and green data series.

In my opinion, the proportion of the peaks in the black spectrum seems
correct (simulation with both sources), but then why doesn't it correspond
to the sum of the counts obtained in separate simulations with only one of
the sources?

Any suggestions?

Regards,
Débora

Debora Salvado, MSc
PhD Student
University College London
INM, UCLH, (T-5) 235 Euston Road
London NW1 2BU
UK
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