[Gate-users] non-uniform source distribution

[Enrico Clementel]

Dear Gate Users,
I'm modeling a Gemini TF scanner with a simple uniform water cylinder in it to test image reconstruction software. I'm using Gate 6.1 and saving to root output.
I kept seeing artifacts in the final image. Saving all the sources location in an image yields the following:
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There is clearly a higher concentration of sources in the phantom's center, the source intensity appears to be higher at the right side of the transaxial image and also note the diagonal line crossing the phantom in the coronal image.

Here is the macro section containing information about the source I'm using:

/gate/source/addSource bg
/gate/source/bg/setActivity 111000000 becquerel
/gate/source/bg/setType backtoback
/gate/source/bg/gps/particle gamma
/gate/source/bg/gps/energytype Mono
/gate/source/bg/gps/monoenergy 511 keV
/gate/source/bg/setForcedUnstableFlag true
/gate/source/bg/setForcedHalfLife 6586 s
/gate/source/bg/gps/angtype iso
/gate/source/bg/gps/type Volume
/gate/source/bg/gps/shape Cylinder
/gate/source/bg/gps/radius 175 mm
/gate/source/bg/gps/halfz 93 mm
/gate/source/bg/gps/centre 0. 0. 0. cm
/gate/source/bg/gps/angtype iso
/gate/source/bg/gps/mintheta 0. deg
/gate/source/bg/gps/maxtheta 180. deg
/gate/source/bg/gps/minphi 0. deg
/gate/source/bg/gps/maxphi 360. deg

This is the only source I have set in the macro.
Does anyone have any idea what the reason for this might be?
Thank you
Enrico