[Gate-users] Potential bug in ring repeaters in GATE

[Zhengzhi Liu]

Dear GATE developers and users,

I recently came across a weird situation in GATE and have spent a few days
on it, but still could not figure it out why. Here is the problem:

In benchPET
<https://github.com/OpenGATE/Gate/blob/develop/benchmarks/benchPET/camera.mac>
and
GateContrib
<https://github.com/OpenGATE/GateContrib/blob/master/imaging/PET/PET_CylindricalPET_System.mac>,
the original code works fine, but soon as I change the times in the ring
repeater to 2 in the following code, there will be no coincidence event
recorded:

/gate/head/repeaters/insert                          ring
/gate/head/ring/setRepeatNumber               4

I did check all the details and nothing seems to have been changed
fundamentally, except that there are fewer detectors in the transaxial
plane. Even so, there are still two detector panels facing each other as
shown in the attached figure (benchPET_ring_repeaters_2.png). Each detector
panel has registered many singles as shown in the root plot
(hits_on_detectors.png). However, there was no coincidence event
registered, not event a single coincidence event. Originally I thought it
might be due to low geometrical sensitivity but after moving these detector
panels closer to each other and increasing simulation time, there was still
no coincidence event registered.

This phenomenon happens in both PET simulation cases mentioned above and
other PET simulations. Has anyone come across this problem before? Is this
a bug or simply my mistake?  Please give me any thoughts or help.

Thank you very much,
Sincere regards.

Zhengzhi
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