[Gate-users] point source and sensitivity

[Hongwei Ye]

Dear GATE users:


I'm trying to get the sensitivity image for a ECAT system using a series of  simulations of point sources. But I met some problems: for a point source (a sphere with 1000 Bq, 0.1~0.5 mm radius, back-to-back gammas in vacuum) at center, the coincidences increase with radius !!! This seems odd to me. Should #coincidences keep same (or almost same)? The following data is radius----#coincidences for scans with 1 second only:

            0.1---11; 0.2---106; 0.3---192; 0.4---247; 0.5---319

I copy a part of code here for your checking:

gate/source/addSource PointSource
/gate/source/PointSource/setActivity 1000 Bq

/gate/source/PointSource/gps/particle gamma
/gate/source/PointSource/setType backtoback
/gate/source/PointSource/setForcedUnstableFlag true
/gate/source/PointSource/setForcedHalfLife 6586 s
/gate/source/PointSource/gps/energytype Mono
/gate/source/PointSource/gps/monoenergy 511. keV


/gate/source/PointSource/gps/type Volume
/gate/source/PointSource/gps/shape Sphere
/gate/source/PointSource/gps/radius 0.4 mm
/gate/source/PointSource/gps/centre 0.0 0.0 0.0 cm

And #coincidences is too high (=0.319 for sensitivity) for this ECAT system when radius=0.5 mm. By some simple calculations, the sensitivity at center is about 0.18. Could anyone point me out what is wrong, or tell me how to do "point source" simulations?

Thanks a lot.

 Hongwei



      
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