[Gate-users] Concentric sources

[G. Delso]

Hi all,

I'm trying to simulate two overlapping, concentric spherical sources, the inner one with twice the activity of the outer one. I would expect this to have an additive effect, yielding an interior region with three times more counts than the exterior.
However, my simulations always end up with an interior region with only twice the counts of the exterior. Checking the output Root file confirms that both sources have behaved as if they had roughly the same activity concentration.

Can somebody explain this?

Kind regards

Gaspar Delso

-------------------------------------------------------------------------
/gate/source/addSource F18SphereSource
/gate/source/F18SphereSource/setActivity 1005000. becquerel
/gate/source/F18SphereSource/setType backtoback
/gate/source/F18SphereSource/gps/particle gamma
/gate/source/F18SphereSource/gps/confine NULL
/gate/source/F18SphereSource/gps/angtype iso
/gate/source/F18SphereSource/gps/mintheta 0. deg
/gate/source/F18SphereSource/gps/maxtheta 180. deg
/gate/source/F18SphereSource/gps/minphi 0. deg
/gate/source/F18SphereSource/gps/maxphi 360. deg
/gate/source/F18SphereSource/gps/energytype Mono
/gate/source/F18SphereSource/gps/monoenergy 511. keV
/gate/source/F18SphereSource/gps/type Volume
/gate/source/F18SphereSource/gps/shape Sphere
/gate/source/F18SphereSource/gps/radius 20. mm
/gate/source/F18SphereSource/gps/centre 5.2 -5.9 0. cm

/gate/source/addSource F18SphereSource2
/gate/source/F18SphereSource2/setActivity 251000. becquerel
/gate/source/F18SphereSource2/setType backtoback
/gate/source/F18SphereSource2/gps/particle gamma
/gate/source/F18SphereSource2/gps/confine NULL
/gate/source/F18SphereSource2/gps/angtype iso
/gate/source/F18SphereSource2/gps/mintheta 0. deg
/gate/source/F18SphereSource2/gps/maxtheta 180. deg
/gate/source/F18SphereSource2/gps/minphi 0. deg
/gate/source/F18SphereSource2/gps/maxphi 360. deg
/gate/source/F18SphereSource2/gps/energytype Mono
/gate/source/F18SphereSource2/gps/monoenergy 511. keV
/gate/source/F18SphereSource2/gps/type Volume
/gate/source/F18SphereSource2/gps/shape Sphere
/gate/source/F18SphereSource2/gps/radius 10. mm
/gate/source/F18SphereSource2/gps/centre 5.2 -5.9 0. cm

/gate/source/list
-------------------------------------------------------------------------------
Source --------------> F18SphereSource
  ID                 : 0
  type               : backtoback
  activity (Bq)      : 1.005e+06
  startTime (s)      : 0
  time (s)           : 0
  forcedUnstable     : false
  forcedHalfLife (s) : -0.693147
  verboseLevel       : 0
---------------------- 

Source --------------> F18SphereSource2
  ID                 : 1
  type               : backtoback
  activity (Bq)      : 251000
  startTime (s)      : 0
  time (s)           : 0
  forcedUnstable     : false
  forcedHalfLife (s) : -0.693147
  verboseLevel       : 0
---------------------- 
------------------------------------------------------------------------------------


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