[Gate-users] ion source less coincidences

[Pedro Correia]

Hello Gaters!

I’m facing a problem using a Na22 ion source in a PET scanner that I want to model.

My simulation consists only in two LYSO crystals, aligned, and two sources between them. When I use a gamma back-to-back source or a positron source, the number of coincidences that I get is, lets say, 1000.
When I use the ion source, the number of coincidences decreases to 400. I now that when using positron, one needs to consider the 100% efficiency of gamma conversion, that doesn’t happen with the ion source, but my experimetal setup, that is equal to the simulation. gives me very similar results with the ones obtained for gamma back-to-back and positron sources, but not when I use the ion source. 

Any ideia on why am I getting (much) less coincidences with the ion source?

Part of the code is bellow:

#Physics
/gate/physics/addPhysicsList emstandard_opt2
/gate/physics/addProcess            Decay
/gate/physics/addProcess            RadioactiveDecay
/gate/physics/addProcess            PositronAnnihilation

#Plastic phantom around the source
/gate/world/daughters/name              phantom
/gate/world/daughters/insert            cylinder
/gate/phantom/setMaterial               Plastic
/gate/phantom/vis/setColor              grey
/gate/phantom/geometry/setRmax          6.35 mm
/gate/phantom/geometry/setHeight        4 mm
/gate/phantom/placement/setTranslation  -6.35 0 0 mm

#Source
/gate/source/addSource                          na22
/gate/source/na22/setActivity                   5.26e-6 Ci
/gate/source/na22/gps/particle                  ion
/gate/source/na22/gps/ion                       11 22 0 0
/gate/source/na22/gps/monoenergy                0. keV
/gate/source/na22/gps/type                      Volume
/gate/source/na22/gps/shape                     Cylinder
/gate/source/na22/gps/radius                    1.55 mm #3.1 mm diameter
/gate/source/na22/gps/halfz                     1.125 mm  #2.25 mm z
/gate/source/na22/gps/angtype                   iso
#/gate/source/na22/gps/centre                   -6.35 0. 0. mm
/gate/source/na22/attachTo                      phantom
/gate/source/na22/setForcedUnstableFlag         true
/gate/source/na22/setForcedHalfLife             82048007.5 s


Thanks in advance.
Pedro