[Gate-users] Optical tracking problem in Gate6.0p01

[Esteban Venialgo]

Hi all,


I'm simulating a LYSO pixel of 5x5x25.4 mm3 attached to a huge light 
guide of 260x260x10 mm3. And the light guide is coupled to a big 
photocathode of 260x260x0.5 mm3.

I'm studying the light spread of the LYSO pixel, for this reason the 
light guide is pretty huge. To study this, I need to analyze the 
gatehits file and check the position of the light photons when they 
reach the detection surface which is between the photocathode and the 
light guide.


These are the geometrical definitions of my simple detector:


# Defino el pixel de LYSO
/gate/SPECThead/daughters/name pixel
/gate/SPECThead/daughters/insert box
/gate/pixel/geometry/setXLength 5 mm
/gate/pixel/geometry/setYLength 5 mm
/gate/pixel/geometry/setZLength 25.4 mm
/gate/pixel/placement/setTranslation 0 0 5 mm
/gate/pixel/setMaterial LYSO
/gate/pixel/vis/forceSolid
/gate/pixel/vis/setColor yellow


# Defino el lightGuide
/gate/SPECThead/daughters/name lightGuide
/gate/SPECThead/daughters/insert box
/gate/lightGuide/geometry/setXLength 260 mm
/gate/lightGuide/geometry/setYLength 260 mm
/gate/lightGuide/geometry/setZLength 10 mm
/gate/lightGuide/placement/setTranslation 0 0 -12.7 mm
/gate/lightGuide/setMaterial Plastic
/gate/lightGuide/vis/setColor blue
/gate/lightGuide/vis/forceSolid


# Defino el fotocatodo gigante
/gate/SPECThead/daughters/name superFotocatodo
/gate/SPECThead/daughters/insert box
/gate/superFotocatodo/geometry/setXLength 260 mm
/gate/superFotocatodo/geometry/setYLength 260 mm
/gate/superFotocatodo/geometry/setZLength 0.5 mm
/gate/superFotocatodo/placement/setTranslation 0 0 -17.95 mm
/gate/superFotocatodo/setMaterial Plastic
/gate/superFotocatodo/vis/setColor red
/gate/superFotocatodo/vis/forceSolid




The problem is that with Gate6.0p01 the simulation doesn't seem to be 
working, and with Gate3.1.2 it is working.

I've made the histograms of X,Y and Z positions of the transported light 
photons of the gateHits file for both cases, gate6.0p01 and gate3.1.2, 
and there is a big difference.

I've attached these histograms and the openGL windows for both 
simulations. And as you can see in the histograms, the position of the 
transported light photons is correct in the case of Gate3.1.2 because 
the Z position corresponds with the interface between the light guide 
and the photocatode; however, the Z position of the transported photons 
of Gate6.0p01 corresponds with the surface between the LYSO pixel and 
the lightguide. Furthermore, the X and Y positions of the light photons 
simulated with gate6.0p01 are limited to the pixel area without any spread.

To conclude, it seems that Gate6.0p01 is storing the coordinates of the 
light photons when they are transported from the pixel to the light 
guide, instead of storing the coordinates when they are transported from 
the light guide to the photocatode.


P.S.: Also, I've attached a piece of the gateHit files for both versions 
of Gate.


                                                            Esteban 
Venialgo.



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