[Gate-users] (no subject)

[MELISSAS Maximilien (SAFRAN)]

Dear Gaters,

I am facing an issue I don't understand, with my current description of my setup, it seems that the X rays scattering depends on the order in which volumes have been declared



To mimic the CT scan of a composite material (I am using Gate to understand a CT-Scan setup used for Aeronautical part testing), I am introducing a periodic network of carbon fiber along each direction in my test phantom (Let’s call these direction 1, 2, 3)



If I check the branches ComptVolName and RayleighVolName in the Hit Tree, there is always one direction producing more scattering. However, whatever the rotation of the phantom, the later-declared direction is always the one producing the most scattered hits.

Here is a pseudo phantom.mac

/gate/world/daughters/name epoxyBox

#Define an epoxy box,

/gate/epoxyBox/daughters/name CCylinder1

#Define and rotate an array of carbon Cylinder using Repeater

/gate/epoxyBox/daughters/name CCylinder2

#Define and rotate an array of carbon Cylinder using Repeater

/gate/epoxyBox/daughters/name CCylinder3

#Define and rotate an array of carbon Cylinder using Repeater



All the Carbon cylinders are copy-pasted and I change only the rotation along X/Y/Z . After running the simulation, if I check which volumes produces the most scattered hits (from Hits/CompVolName and Hits/RayleighVolName) the volume producing the most scattered hits is CCylinder3 whatever the rotation of the epoxyBox

If now I declare the CCylinder in a different order i.e

/gate/epoxyBox/daughters/name CCylinder3

#Define and rotate an array of carbon Cylinder using Repeater

/gate/epoxyBox/daughters/name CCylinder1

#Define and rotate an array of carbon Cylinder using Repeater

/gate/epoxyBox/daughters/name CCylinder2

#Define and rotate an array of carbon Cylinder using Repeater

Now the CCylinder producing the most scattered hits is CCylinder 2 (whatever the rotation of the epoxy box)

I made all the rotation testing with few photons (around 100 000) to save Computing time, and I ran another orientation with 10 000 000 photons to be sure I am not seeing statistical fluctuations



Am I misunderstanding the meaning of the Rayleigh/ComptVolName (actually, how is this leaf filled when a photon has been scattered several times)?  Is it another feature that I don’t understand or am I facing a bug?



Cheers,

Maximilien



--

Maximilien MELISSAS

Consultant, Alten technology

Image processing for CT NDT @ Safran composite

http://www.alten.com


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