|Message: Neutrons with ParticleGun along X axis instead of Z axis||Not Logged In (login)|
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I have a problem that shows that sending particles along the Z axis or X (or Y) axis does not lead to the same intrinsic physics properties.
I send neutrons of 100keV along the Z axis on a box filled with a gas. I track fluor recoils resulting from elastic collisions with neutrons. I get the angular distribution of these recoils regarding the Z axis. This angular distribution is OK.
Then, I send the neutrons on a perpendicular axis : along the X axis. I plot the angular distribution of the fluor recoils regarding the X axis (or the Z axis). This distribution is different from the previous one, which is physically inconsistent.
I use Geant4 version 10.01.p02, with the physics list QGSP_BERT_HP_LIV.
I changed the energy, the physics list, the gas nature to track other recoils, the geometry, and I tried different methods to get the angle of the recoil. The problem is always there : When neutrons are sent along the Z axis, the angular distribution of recoils is correct. When the neutrons are sent along the X or Y axis, the angular distribution is not correct, and always points to 0 degree.
The only way I found to overcome this difficulty was to rotate my geometry, and always send the particles along the Z axis...
Question : any idea of the cause ?
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