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Question a problem solved but why?? 

Forum: Geometry
Date: 20 Aug, 2012
From: <rr>

Hi,

I just started to use GEANT4 and I had a problem that I have solved now, but i don't understand why!!! My detector is a sequence of sensitive planes. My source is a proton and to shoot it i use a G4ParticleGun object. The initial position of my particle is set in the constructor of my PrimaryGeneratorAction class. The particle is shot on Z axis perpendicular to my sensors. Of course it was a mistake but i set the Z position of particle out of world. Until today i have always shot just one particle per time, and I never had problem. Otherwise when I try to shoot two particles (or more) per time, it seems that just one of them crosses all sensors. When the "/tracking/verbose" option is switched on, I realize that REALLY one particle crosses my sensors. The initial position as well as the final position is the same for ALL particles but it seems that just one of them is "seen" by my sensors. In addition if the visualization mode is on, I can see that the initial Z position is ok for one particle (OUT of world) while the others particles start IN the world BUT AFTER my sensors (then they aren't detected). At the end I realized that the initial Z position was out of world and I set it correctly and all works now but I don't understand why! Why, if i shoot just one particle i can set the initial position out of world and if i shoot more particles i can't do it? Why if i have just one sensor but severals particles and the initial position is out of world all works? (This also happens!!!!!)

Thank you in advance

R.

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