|Message: Re: Positron annihilation coordinates||Not Logged In (login)|
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Ok, so the 'feature' in your histogram is real. You should be curious as to why some events do not have an e+ annihilation. You can do this by writing out the random number at the start of one of those events and you then re-launch the event with that seed with step-wise debugging set on. If you don't know how to do this, there should be ample instructions in the G4 documentation/forum/FAQ etc.
> I even tried to use GetVertexPosition instead of GetPosition but I > always get (0,0,0). Shouldn't it actually give me the position of the > vertex where the track was originated?
It could well be that the vertex position is not yet filled for the track in StackingAction. It should certainly be filled as you expect in SteppingAction. Have a look.
In any event, it looks to me now that your 'feature' has a physical explanation and there is one for the missing entries as well. The only other possibility for it is the logic with which you arrive in your code to fill the histogram.