[Gate-users] results problem

[mario bachaalany]

hi all,
I'm trying to simulate a pet system with four detectors made of LYSO 
crystals, a fluorine-18 as a source, and a sphere of water as a phantom, 
and I'm getting some kind of two peaks in the positron annihilation 
distance histogram in the root output. In general it must be a 
'decreasing  exponential function'. i already tried to change the 
geometry and  material of the phantom but still getting the same 
results. Does  anyone have the same problem and what could be the 
cause.......

thanks in advance.

Mario