Hi maire,
If I understand correctly from the output, in this case the simulated positron annihilates with zero momentum, therefore at rest, not in-flight, and the two produced gammas have not 511-keV energy, as I would expect.
I’m a bit puzzled by this: if the positron annihilates at rest, the two gammas should be emitted back-to-back and with 511 keV each, right?
What I would like to simulate is positrons annihilating in-flight, when it is the case, therefore the gammas should be emitted slightly non-collinear (in that case).