Setup: A world volume box, Na 22 source
While using G4 air, I see position annihilation happening, the emission of two 180-degree photons. I am confused about whether this is realistic or if I need to change my material definition.
While using a vacuum-like material, I am not observing the positron annihilation.
Can someone please point out any inadequacies in the material and/or physics definitions that I am missing here ?
Think about the “reality” of what you’ve set up. Na-22 decays emitting a positron, right? If that positron hits material (G4_Air) with actual atoms, it should annihilate, giving you a couple of 511 keV gammas.
Your “Galactic” or “G4_Galactic” is defined with a density of 1e-25 g/cm3, or 0.06 atoms/cm3. That’s about 16 cm between atoms. How big is your box? 1 m? Then that positron might only encounter ~6 atoms or less before it leaves the world, so positron annihilation is quite unlikely.
