Simulating 3-photon annihilations

My group is currently attempting to simulate 3-photon annihilations to mimic that of ortho-Positronium self annihilation decay.

We have concluded that fully simulating o-Ps formation and then its annihilation is perhaps too complicated. Instead we want to simply simulate the 3-photon kinematics after annihilation. However, we are having trouble figuring out how to properly and randomly select the momentum vectors and energy of each photon such that the net momentum is 0 and the net energy sums to 1022 keV.

Could someone point us to a physics model that does this well or perhaps a clever method that we could implement ourselves with particle generator such that the 3 gammas meet the specifications I mentioned above?

We have tried to use the G4eplusTo3GammaOKCModel() and while this does allow for 3-photon annihilations, the result is not what we want, neither momentum or energy seems to be conserved. We also ensured to set annihilations to occur at rest, yet this model still allowed for 3-photon decays that had a net momentum. This may be because this model was intended for a specific purpose, not o-Ps self annihilations.

Thank you, I am happy to provide any additional information!


we still in process to establish 3 gamma annihilation simulation. The model class G4eplusTo3GammaOKCModel is created not to be a separate model but as an alternative to G4eplusTo2GammaOKCModel. The reason - Geant4 electromagnetic physics design assumed that for given energy only 1 model is active. So, this model should have a mechanism to choose 2 gamma or 3 gamma should be produced for a given positron. Currently it is work in progress.


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