Calculation of the angle in pair production

2018-06-05 08:21:29

Related to Angle in pair production, how can I calculate what is the angle in which two photons are emitted in pair production? I found that the angle should be 0.8 MeV/E but I do not have any idea where this number is coming from...

Would that also apply to the calculation of the angle of two photons emitted in a $\pi^0$ decay?