I was looking at the wiki article on electron-positron pair production (http://en.wikipedia.org/wiki/Pair_production) and have a question.
The article states that the photon energy needs to exceed the rest energy of the electron + positron (1.022 MeV). However, a photon at this threshold would produce particles with very little kinetic energy, meaning that they cannot be created very closely in order to escape each other. So, is there anyone that know how close together the particles are produced (as function of photon energy?)
I'm thinking of these particles as essentially point-like and with initial separation that is small compared to the photon-nucleus distance at pair creation. But that might be wrong.. I see that what I worry about goes away if the initial pair separation is of the order of fm, right?
