Pair production
In physics, pair production can happen when a photon with a lot of energy is near the nucleus of an atom. This most commonly makes an electron and a positron. It can also make other subatomic particles, but it has to make the antiparticle (opposite particle) of that subatomic particle too. The two particles go in opposite directions.
Pair production is more common if the photon has a lot of energy. It is also more common if the nucleus has a bigger atomic number. Pair production usually happens with energy levels over 25 MeV. Pair production happens sometimes in radiation therapy treatments that use photon beams with a lot of energy. It is somewhat related to photoelectric effect.
Pair Production Media
Diagram showing the process of electron–positron pair production. In reality the produced pair are nearly collinear. The black dot labelled 'Z' represents an adjacent atom, with atomic number Z.
Plot of photon energies calculated for a given element (atomic number Z) at which the cross section value for the process on the right becomes larger than the cross section for the process on the left. For calcium (Z=20), Compton scattering starts to dominate at hυ=0.08 MeV and ceases at 12 MeV.
Subatomic particle pair production
Feynman diagram of electron–positron pair production. One must calculate multiple diagrams to get the net cross section
