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.