Pair production is a direct conversion of radiant energy into matter in accordance witht he equation E = m c ², where E is the amount of energy, m is the mass, and c is the speed of light.  It is one of the prinicpal ways in which high-energy gamma rays are absorbed in matter.  The positrons quickly disappear by being reconverted into photons in the process of Annihilation with other electrons!  Pair production may sometimes be refered to the formation of other particle/antiparticle pairs also!