Understanding Neutron Radiography Post Exam Reading VIII-Part 2a of 2A

Pair production (PP), like the photoelectric effect, results in the
complete attenuation of the incident photon. Pair production can only occur if
the incident photon energy is at least 1.022 MeV. As the photon interacts with
the strong electric field around the nucleus it undergoes a change of state and
is transformed into two particles (essentially creating matter from energy):
■ one electron
■ one positron (antimatter equivalent of the electron)
These two particles form the pair referred to in the name of the process. It is
noteworthy that other 'pairs' of leptons (of which the electron is a type) can be
created such as muon - antimuon and tau - antitau pairs, however the type of
lepton pair would dictate the energy of the incident photon necessary to
create them as both have far higher resting energy masses (1776 MeV for the
tau and 105 MeV for the muon) than the electron and positron.
Charlie Chong/ Fion Zhang
http://radiopaedia.org/articles/pair-production