Pair Production

     Pair production of an elementary particle and its antiparticle, usually from a photon (or another neutral boson). 

    Provided there is enough energy available to create the pair - at least the total rest mass energy of the two particles - and that the situation allows both energy and momentum to be conserved.

    Energy from gamma rays is observed in condensed matter. Photon need only have a total energy of twice the rest mass of an electron (1.022 MeV) for this to occur. If it is much more energic, heavier particles may also be produced. 

    These interaction were first observed in Patrick Blackett's counter controlled bubble chamber, leading to the 1948 Noble Prize.