I have a question I am working on for which I need some help. "Using E^2 - p^2c^2 = invariant, calculate the thresholds for pair production and triplet production." This is what I have for pair production: Pair Production E^2 – p^2c^2 = invariant therefore, E > pc, for each electron produced, where E is the photon energy hv E > 2[m0 v c (excess KE of electron) + m0 c^2 (rest mass of an electron)] = 2 m0 c^2 , since v = 0 for minimum photon energy E > (2)(9.1E-31 kg)(2.998E8 m/s)2 E > 1.636E-13 J / 1.602E-13 J/MeV E > 1.02 MeV I am stuck on the triplet production. I found one reference that has the KE transferred to the stationary electron with the excess photon momentum = me-c^2, m sub e- Any help or critique would be appreciated. Thanks.