1. The problem statement, all variables and given/known data Is it possible for pair production to occur without interacting mwith matter? 2. Relevant equations E+ + E- = E(gamma) - 2*m_e*c^2 3. The attempt at a solution In the Coulomb field of nucleus (or electron), the incident photon energy can be converted to the creation of an electron-positron pair. A minimum of 2*m_e*c^2 is required for this purpose. Each of the annihilation photons can then interact with the surrounding medium via the photoelectric effect or, more likely, Compton scattering. I've never been truly able to understand this question qualitatively. I keep imagining that the photon is not present but have always wondered how this would allow the interaction to occur physically? Can this be shown explicitly using conserved quantities for this interaction?