Electron pairs simultaneously emitted from a solid surface upon excitation with photons (double photoemission or (γ,2e) ) or electrons (e,2e) provide information about the electron correlation in the solid which is mediated by exchange and Coulomb interactions. Without the Pauli restriction, the correlation of a positron with many electrons in a solid is dominated by Coulomb interactions. We have therefore undertaken the first comparative study of electron-electron and positron-electron pair emission upon impact with low energy photons, electrons and positrons. The target surface chosen for this study was LiF(100), a wide band gap dielectric that allows for a simple kinematical interpretation of the energy distribution of emitted pairs. We present the first results and discuss insights into the mechanisms of pair emission upon positron, electron and photon impact.