The first stage of scintillation, conversion, is the process where the energy from the incident radiation is absorbed by the scintillator and highly energetic electrons and holes are created in the material. The energy absorption mechanism by the scintillator depends on the type and energy of radiation involved. For highly energetic photons such as X-rays (0.1 keV < E γ γ < 100 keV) and γ-rays ( E γ γ > 100 keV), three types of interactions are responsible for the energy conversion process in scintillation: photoelectric absorption, Compton scattering, and pair production, which only occurs when E γ γ > 1022 keV, i.e. the photon has enough energy to create an electron-positron pair.