I read that photons can interact with electrons, atoms or simply disintegrate. The four cases I came across are. 1. Compton scattering. 2. Photoelectric effect 3. Knock an electron to a higher energy state in an atom. 4. electron-positron pair production. While I understand each process what determines when one would occur as opposed to another. For example, under what conditions does Compton scattering occur vs. the photoelectric effect?