Hi, I am slightly confused regarding the termenology elastic and inelastic. My focus is on the interactions, Rayleigh, photoelectric, comptonscattering and pair production. I have read around the internet and have some question I did not fully got answered. 1) Is Elastic = Coherent and Ineleastic = Inchoherent? 2) Elastic is a process where the kinetic energy is conserved? This confuses me when one is dealing with photons because they have no mass so a kinetic energy is non existant? 3) Inelastic, neither the momentum nor the kinetic energy is preserved? 4) Inelastic is usually a process that needs a threshold energy? So if the above is true, then; Rayleigh and Thomson scattering is the only coherent/elastic scattering, and photoelectric + compton + pairproduction are incoherent/inelastic scattering? Thank you!