"Compton effect"
Expected headings
"Annihilation"
"Applications"
"The reason at least 1.022 MeV of photon energy is necessary is because the resting mass (using E=MC² ) of the electron and positron expressed in units of energy is 0.511 MeV (or 9.1 x 10-31 kg) each, therefore unless there is at least 0.511 MeV *2 (i.e., 1.022 MeV) it is not possible for the electron-positron pair to be created. If the energy of the incident photon is greater than 1.022 MeV, the excess is shared (although not always equally) between the electron and positron as kinetic energy."
"PP is related to the atomic number (Z) of attenuator, incident photon energy (E) and physical density (p) by Z E (- 1.022) p."