Absorption of gamma rays
Gamma rays deposit their energy inside a screen in many ways. In (A), a photon interacts by photoelectric effect: the electron is stopped almost right away. There is total absorption. In (B), the photon passes through the screen without interacting. In (C) the photon interacts through Compton effect: The Compton electron energy is absorbed locally, however the photon escapes. In the two last cases, there is total absorption because the photons are absorbed later on in the screen in D' and E''. The absorbed energy is the difference between incoming energy and outgoing energy.