Competition between the Compton and photoelectric effects
Two main processes of gamma interaction with matter compete in the energy range of radioactivity gamma of (from a few keV to 1 or 2 MeV). As can be seen on the examples of carbon and lead, the outcome of the competition depends on the gamma energy, the electron density andatomic nucleus electric charge Z. The interaction probabilities for photoelectric effect are far higher from those of the Compton effect in the low energy range. Compton Effect becomes dominant for energies above 600 keV for lead and only 20 keV for carbon.
IN2P3 (Source Particle Data Group)