Comparison of stopping and attenuation powers (defined as the inverse of the massic absorption and attenuation coefficients) as a function of the gamma energy. Attenuation and absorption powers are rather close to each other when the photoelectric effect dominates. Lead is a very effective energy absorber up to 200 MeV, because of the dominance of the photoelectric effect for heavy nuclei. In the case of a light absorber such as water, the Compton effect dominates: the stopping power is much weaker. The vairation with energy is less marked.