What material is most effective at absorbing gamma radiation?

Lead is the most effective material for absorbing gamma radiation due to its high density and atomic number. Gamma rays are a form of electromagnetic radiation, and they have a strong penetrating ability, which means they can pass through many materials. However, dense materials with high atomic numbers are more effective because they provide a greater likelihood of interaction with the gamma photons, thereby reducing their intensity.

Lead specifically absorbs gamma radiation by means of interactions such as photoelectric absorption, Compton scattering, and pair production. The thickness needed for effective shielding depends on the energy of the gamma rays being considered; however, even a few centimeters of lead can significantly decrease the radiation intensity.

Other materials listed are generally less effective for the purpose of gamma radiation shielding. For example, while several kilometers of air can attenuate gamma rays to some extent, this is not practical for shielding purposes, as it requires an impractically large distance. Stainless steel and concrete, although more effective than air, do not provide the same level of attenuation as lead in a compact form. Thus, lead is chosen for its efficiency and practicality in many gamma radiation shielding applications.