Which of the following materials is most commonly used to shield against gamma radiation?

Lead is the material most commonly used to shield against gamma radiation due to its high density and atomic number. Gamma rays are highly penetrating electromagnetic radiation, and effective shielding requires materials that can effectively absorb or attenuate this energy. Lead's density allows it to provide significant attenuation of gamma radiation through several mechanisms, including photoelectric absorption, Compton scattering, and pair production.

Unlike lighter materials such as wood, plastic, and glass, which are less effective against gamma radiation, lead offers superior protection at a relatively thinner thickness. For this reason, lead is extensively used in various applications, including radiation safety equipment, medical facilities, and industrial radiography, when high levels of gamma radiation are present.

The effectiveness of lead in stopping gamma rays is a critical factor in radiation safety practices, ensuring that exposure to harmful radiation is minimized for workers and the public.