What is the best method of shielding against gamma radiation?

The best method of shielding against gamma radiation is lead. Gamma rays are highly penetrating electromagnetic radiation, which means they can pass through many materials with relative ease. To effectively shield against gamma radiation, a material must have a high atomic number and density, as these properties significantly enhance the material's ability to absorb or scatter gamma photons.

Lead is particularly effective due to its high density (approximately 11.34 g/cm³) and high atomic number (82). When gamma rays interact with lead, they are more likely to be absorbed or scattered, thus reducing the intensity of radiation that can penetrate through the shielding. This property allows lead to be used in various applications, such as radiation shielding in medical settings and nuclear facilities.

In contrast, plastic sheeting, wooden boards, and cardboard lack the necessary density and atomic number to provide effective shielding against gamma radiation. These materials may offer some protection against lower-energy radiation, like alpha and beta particles, but they are insufficient for gamma rays due to their ability to penetrate through these lighter materials easily.