Which material is commonly used for shielding high-energy gamma radiation?

• A. Wood.
• B. Plastic.
• C. Concrete.
• D. Lead.

Answer: (D)

Shielding gamma radiation hinges on how easily the material can absorb or scatter photons, which comes down to its density and atomic number. High-energy gamma rays interact with matter mainly through scattering and pair production, and the likelihood of these interactions grows with the number of electrons per volume and with the atomic number. Materials with high density and high atomic number provide many opportunities for interaction and therefore attenuate gamma rays more effectively per unit thickness.

Lead has both a very high density and a high atomic number, so it presents a large number of electrons in a compact space. This makes it excellent at stopping or reducing gamma photons quickly as they pass through. Wood and plastic are light with low atomic numbers, so they offer little attenuation for high-energy gamma rays. Concrete is denser than wood or plastic and better than those materials, but its attenuation per centimeter is still usually lower than that of lead for high-energy gamma radiation. Therefore, lead is commonly used for shielding high-energy gamma rays because it provides the strongest attenuation in a relatively compact barrier.