What will protect you from gamma rays?

• A. steel or lead shielding
• B. wood shielding
• C. plastic shielding
• D. water shielding

Answer: (A)

Gamma rays are highly penetrating, so protection comes from dense, high atomic-number materials that can efficiently absorb or scatter photons. Dense metals with high Z increase the chances of gamma-ray interactions (photoelectric absorption and Compton scattering), and thus reduce the beam’s intensity quickly. Lead is the classic choice because its high density and high atomic number give strong attenuation, so a relatively thin layer can significantly shield you. Steel also provides good shielding, though you typically need a bit more thickness than lead to achieve the same protection. In contrast, wood and plastic are low-density, low-Z materials and little gamma shielding is achieved per inch. Water can provide some attenuation, but it’s not as effective as lead or steel for the same thickness. So the best protection from gamma rays comes from steel or lead shielding.