What provides the best protection from x-ray photons?

• A. Lead
• B. Glass
• C. Plastic
• D. Water

Answer: (A)

Attenuation of X-ray photons rises with the material’s atomic number and density because higher-Z atoms have more electrons and denser matter presents more material for interactions to occur. In diagnostic radiology, lead’s very high atomic number (Z = 82) and its substantial density mean X-ray photons are more likely to interact and be absorbed or scattered as they pass through it. This makes lead far more effective at blocking X-rays per unit thickness than other common materials, so it offers the strongest protection for shields, aprons, and barrier walls.

Glass, plastic, and water are much lower in atomic number and/or density, so they absorb far fewer photons for the same thickness. They can provide some shielding, especially if used in thick enough layers, but they don’t match lead’s attenuation capability.