Which statement best describes lead's shielding effectiveness?

• A. Its high atomic number
• B. Its magnetic susceptibility
• C. Its low density
• D. Its thermal conductivity

Answer: (B)

Shielding effectiveness for X-rays comes from how likely photons are to interact with the material as they pass through. Lead’s high atomic number increases the probability of interactions like photoelectric absorption and scattering, especially at diagnostic X-ray energies. Its high density adds more material per unit thickness, so photons encounter more interactions even in a small layer. Magnetic susceptibility, on the other hand, describes how a material responds to magnetic fields and has little to do with X-ray attenuation. A lower density would reduce shielding, and thermal conductivity affects heat transfer, not photon attenuation.