Which shielding material is most commonly used for X-ray and gamma shielding, and why does thickness matter?

• A. Concrete, because it's cheap and dense; thickness does not matter.
• B. Lead, due to high atomic number and density; thickness reduces transmission (HVL concept).
• C. Wood, because it's easy to work with; thickness is irrelevant.
• D. Aluminum, due to light weight; thickness increases scatter.

Answer: (B)