What can stop gamma rays?

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

Answer: (A)

Gamma rays are highly penetrating and require dense shielding to attenuate them. Shielding effectiveness increases with material density and atomic number, so thicker, denser materials reduce gamma-ray intensity more effectively per unit thickness. Among the given options, concrete provides the best shielding because it is dense and can be used in substantial thickness, making it more effective at reducing gamma rays than wood, plastic, or ice. Remember that attenuation depends on both the material and how thick the barrier is, so a sufficiently thick concrete barrier is needed to noticeably reduce gamma radiation.