Answer: Lead or concrete (dense material).
- A A sheet of paper, sufficient mainly for stopping alpha particles
- B A thin sheet of aluminum, sufficient mainly for stopping beta particles
- C Lead or concrete (dense material)
- D A thick layer of ordinary air at atmospheric pressure
Correct answer: C. Lead or concrete (dense material)
Explanation: Gamma rays are high-energy photons. Dense materials (lead, concrete) are effective shields. Alpha stopped by paper, beta by Al.
Binding energy per nucleon rises sharply for light nuclei, peaks around iron-56 (the most stable nucleus), then slowly declines for heavier nuclei - which is exactly why fusing light nuclei or splitting heavy nuclei both release energy: each moves the products toward this stability peak.
Concept context
Radioactivity, nuclear reactions, fission, fusion, and binding energy.