Which radiation type could be stopped by a sheet of paper?

• A. Alpha particle
• B. Gamma ray
• C. Beta particle
• D. Cosmic ray

Answer: (A)

Penetration depends on the type of radiation and its energy. Alpha particles are heavy, doubly charged helium nuclei that interact strongly with matter and lose energy quickly, so they travel only short distances. A sheet of paper is enough to stop them because they deposit their energy over a very short path. In contrast, gamma rays are high-energy photons that pass through matter with little attenuation and require dense, thick shielding to reduce. Beta particles are faster electrons and are more penetrating than alpha particles but can be stopped by lightweight shielding like plastic or a thin metal—paper alone wouldn’t reliably stop higher-energy betas. Cosmic rays are extremely energetic particles from space and need substantial shielding, far beyond a sheet of paper, to slow them much. So the radiation type that can be stopped by a sheet of paper is the alpha particle.