Which type of ionizing radiation can be stopped by a sheet of paper?

• A. Beta
• B. Gamma
• C. Alpha
• D. Neutron

Answer: (C)

The main idea here is how differently each type of ionizing radiation interacts with matter and how much shielding they need. Alpha radiation consists of heavy, positively charged helium nuclei. Their large size and charge cause them to lose energy very quickly as they pass through material, so they travel only a short distance and can be stopped by something as thin as a sheet of paper. That’s why a sheet of paper is enough to halt alpha particles.

Beta particles are smaller and more penetrating than alpha particles; they can be stopped by a few millimeters of plastic or aluminum, so paper isn’t reliably sufficient shielding for them. Gamma rays are photons with no mass or charge and are highly penetrating; they go through paper easily and require dense shielding like lead or concrete. Neutrons, depending on their energy, are slowed and captured by hydrogen-rich materials such as water or polyethylene, often with additional shielding as needed.

So alpha radiation is the type that can be stopped by a sheet of paper.