What type of particles can be stopped by a piece of paper?

• A. Beta
• B. Gamma
• C. Alpha
• D. X-ray

Answer: (C)

The correct choice relates to alpha particles, which are helium nuclei consisting of two protons and two neutrons. Due to their relatively large mass and charge, alpha particles have limited penetrating power. When encountering a barrier, such as a piece of paper, they can be effectively stopped because they lose energy quickly when interacting with matter. This means that even a thin sheet of paper is sufficient to prevent alpha particles from passing through.

In contrast, beta particles are smaller, high-energy electrons that can penetrate paper but are stopped by materials like plastic or glass. Gamma rays and X-rays have much higher energy, allowing them to penetrate most materials, including paper, and require denser substances such as lead or concrete for effective shielding. Understanding these characteristics helps in enforcing appropriate safety measures when dealing with different types of radiation.