Federal Emergency Management Agency (FEMA) Standardized Awareness Practice Test

Which of the following radioactive emissions has the least penetrating power?

1. Gamma rays

2. Beta particles

3. Alpha particles

4. Neutrons

The correct answer is: Alpha particles

Alpha particles have the least penetrating power compared to other types of radioactive emissions. This is due to their larger mass and positive charge, which means they interact more strongly with matter. As a result, alpha particles can be stopped by a sheet of paper or even the outer layer of human skin. In contrast, gamma rays are highly penetrating electromagnetic waves that can pass through most materials, including human tissue, making them much more difficult to shield against. Beta particles, which are electrons or positrons, have better penetrating ability than alpha particles but are still less penetrating than gamma rays. Neutrons, while also relatively penetrating, require materials such as water or plastic for effective shielding due to their lack of charge and subsequent interaction with atomic nuclei. Understanding the penetration power of these emissions is crucial for radiation protection and safety measures, indicating that alpha particles represent the least threat in terms of penetration ability.