Radiation Safety Practice Exam

Which type of particle loses energy each time ionization occurs and cannot penetrate a sheet of paper?

1. Beta particle

2. Gamma ray

3. Alpha particle

4. Neutron

The correct answer is: Alpha particle

The correct answer is alpha particle because alpha particles are relatively large and carry a positive charge. When they encounter matter, they interact strongly with atoms, causing significant ionization along their path. This ionization leads to a loss of energy, causing alpha particles to slow down rapidly. Due to their size and charge, alpha particles have a very limited range and can be stopped by a sheet of paper or even the outer layer of human skin. In contrast, beta particles, which are smaller and lighter than alpha particles, can penetrate more deeply into materials but still have limited penetration compared to gamma rays. Gamma rays, being electromagnetic waves, have high penetration capabilities and can pass through several centimeters of lead. Neutrons are neutral particles and can also penetrate materials to a greater extent than alpha particles since they do not ionize materials directly through electric interactions, but rather through nuclear reactions. Thus, the unique characteristics of alpha particles make them the only type of particle listed that cannot penetrate a sheet of paper after losing energy through ionization.