Radiation Safety Practice Exam

Which particle has the least penetrating power but creates a significant number of ions?

1. Alpha particles

2. Beta particles

3. Gamma rays

4. X-rays

The correct answer is: Alpha particles

Alpha particles have the least penetrating power among the listed options, primarily due to their relatively large mass and positive charge. They consist of two protons and two neutrons, making them significantly heavier and larger than beta particles, gamma rays, and X-rays. This size and charge result in a high ionization density, meaning that as they travel through matter, they interact strongly with atoms along their path, leading to the creation of many ions. Although alpha particles can only travel a short distance—typically just a few centimeters in air and can be stopped by a sheet of paper—they can cause considerable damage to biological tissues if ingested or inhaled because of their strong ionizing capability. This ability to produce a significant number of ions is a crucial factor when considering the biological effects of radiation, underscoring why alpha particles are notable despite their low penetration ability. Beta particles, gamma rays, and X-rays, while having higher penetrating power, do not produce ions as densely as alpha particles do, due to their different mechanisms of interaction with matter.