American Society of Radiologic Technologist (ASRT) Practice Exam

In terms of radiation exposure, which type of radiation is most biologically damaging?

1. Gamma rays

2. Beta particles

3. Alpha particles

4. X-rays

The correct answer is: Alpha particles

Alpha particles are considered the most biologically damaging type of radiation due to their high mass and charge. When alpha particles, which consist of two protons and two neutrons, interact with biological tissues, they have a significant ability to ionize atoms and molecules. This ionization process can cause substantial damage to cellular structures, including DNA, which may result in mutations, cancer, or cell death. The high linear energy transfer (LET) of alpha particles means that they deposit energy in a very short range, making them highly effective at causing localized damage within living tissues. While alpha particles are not able to penetrate skin or external barriers, if ingested or inhaled, they can inflict serious internal damage due to their strong ionizing capabilities. In comparison, gamma rays, beta particles, and X-rays have lower mass and charge, which typically leads to less ionization per unit distance traveled in biological tissues. Gamma rays and X-rays, while highly penetrating, have lower LET than alpha particles, thus causing less biological damage on a per interaction basis. Beta particles, being lighter than alpha particles, also have a lower potential for causing significant damage when compared to the robust damage inflicted by alpha radiation.