Which of the following are examples of ionizing particles?

• A. Gamma rays and X-rays
• B. Ultraviolet photons
• C. Energetic alpha particles, beta particles, and neutrons
• D. Infrared photons

Answer: (C)

Ionizing particles are those that can remove electrons from atoms as they pass through matter. Energetic alpha particles, beta particles, and neutrons fit this because each interacts with material in a way that produces ionizations. Alpha particles are heavy helium nuclei with a +2 charge, creating many ion pairs along a short path due to strong Coulomb interactions. Beta particles, fast electrons or positrons, ionize as they traverse matter by colliding with atoms and ejecting electrons. Neutrons, though uncharged, collide with atomic nuclei and transfer energy that yields recoil fragments or secondary charged particles, which then ionize surrounding atoms. In contrast, photons such as gamma rays and X-rays are electromagnetic radiation—they can ionize at high energies, but they are not material particles, while infrared photons do not have enough energy to ionize.