Which of the following has the highest ability to cause biological damage?

Alpha particles have the highest ability to cause biological damage due to their unique physical properties. These particles are composed of two protons and two neutrons, making them relatively large and positively charged. When alpha particles interact with matter, they have a high mass and charge, which enables them to transfer energy more effectively to surrounding atoms. This results in more ionization events per unit distance traveled.

Additionally, alpha particles have a very short range in biological tissues; they can be stopped by a sheet of paper or the outer layer of skin. However, if alpha-emitting materials are ingested or inhaled, their localized energy deposition can cause significant cellular damage, increasing the risk of cancers and other health effects.

In contrast, gamma rays, which are high-energy electromagnetic radiation, and X-rays are less ionizing than alpha particles and can penetrate tissues more deeply without necessarily causing additional damage per interaction. Beta particles, while more ionizing than gamma and X-ray radiation, do not typically cause as much biological damage as alpha particles because they are lighter and less charged.

Thus, alpha particles' greater ionization potential and efficiency at causing biological damage make them the most damaging radiation type among the listed options.