What phenomenon is specifically caused by gamma rays?

Gamma rays are high-energy electromagnetic radiation produced by the decay of radioactive materials. Their interaction with matter is primarily characterized by their ability to ionize atoms and molecules. Ionization occurs when gamma rays transfer sufficient energy to electrons within an atom, thereby ejecting them from their orbits and creating ions.

This phenomenon is crucial in various fields, especially in radiation therapy, where ionization is leveraged to damage the DNA of cancer cells. Unlike chemical reactions, which involve the rearrangement of atoms in compounds, or thermal radiation, which involves the emission of energy as heat by matter, gamma rays specifically induce ionization without necessarily leading to a subsequent chemical transformation. Additionally, gamma rays do not play a direct role in molecular bonding, which is more closely associated with interactions between atoms when they share or exchange electrons. Therefore, the distinctive capability of gamma rays to ionize matter is what makes this option the correct choice.