What does radioactive decay refer to?

Radioactive decay refers to the process by which a radioactive atom releases energy in the form of radiation as it transforms into a more stable state. This transformation often results in the emission of particles such as alpha or beta particles, or radiation such as gamma rays. The key aspect of this process is that it involves the unstable nuclei of radioactive atoms transitioning to a more stable configuration while shedding excess energy.

This process is fundamental to understanding radioactivity and the behavior of isotopes, since the energy released during decay can lead to both beneficial applications, such as in medical treatments and energy generation, as well as potential hazards if not properly managed.

In contrast, the other choices reflect different concepts not directly linked to the definition of radioactive decay. For instance, stable atoms do not become unstable through decay; they maintain their integrity unless acted upon by external forces or interactions. Ionization and activation refer to different processes involving interactions with radiation or particles, rather than the intrinsic decay characteristic of radioactive materials.