What describes the process where unstable nuclei lose energy by emitting radiation?

The process where unstable nuclei lose energy by emitting radiation is known as radioactive decay. During this process, an unstable atomic nucleus transforms into a more stable configuration by releasing particles or electromagnetic radiation. This can involve the emission of alpha particles, beta particles, or gamma rays, each of which corresponds to different forms of radiation. The goal of radioactive decay is to achieve a balance in the number of protons and neutrons within the nucleus, ultimately leading to stability.

In contrast, nuclear fission refers to the splitting of a heavy nucleus into lighter nuclei, accompanied by the release of a significant amount of energy, but it is not simply about the emission of radiation for stability. Nuclear fusion involves the joining of lighter nuclei to form a heavier nucleus, also releasing energy but under different conditions, like those found in stars. A chain reaction occurs when the products of a nuclear reaction instigate further reactions, particularly in the context of fission, but does not directly describe the process of energy loss through radiation emission. Thus, radioactive decay is the correct term that encapsulates the loss of energy via radiation from unstable nuclei.