What is the process by which an unstable atomic nucleus loses energy?

The process by which an unstable atomic nucleus loses energy is known as radioactive decay. This occurs when an unstable nucleus seeks to reach a more stable state by emitting particles or electromagnetic radiation. During radioactive decay, the nucleus undergoes transformations that result in the release of energy, which may be in the form of alpha particles, beta particles, or gamma rays. This method of energy loss is essential in understanding nuclear stability and the various forms of radioactive isotopes.

Nuclear fusion and fission are processes involving the combination of nuclei or the splitting of a large nucleus, respectively, and while both release energy, they do not specifically describe the natural energy loss of unstable nuclei. Electromagnetic radiation, on the other hand, is a form of energy release that can occur as a result of radioactive decay but does not encompass the entire process of energy loss from an unstable nucleus. Thus, radioactive decay specifically defines the mechanism of energy loss in unstable atomic nuclei.