What is the process called when an atomic nucleus splits?

The process when an atomic nucleus splits is called fission. In fission, a heavy nucleus, such as that of uranium-235 or plutonium-239, absorbs a neutron and becomes unstable, resulting in the nucleus splitting into smaller nuclei, along with the release of energy, additional neutrons, and often gamma radiation. This reaction is significant because it underpins the operation of nuclear reactors and atomic bombs, showcasing its ability to produce a substantial amount of energy from a small amount of matter.

In contrast, fusion is the process where two light atomic nuclei combine to form a heavier nucleus, releasing energy in the process. Radioactivity refers to the spontaneous emission of particles or radiation from an unstable atomic nucleus, and decay is related to the transformation of a radioactive isotope into a different element or isotope over time. While these processes relate to the behavior of atomic nuclei, they are fundamentally different from fission, which specifically involves the splitting of a nucleus.