What does fission refer to in nuclear science?

Fission is a key concept in nuclear science that specifically describes a process where a large, unstable nucleus splits into two or more smaller nuclei, along with the release of energy. This splitting occurs when the nucleus absorbs a neutron, which destabilizes it and causes it to break apart. The resultant smaller nuclei are usually in a state of lower energy than the original nucleus, and this release of energy is what makes fission a powerful process, particularly in applications such as nuclear reactors and atomic bombs.

In contrast, the other options refer to different processes. Fusion, for example, involves the merging of small nuclei to form a larger nucleus, which is not what fission describes. Radioactive decay is a different phenomenon where unstable atomic nuclei lose energy by emitting radiation, but it does not involve splitting a nucleus. Lastly, chemical reactions involve the rearrangement of atoms and do not include nuclear processes, which are fundamentally different in nature from chemical reactions. Understanding fission is essential for comprehending the principles of nuclear energy and its applications.