What is Nuclear fission?
[[File:Nuclear fission.svg|250px|thumb|Nuclear fission diagram shows a [[neutron]] being absorbed by a [[uranium]] nucleus which then becomes unstable and splits into two new [[atom]]s with release of energy and some more neutrons.]] '''Nuclear fission''' is a kind of [[nuclear reaction]]. It is when an [[atom]] splits apart into smaller atoms. Some fission reactions give off a lot of energy, and are used in [[nuclear weapon]]s and [[nuclear reactor]]s. Nuclear fission was discovered in December 1938 by physicists [[Lise Meitner]] and [[Otto Frisch]], who observed a [[uranium]] [[Atomic nucleus|nucleus]] splitting in two. Although they originally thought the two tiny resulting nuclei were [[barium]] [[Isotope|isotopes]], what Meitner and Frisch truly saw was a process that would revolutionize nuclear chemistry: nuclear fission.<ref>{{Cite web|title=December 1938: Lise Meitner & Otto Frisch discover nuclear fission|url=http://www.aps.org/publications/apsnews/200712/physicshistory.cfm|access-date=2023-04-07|website=www.aps.org|language=en}}</ref> An atom is the smallest particle which makes up a [[chemical element]] (e.g. [[hydrogen]], [[oxygen]], [[magnesium]]). All atoms are very small. Atoms are made of three components or particles: [[Proton|Protons]], [[Neutron|neutrons]] and [[Electron|electrons.]] The protons and neutrons are clumped together in a ball called a [[nucleus (physics)|nucleus]], at the center of every atom. The electrons orbit around the nucleus in its '[[electron cloud]]'. Elements which have large nuclei, such as [[uranium]] and [[plutonium]], can be made to fission. If a (relatively) very large [[atomic nucleus]] is hit by a slow-moving neutron, it will sometimes become [[unstable]] and break into two nuclei. When the nucleus breaks apart (or '''fissions''') it releases energy, mostly as [[gamma ray]]s and heat. It also causes some neutrons to be released from the nucleus. For a few [[isotope]]s (an atom with the same amount of protons but a different amount of neutrons) such fission ca