Fission

 **Fission** is a splitting of something into two parts. **Fission** may refer to:
 * In physics, [|nuclear fission] is a process where a large atomic nucleus (such as uranium) is split into two smaller particles.
 * In biology, [|fission (biology)] is the subdivision of a cell or a multi-cellular body into one or more parts and the regeneration of each of the parts into a complete individual.
 * In anthropology, fission is the process whereby a nation-state divides and becomes multiple states

F issile isotopes are isotopes of an element that can be split through fission. Only certain isotopes of certain elements are fissile. For example, one isotope of uranium, 235 U, is fissile, while another isotope, 238 U, is not. Other examples of fissile elements are 239 Pu and 232 Th. An important factor affecting whether or not an atom will fission is the speed at which the bombarding neutron is moving. If the neutron is highly energetic (and thus moving very quickly), it can cause fission in some elements that a slower neutron would not. For example, thorium 232 requires a very fast neutron to induce fission. However, uranium 235 needs slower neutrons. If a neutron is too fast, it will pass right through a 235 U atom without affecting it at all.