Nuclear fission is a type of nuclear reaction in which the nucleus of an atom splits into two (or sometimes more) smaller nuclei. This type of reaction releases energy, and is the basis for the energy production in nuclear reactors, as well as the destructive power of nuclear weapons.
Nuclear fission reactions typically involve several different types of particles, including neutrons, protons, and electrons. In the simplest type of nuclear fission reactions, called binary reactions, two nuclei of different elements react to form a single nucleus of a different element, as well as a few neutrons. For example, when a uranium-235 nucleus is bombarded by neutrons, it splits into two lighter nuclei, typically barium-141 and krypton-96, with three neutrons emitted in the process. The mass of the final nucleus is less than the initial nucleus, and the difference in mass is released as energy in the form of gamma rays and kinetic energy of the new nuclei.
Nuclear fission reactions can also be induced artificially, by bombarding certain isotopes with neutron particles. This can occur in several ways, including through the use of a linear accelerator to propel the neutrons, or through a nuclear reactor to breed more fissile material. Once induced, the reaction can sustain itself as long as the nuclei remain in an appropriate temperature range, as the new nuclei can act as neutron sources, thereby activating more fission reactions.
When two of the same type of nucleus react, the reaction is called a symmetric fission. Symmetric fission usually releases only energy, rather than new nuclei. When two different types of nuclei react, the reaction is called an asymmetric fission. Asymmetric fission produces multiple particles, including neutrons and new nuclei.
When a fission reaction is sustained, it produces nuclear chain reactions, as the neutrons released by the reaction can cause additional fission reactions in turn. If enough additional fission reactions occur, it can result in an uncontrolled chain reaction, which can result in what is known as a nuclear explosion. Nuclear power plants rely on controlled chain reactions, as they use the energy released by the reaction to produce electricity.
Nuclear fission reactions are the basis for current nuclear technology, and understanding the reactions is crucial for anyone interested in energy production and risk assessment in nuclear reactors. The reactions can also be used to create elements that do not exist naturally; these man-made elements are referred to as transuranic elements.
