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Key Issues Nuclear Weapons The Basics What is Nuclear Fission?

What is Nuclear Fission?

The process whereby the nucleus of a particular heavy element splits into (generally) two nuclei of lighter elements, with the release of substantial amounts of energy. (Atomic Archive Glossary)

Fission was discovered in 1934 when Enrico Fermi of Italy irradiated uranium with neutrons and believed he had produced the first transuranic element. In 1938 Otto Hahn and Fritz Strassmann of Germany split the uranium atom by bombarding it with neutrons and showed that the elements barium and krypton were formed. Fermi, Hahn and Strassmann did, however, not realize that they had in fact induced a fission reaction. Only later research by others established the necessary knowledge about the nuclear fission process.

During the process of nuclear fission a particle such as a neutron strikes the nucleus of a

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uranium atom and causes it to split into two fragments. Each of the two fragments consists of a nucleus with roughly half the neutrons and protons of the original nucleus. This fission process releases a large amount of energy in the form of warmth and radiation. Gamma rays are emitted as well as two or more neutrons that are no longer bound by the fission fragments. These so-called "free" neutrons are now capable of splitting other uranium nuclei, which then release neutrons that split still more nuclei. A series of such nuclear fissions is called a "chain reaction," which is accompanied by an enormous release of nuclear energy. In a controlled process, chain reactions can be harnessed to produce electrical energy in a nuclear power plant. The devastating destruction that is caused by the explosion of atomic bombs results from an uncontrolled chain reaction.