Most fissions are binary fissions (producing two charged fragments), but occasionally (2 to 4 times per 1000 events), three positively charged fragments are produced, in a ternary fission. The two (or more) nuclei produced are most often of comparable but slightly different sizes, typically with a mass ratio of products of about 3 to 2, for common fissile isotopes. Like nuclear fusion, for fission to produce energy, the total binding energy of the resulting elements must be greater than that of the starting element.įission is a form of nuclear transmutation because the resulting fragments (or daughter atoms) are not the same element as the original parent atom. In their second publication on nuclear fission in February 1939, Hahn and Strassmann predicted the existence and liberation of additional neutrons during the fission process, opening up the possibility of a nuclear chain reaction.įor heavy nuclides, it is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments ( heating the bulk material where fission takes place). Frisch named the process 'fission' by analogy with biological fission of living cells. Physicists Lise Meitner and her nephew Otto Robert Frisch explained it theoretically in January 1939. Nuclear fission was discovered on 19 December 1938 in Berlin by German chemists Otto Hahn and Fritz Strassmann. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radioactive decay. Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei.

Uranium 235 plus neutrino