Discovery of nuclear fission.
Nuclear fission was discovered in December 1938 by physicists Lise Meitner and Otto Frisch, and chemists Otto Hahn and Fritz Strassmann. Fission is a nuclear reaction and process of radioactive decay in which the nucleus of an atom splits into two or more smaller, lighter nuclei. The fission process releases a very large amount of energy. The discovery that a nuclear chain reaction was possible led to the development of nuclear power and nuclear weapons. Hahn and Strassmann bombarded uranium with slow neutrons, and discovered that barium had been produced (illustration pictured). Meitner and her nephew Frisch theorised, and then proved, that the uranium nucleus had been split, and published their findings in Nature. Meitner calculated that the energy released by each disintegration was approximately 200 megaelectronvolts, and Frisch observed this. By analogy with the division of biological cells, Frisch named the process "fission". Hahn was awarded the 1944 Nobel Prize in Chemistry for the discovery.
