Overview
Nuclear fission is a process where the nucleus of a heavy atom—such as uranium-235 or plutonium-239—splits into two or more smaller nuclei, accompanied by the release of free neutrons, gamma photons, and a significant amount of energy. This reaction is exothermic, meaning it releases more energy than it consumes, and is governed by Einstein’s mass-energy equivalence principle (E=mc²). The energy released stems from the conversion of a tiny fraction of the nucleus’s mass into energy. Fission is distinct from nuclear fusion, which combines nuclei, and from radioactive decay, which involves spontaneous particle emission.Fission reactions are harnessed in nuclear power plants to generate electricity and in nuclear weapons for explosive energy. The process requires a critical mass of fissile material to sustain a chain reaction, where released neutrons trigger further fissions. Uncontrolled chain reactions power atomic bombs, while controlled reactions in reactors are moderated to produce steady energy output.
History/Background
The discovery of nuclear fission emerged in 1938–1939 through experiments by German chemists Otto Hahn and Fritz Strassmann, with theoretical interpretation by Lise Meitner and Otto Frisch. They observed that bombarding uranium with neutrons produced barium, indicating the uranium nucleus had split. This breakthrough laid the groundwork for the Manhattan Project (1942–1945), the U.S.-led effort to develop atomic bombs during World War II.The first controlled nuclear chain reaction was achieved on December 2, 1942, by Enrico Fermi’s team at the University of Chicago’s Chicago Pile-1 reactor. Post-war, nuclear fission transitioned to peaceful uses: the world’s first nuclear power plant, Obninsk in the Soviet Union, began operation in 1954. The 1970s saw rapid global adoption of nuclear energy, though accidents like Chernobyl (1986) and Fukushima (2011) highlighted safety challenges.
