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A nuclear chain reaction occurs when one single nuclear reaction causes an average of one or more subsequent nuclear reactions, thus leading to the possibility of a self-propagating series of these reactions. The specific nuclear reaction may be the fission of heavy isotopes (e.g. 235U). The nuclear chain reaction releases several million times more energy per reaction than any chemical reaction. ==History== Chemical chain reactions were first proposed by German chemist Max Bodenstein in 1913, and were reasonably well understood before nuclear chain reactions were proposed.〔(See this 1956 Nobel lecture for history of the chain reaction in chemistry )〕 It was understood that chemical chain reactions were responsible for exponentially increasing rates in reactions, such as produced chemical explosions. The concept of a nuclear chain reaction was first hypothesized by Hungarian scientist Leó Szilárd on Tuesday, September 12, 1933.〔http://netlibrary.net/articles/Le%C3%B3_Szil%C3%A1rd〕 The neutron had been discovered in 1932, shortly before. Szilárd realized that if a nuclear reaction produced neutrons, which then caused further nuclear reactions, the process might be self-perpetuating. Szilárd, however, did not propose fission as the mechanism for his chain reaction, since the fission reaction was not yet discovered or even suspected. Instead, Szilárd proposed using mixtures of lighter known isotopes which produced neutrons in copious amounts. He filed a patent for his idea of a simple nuclear reactor the following year.〔L. Szilárd, "Improvements in or relating to the transmutation of chemical elements," British patent number: GB630726 (filed: 28 June 1934; published: 30 March 1936). (esp@cenet document view )〕 In 1936, Szilárd attempted to create a chain reaction using beryllium and indium, but was unsuccessful. After nuclear fission was discovered and proved by Otto Hahn and Fritz Strassmann in December 1938,〔Lise Meitner: ''Otto Hahn - the discoverer of nuclear fission.'' In: Forscher und Wissenschaftler im heutigen Europa. Stalling Verlag, Oldenburg/Hamburg 1955.〕 Szilárd and Enrico Fermi in 1939 searched for, and discovered, neutron multiplication in uranium, proving that a nuclear chain reaction by this mechanism was indeed possible.〔H. L. Anderson, E. Fermi, and Leo Szilárd, "Neutron production and absorption in uranium," ''The Physical Review'', vol. 56, pages 284–286 (1 August 1939). Available on-line at (FDRlibrary.marist.edu )〕 This discovery prompted the letter from Szilárd and signed by Albert Einstein to President Franklin D. Roosevelt warning of the possibility that Nazi Germany might be attempting to build an atomic bomb.〔(AIP.org )〕〔(Atomicarchive.com )〕 Enrico Fermi and Leo Szilárd created the first artificial self-sustaining nuclear chain reaction, called Chicago Pile-1 (CP-1), in a racquets court below the bleachers of Stagg Field at the University of Chicago on December 2, 1942. Fermi's experiments at the University of Chicago were part of Arthur H. Compton's Metallurgical Laboratory, part of the Manhattan Project; the lab was later moved outside Chicago, renamed Argonne National Laboratory, and tasked with conducting research in harnessing fission for nuclear energy.〔 〕 In 1956, Paul Kuroda of the University of Arkansas postulated that a natural fission reactor may have once existed. Since nuclear chain reactions only require natural materials (such as water and uranium), it is possible to have these chain reactions occur where there is the right combination of materials within the Earth's crust. Kuroda's prediction was verified with the discovery of evidence of natural self-sustaining nuclear chain reactions in the past at Oklo in Gabon, Africa in September 1972.〔(Oklo: Natural Nuclear Reactors—Fact Sheet )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nuclear chain reaction」の詳細全文を読む スポンサード リンク
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