<P> Chemical chain reactions were first proposed by German chemist Max Bodenstein in 1913, and were reasonably well understood before nuclear chain reactions were proposed . It was understood that chemical chain reactions were responsible for exponentially increasing rates in reactions, such as produced in chemical explosions . </P> <P> The concept of a nuclear chain reaction was reportedly first hypothesized by Hungarian scientist Leó Szilárd on September 12, 1933 . 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 . </P> <P> In 1936, Szilárd attempted to create a chain reaction using beryllium and indium, but was unsuccessful . Nuclear fission was discovered and proved by Otto Hahn and Fritz Strassmann in December 1938 . A few months later, Frédéric Joliot, H. Von Halban and L. Kowarski in Paris searched for, and discovered, neutron multiplication in uranium, proving that a nuclear chain reaction by this mechanism was indeed possible . </P> <P> On May 4, 1939 Joliot, Halban et Kowarski filed three patents . The first two described power production from a nuclear chain reaction, the last one called "Perfectionnement aux charges explosives" was the first patent for the atomic bomb and is filed as patent n ° 445686 by the Caisse nationale de Recherche Scientifique . </P>

This is another name for the factor that might trigger an event