Nuclear chain reaction

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A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating number of these reactions. The specific nuclear reaction may be the fission of heavy isotopes (e.g. 235U) or the fusion of light isotopes (e.g. 2H and 3H). The nuclear chain reaction is unique since it releases several million times more energy per reaction than any chemical reaction.

Contents

History

Chemical chain reactions were first proposed by German chemist Max Bodenstein in 1913, and reasonably well understood before nuclear chain reactions were proposed. [1] 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 August 12, 1933. The neutron had been discovered in 1932, shortly before. Szilard realized that if a nuclear reaction produced neutrons, which then caused further nuclear reactions, the process might be self-perpetuating. Szilard, however, did not propose fission as the mechanism for his chain reaction, since the fission reaction was not yet discovered or even suspected. Instead, Szilard 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.[2]

In 1936, Szilárd attempted to create a chain reaction using beryllium and indium, but was unsuccessful. After nuclear fission was discovered by others in 1938, 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.[3] This discovery prompted the letter from Albert Einstein to President Franklin D. Roosevelt warning of the possibility that Nazi Germany might be attempting to build an atomic bomb.[4]

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