Editing Chain reaction (section)

==Nuclear chain reactions==
{{main|Nuclear chain reaction}}
A ''nuclear'' chain reaction was proposed by [[Leo Szilard]] in 1933, shortly after the neutron was discovered, yet more than five years before [[nuclear fission]] was first discovered. Szilárd knew of ''chemical'' chain reactions, and he had been reading about an energy-producing [[nuclear reaction]] involving high-energy protons bombarding lithium, demonstrated by [[John Cockcroft]] and [[Ernest Walton]], in 1932. Now, Szilárd proposed to use neutrons theoretically produced from certain nuclear reactions in lighter isotopes, to induce further reactions in light isotopes that produced more neutrons. This would in theory produce a chain reaction at the level of the nucleus. He did not envision fission as one of these neutron-producing reactions, since this reaction was not known at the time. Experiments he proposed using [[beryllium]] and [[indium]] failed.

Later, after fission was discovered in 1938, Szilárd immediately realized the possibility of using neutron-induced fission as the particular nuclear reaction necessary to create a chain-reaction, so long as fission also produced neutrons. In 1939, with Enrico Fermi, Szilárd proved this neutron-multiplying reaction in uranium. In this reaction, a [[neutron]] plus a fissionable [[atom]] causes a fission resulting in a larger number of neutrons than the single one that was consumed in the initial reaction. Thus was born the practical [[nuclear chain reaction]] by the mechanism of neutron-induced nuclear fission.

Specifically, if one or more of the produced neutrons themselves interact with other fissionable nuclei, and these also undergo fission, then there is a possibility that the macroscopic overall fission reaction will not stop, but continue throughout the reaction material. This is then a self-propagating and thus self-sustaining chain reaction. This is the principle for [[nuclear reactor]]s and [[atomic bomb]]s.

Demonstration of a self-sustaining nuclear chain reaction was accomplished by [[Enrico Fermi]] and others, in the successful operation of [[Chicago Pile-1]], the first artificial nuclear reactor, in late 1942.