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nuclear chain reaction
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First self-sustaining nuclear chain reaction
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nuclear chain reaction

physics
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First self-sustaining nuclear chain reaction
First self-sustaining nuclear chain reaction Scientists observing the world's first self-sustaining nuclear chain reaction, in the Chicago Pile No. 1, December 2, 1942. Photograph of an original painting by Gary Sheehan, 1957.

A nuclear chain reaction is a process where neutrons released from the fission of one atomic nucleus initiate the fission of other nuclei. This self-sustaining sequence is fundamental to nuclear physics. For a chain reaction to occur, a minimum amount of fissile material, known as the critical mass, is required.12

The process involves several stages:
* Initiation: A neutron triggers the fission of a fissile nucleus.
* Propagation: The fission releases more neutrons, which then cause further fissions, creating a multiplying effect.1
* Termination: The reaction stops when there are no longer enough neutrons to sustain fission, or through other mechanisms.1

If the number of neutrons causing fission is exactly one per generation, the reaction is self-sustaining (critical), as seen in nuclear reactors. If more than one neutron per generation causes fission, the reaction accelerates rapidly, leading to a divergent chain reaction, as in nuclear explosions. This controlled release of energy is harnessed in nuclear reactors for electricity generation.34

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4 Britannica Sources
  1. critical mass
  2. chain reaction
  3. nuclear fission - Fission chain reactions and their control
  4. nuclear energy

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