Nuclear chain reaction

A sequence of nuclear reactions in which products of one reaction trigger further reactions. Depending on the conditions, the sequence can die out, sustain itself, or grow rapidly.

Neutron multiplication factor: The ratio of neutrons in one generation to those in the preceding generation in a multiplying nuclear system. Its value distinguishes a fading, steady, or growing chain reaction.
Neutron: An electrically neutral subatomic particle found in atomic nuclei and emitted in some nuclear reactions. Neutrons are the main carriers of the chain from one fission event to another.
Nuclear reactor: A device that maintains a controlled nuclear fission chain reaction to produce heat or useful radiation. Reactors hold the chain near a steady rate to generate usable energy.
Leo Szilard: A Hungarian-American physicist who conceived the nuclear chain reaction and helped develop the first nuclear reactor. His 1933 insight framed the possibility of neutron-driven nuclear multiplication.
Neutron moderation: The slowing of neutrons through scattering, commonly by nuclei in a surrounding material. Slower neutrons can make fission more likely in some reactor fuels.
Uranium-235: A fissile isotope of uranium whose nucleus can split after absorbing a neutron. It is a common fuel capable of sustaining a fission chain reaction.
Nuclear weapon: A weapon that releases energy through nuclear fission, fusion, or both. Fission weapons use rapidly multiplying chain reactions for explosive energy release.
Enrico Fermi: An Italian-American physicist who led the team that achieved the first controlled, self-sustaining nuclear chain reaction. His experiments culminated in the first reactor demonstration.
Neutron capture: A nuclear reaction in which an atomic nucleus absorbs a neutron. Capture removes neutrons from the chain unless it leads to another fission.
Fissile material: Material containing nuclides that can undergo fission after absorbing low-energy neutrons. This broader class identifies fuels that can support a chain under suitable conditions.

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