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How does a nuclear fission chain reaction continue?
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actinoid element
Modern version of the periodic table of the elements (printable).
A nuclear fission chain reaction continues through the release of neutrons during the nuclear fission of heavy atomic nuclei, such as those of actinoid elements. When a nucleus splits, it emits several neutrons; if at least one of these neutrons successfully induces fission in another fissile nucleus, the process repeats, creating a self-sustaining series of events.123
The sustainability of this reaction is determined by the multiplication factor, k, which represents the ratio of fissions in one generation to the preceding one:1
- If k < 1: The reaction cannot be sustained.1
- If k = 1: A steady-state chain reaction is maintained, as seen in controlled nuclear reactors.13
- If k > 1: The number of fissions increases at each step, resulting in a divergent chain reaction, which is the principle behind atomic bombs.13
To maintain or control this process, reactors may use moderators to slow neutrons and movable control rods to absorb excess neutrons, ensuring the reaction remains stable.1