nuclear fission

American  

[noo-klee-er fish-uhn] / ˈnu kli ər ˈfɪʃ ən /

noun

1. fission.

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nuclear fission British  

noun

1. Sometimes shortened to: fission.  the splitting of an atomic nucleus into approximately equal parts, either spontaneously or as a result of the impact of a particle usually with an associated release of energy Compare nuclear fusion

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fission, nuclear Cultural  

1. A nuclear reaction in which a single large nucleus splits into two or more smaller nuclei. In some cases, for example with uranium, energy is released in this process.

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Pronunciation

See nuclear ( def. ).

Discover More

The fission of uranium 235, an isotope of uranium, supplies energy for nuclear reactors and atomic bombs (see also atomic bomb).

Etymology

Origin of nuclear fission

First recorded in 1885–90

Example Sentences

The fusion process creates energy by joining atoms together, while nuclear fission creates energy when atoms are split apart.

From The Wall Street Journal • Dec. 10, 2025

It is produced by nuclear fission for use in medical gauges and devices, but can also be a byproduct of nuclear reactors and weapons testing, the agency said.

From Los Angeles Times • Aug. 19, 2025

It will contain radioactive uranium split by nuclear fission, in a chain reaction which generates a lot of heat.

From BBC • Dec. 4, 2024

Sam Altman, who also chairs Oklo, a nuclear fission microreactor start-up that’s set to go public this year, is backing the power source to satisfy the world’s growing energy needs, including from A.I.

From New York Times • Mar. 21, 2024

The roots of the meeting had been planted more than two years earlier by the discovery of nuclear fission.

From "Big Science" by Michael Hiltzik