Deutsch: Spaltung / Español: Fisión / Português: Fissão / Français: Fission / Italiano: Fissione /

A fission is the process whereby the nucleus of a particular heavy Element splits into (generally) two nuclei of lighter elements, with the Release of substantial amounts of energy.

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Other /More definition:
A fission is the splitting of a nucleus into at least two other nuclei and the release of a relatively large amount of energy. Two or three neutrons are usually released during this type of transformation.