Fission (fissioning)

[Rennhack]

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.

[Rennhack]

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. Fissioning is also referred to as 'burning.' (See also fusion.) 

Fissioning that occurs without any outside cause, such as bombardment with a neutron, is called 'spontaneous fission.'