What is the splitting of an atomic nucleus into smaller parts called?

1. The nucleus at the centre of an atom is held together by very strong forces. 2. Breaking a nucleus apart releases a large amount of energy, and this is fission. 3. Joining two nuclei into one is the opposite process, called fusion. 4. Uranium is one of the substances used as a fuel for fission. _Source: Siyavula Natural Sciences Grade 7 (CC BY 4.0), Nuclear fuels_