(physics) a process that alters the energy or structure or composition of atomic nuclei WordNet 3.0 & Open English WordNet

In nuclear physics and nuclear chemistry, a nuclear reaction is a process in which two nuclei, or a nucleus and an external subatomic particle, collide to produce one or more new nuclides. Wikipedia

Process in which two nuclei collide to produce one or more nuclides Wikidata

A reaction involving a change in an atomic nucleus, such as fission, fusion, neutron capture, or radioactive decay, as distinct from a chemical reaction, which is limited to changes in the electron structure surrounding the nucleus. OmegaWiki

A process such as the fission of an atomic nucleus, or the fusion of one or more atomic nuclei and/or subatomic particles in which the number of protons and/or neutrons in a nucleus changes; the reaction products may contain a different element or a different isotope of the same element. Wiktionary

Process. Wiktionary (translation)