nuclear reaction

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A reaction, as in fission, fusion, or radioactive decay, that alters the energy, composition, or structure of an atomic nucleus.

from the GNU version of the Collaborative International Dictionary of English.

• noun A process that alters the energy or structure or composition of an atomic nucleus.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun 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

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (physics) a process that alters the energy or structure or composition of atomic nuclei