Definition of "nuclear reaction" []

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

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Eventually — or so the theory goes — one of these cycles will dump enough matter onto B to trigger a proton-proton nuclear reaction in the surface."