1. Spontaneous disintegration of a radionuclide with the emission of energetic particles or radiation, such as alpha or beta particles or gamma rays.
2. An instance of such disintegration.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.