Gamma rays, high-energy photons or short-wavelength electromagnetic waves, are emitted from the nucleus along with an alpha or beta decay. When an alpha or beta decay produces a daughter nucleus that nucleus is often in an excited state. One or more gammas are emitted as the nucleus settles down to its lowest energy, or ground state. Gammas are like high-energy X rays, but are emitted from the nucleus, not the electrons, of an atom.