Gamma decay is one of the three radioactive decay modes available to atomic nuclei, along with alpha and beta decay. In alpha and beta decay, the atomic number of the nucleus changes, but in gamma decay the atomic number does not change. In gamma decay, a nucleus in an excited energy state decays to a lower-energy state by emitting a high-energy photon. The photons produced in this decay are consequently known as gamma rays and have a wavelength with an order of magnitude of about 1,000 femtometers, or 10-12 meters. The decay process is very similar to the absorption and emission of light by atoms in the ultraviolet, visible, and infrared spectrums.

Gamma decay often follows either alpha or beta decay in a decay process. Following an alpha or beta decay, the number of protons and neutrons in the nucleus has changed, and the resulting nucleus may...