[[Gamma ray|Gamma radiation]] given off "promptly" following a [[nuclear]] reaction: ie., fission, or by the interaction of a [[neutron]] and a stable nucleus. For example, a nucleus excited by capturing a neutron, or by the [[inelastic scattering]] of a very fast neutron. sheds excess energy by the emission of one or more prompt [[gamma ray|gamma-ray]] photons. See also [[delayed gamma ray]].