A method for producing stimulated emission of gamma radiation comprising: 1] providing at least first and second gamma-radiation sources, both sources being in recoil-free first-excited nuclear levels and the second source being in resonance with the first source and the gamma radiation from the first source being incident on the second source, 2] during the lifetime of its excited state, abruptly moving the first source through a distance equal to 1/2 the wavelength of the radiation emitted therefrom, thereby inducing a .pi.-phase-shift gamma radiation transparency in the second source whereby the .pi.-phase-shifted gamma radiation stimulates the excited nuclear resonant state of the second source to emit gamma radiation.