Kernresonanzabsorption nicht Doppler-verbreiterter Gammastrahlung in Re187

Nuclear resonant absorption of gamma-rays has been observed in nuclei of Re¹⁸⁷ bound in a crystal lattice. At a temperature of 20° K a small fraction of the gammaquanta of the 134 keV transition to the ground state is emitted with essentially no energy lost to recoil, the recoil momentum being taken up by the entire crystal, not by the individual nucleus. Nuclei of Re¹⁸⁷ similarly bound in a crystal lattice have been irradiated with such gamma-rays emitted without loss of energy, resulting in an oberservable resonance absorption. Using a relative velocity of the order of 10 cm/sec the line emitted with the natural line width has been shifted away from the absorption line, resulting in the destruction of the resonance phenomena. Analysis of the variation in transmission as a function of the Doppler shift of the emitted gamma-ray yields a value ofτ=(1,5±0,2) · 10^?11 sec for the lifetime of the 134 keV excited state in Re¹⁸⁷.