Nuclear Resonance Absorption of Gamma Rays at Low Temperatures

Recent experiments by Mossbauer have shown that nuclear resonance absorption of gamma rays can take place when both source and absorber are placed at liquid nitrogen temperature. The source used in his measurements was Os/sup 191/ which decays to Ir/sup 191/with a 16-day haif life. This beta decay populates a 4.9-sec isomeric state which cascades through the 129-kev excited state of this nucleus. The present experiment was designed to measure the lifetime of this excited state. (W.D.M.)