Enhanced nuclear resonance scattering in dynamical diffraction of gamma rays

The angular and energy dependence of the dynamical diffraction of gamma rays was studied experimentally in the symmetric Bragg case. Mossbauer diffraction spectra were measured with high angular resolution in pure nuclear Bragg reflection of a nearly perfect 57 FeBO 3 single crystal. In the spectrum taken at the exact Bragg position, very broad hyperfine resonance peaks were observed. In the spectra just above and below the Bragg angle the reflection peaks were much smaller and were shifted to energy positions above and below resonance respectively. The results were interpreted by means of the dynamical theory and compared with computer calculations. The measurements represent the first direct observation of the enhancement of nuclear resonance scattering in the case of a thick crystal reflection. Furthermore the angular dependence of the resonance scattering by a perfect single crystal has been measured for the first time.