Monochromatization of synchrotron radiation down to about ${10}^{\mathrm{-}8}$ eV at an energy of 14.4 keV has been achieved by double nuclear Bragg diffraction from ${}_{}{}^{57}{}_{}{}^{}\mathrm{yttrium}$ iron garnet single-crystal films set for the electronically forbidden {200} reflection. The monochromatized γ quanta have been analyzed with respect to time delay and capabiltiy of resonance absorption. By setting of appropriate energy and time windows a pure beam of resonant γ quanta at a rate of about 1 Hz is available.

• Received 26 December 1984

DOI:https://doi.org/10.1103/PhysRevLett.54.835