The high-resolution Mössbauer effect of the 13.3-keV transition $\tau =4.3\mathrm{}$μsec) in ${}_{}{}^{73}{}_{}{}^{}\mathrm{Ge}$ has been observed in transmission experiments at room temperature. The recoilless $\gamma$-ray source was carrier-free ${}_{}{}^{73}{}_{}{}^{}\mathrm{As}$ diffused into a single crystal of elemental germanium; the absorber was a thin single-crystal layer of enriched ${}_{}{}^{73}{}_{}{}^{}\mathrm{Ge}$ epitaxially grown on a silicon substrate. The resonance absorption line, recorded with an electromechanical velocity spectrometer, has a corrected depth of ∼ 2.0%, and a (full width at half-maximum) linewidth $2\Gamma$ of 47(7) μm/sec, which is ∼ 7 times the natural linewidth. Despite the broadening this is the narrowest Mössbauer resonance observed so far at room temperature.

• Received 14 January 1974

DOI:https://doi.org/10.1103/PhysRevLett.32.512