Observation of the high-resolution Mössbauer resonance in Ge73

The high-resolution Mössbauer effect of the 13.3-keV transition τ=4.3μsec) in Ge73 has been observed in transmission experiments at room temperature. The recoilless γ-ray source was carrier-free As73 diffused into a single crystal of elemental germanium; the absorber was a thin single-crystal layer of enriched Ge73 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 2Γ 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.