Experimentally realized linewidths of narrow (10eV) nuclear gamma resonances

The experimental status of Mössbauer linewidths are reviewed and reported for the three narrowest gamma resonances: ⁷³Ge, ⁶⁷Zn, and ¹⁸¹Ta. The crucial role played by the solid-state host in achieving narrow emission or absorption linewidths, as well as high recoil-free fraction are emphasized. Factors contributing to line-broadening in experiments with ¹⁸¹Ta and ⁶⁷Zn gamma resonances are highlighted. Consequences of these observations on a choice of a suitable lasing medium for Mössbauer gamma-ray lasers is commented upon.