Recoilless Resonance Absorption and Hyperfine Structure of the 6.2-keV State inTa181

A strong recoilless resonance absorption was observed for the 6.2-keV level ($T_{\frac{1}{2}}=6.8\mathrm{}$ μsec) of ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$. Using sources of ${}_{}{}^{181}{}_{}{}^{}\mathrm{W}$ in W-metal and Ta-metal absorbers, a line-width of 11 times the natural width was obtained, with isomer shifts in the range between 0.83 and 0.94 mm/sec, depending on the quality of the sources. From the hyperfine splitting in a longitudinal magnetic field the magnetic moment of the 6.2-keV level was determined to be ${\mu }_1=+(5.14\mathrm{}\pm 0.15){\mu }_N$.