Time-Differential—Perturbed-Angular-Correlation Measurement of the Hyperfine Field at Hg in Iron

The hyperfine magnetic field at Hg nuclei in iron has been measured using the method of time-differential perturbed angular correlations on the 158-keV state of ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$. The parent activity of ${}_{}{}^{199}{}_{}{}^{}\mathrm{Tl}$ was implanted into pure-iron foils employing an isotope separator. The results are consistent with about 80% of the nuclei experiencing a hyperfine field of $\left|H_{\mathrm{int}}\right|=670\mathrm{}\pm 65$ kG and the remainder a field of $\left|H_{\mathrm{int}}^{\prime }\right|=455\mathrm{}\pm 85$ kG. These results, combined with previous lattice-location studies of Tl in Fe, indicate that the high field corresponds to the impurity atoms at substitutional sites. Using the value of $H_{\mathrm{int}}$ for the substitional sites derived here, the $g$ factors of the first excited $2^{+}$ states of the even-even nuclei ${}_{}{}^{198-204}{}_{}{}^{}\mathrm{Hg}$, obtained from previously reported experiments, have been recomputed.