Hyperfine Magnetic Field atHg198in Iron

The precession of the 412-keV state ($\tau =31.9\mathrm{}\pm 3.2 \mathrm{psec},g=0.55\mathrm{}\pm 0.11$) of ${}_{}{}^{198}{}_{}{}^{}\mathrm{Hg}$ in the internal field in iron was measured by observing the integral magnetically perturbed angular correlation (IMPAC) of the 675-412-keV cascade. Several sources differing in metallurgical treatment and in the way the parent activity of ${}_{}{}^{198}{}_{}{}^{}\mathrm{Au}$ was introduced into the Fe were measured. Ion-implanted sources yielded the same hf field as carefully annealed metallurgical sources ($H_0=640\mathrm{}\pm 160 \mathrm{kOe},\omega \tau =54\mathrm{}\pm 6 \mathrm{mrad}$), whereas unannealed or rapidly quenched sources yielded lower values for the hf field ($H_{}^{\prime }{}_0{}^{}=520\mathrm{}\pm 130 \mathrm{kOe},{\omega }_0\tau =44\mathrm{}\pm 5 \mathrm{mrad}$). The low-field values may be associated with the ${}_{}{}^{198}{}_{}{}^{}\mathrm{Au}$ impurity atoms trapped in imperfections in the Fe crystal. Using the high value for $H_0$ determined in the present work together with previous IMPAC results on Coulomb-excited ${}_{}{}^{198}{}_{}{}^{}\mathrm{Hg}$ nuclei implanted into iron, a value for the transient magnetic effect on Hg nuclei recoiling through iron is calculated and is in agreement with the known transient-field systematics.