The 122-14-keV $\gamma -\gamma$ cascade in ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ has been used to detect the precession of the 14-keV state in the hyperfine field produced by a Ni lattice at ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ impurity sites. The time-differential perturbed angular-correlation technique was used. The data yield a hyperfine field of -267.5±2.7 kG at room temperature. The magnitude is in agreement with Mössbauer measurements; the sign is determined here for the first time. The data also yield a half-life of 99.3±0.5 nsec for the 14-keV state, and an anisotropy coefficient $A_2=-0.0187\mathrm{}\pm 0.0015$ for the 122-14-keV cascade. In addition, the data show the absence of time-dependent perturbations over the experimental time interval of 400 nsec. Based on this, application to the study of critical field fluctuations is discussed.

• Received 20 March 1969

DOI:https://doi.org/10.1103/PhysRev.184.298