Search for Parity Admixture in the 57.5-keV Gamma Transition ofHf180m

The possible explanation of the anomalous $L$-conversion coefficients of the 57.5-keV $K$-forbidden transition of ${\mathrm{Hf}}^{180m}$ as due to a parity mixture ($E1+M1\mathrm{}$) would imply a circular polarization of the $\gamma$ rays of 56%. By measuring the transmission of the radiation through a magnetized foil of Supermendur, a circular polarization of (5.9±6.1)% was obtained. We conclude that the anomaly found for the conversion coefficients is probably due to penetration effects.