Hyperfine anomaly in thezP726level of the4f6s76pconfiguration of europium I

The hyperfine interaction constants of the $z{}_{}{}^6{}_{}{}^{}P_{\frac{7}{2}}^{}{}_{}{}^{}$ and $z{}_{}{}^8{}_{}{}^{}P_{\frac{7}{2}}^{}{}_{}{}^{}$ levels of the configuration $4f{}_{}{}^7{}_{}{}^{}6s6p$ of the isotopes ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$ and ${}_{}{}^{153}{}_{}{}^{}\mathrm{Eu}$ have been remeasured with the laser-atomic-beam technique. The analysis yields values of -6.80(26)% and -1.00(3)%, respectively, for the hyperfine anomalies. The anomaly in the $z{}_{}{}^6{}_{}{}^{}P_{\frac{7}{2}}^{}{}_{}{}^{}$ level is the largest so far observed and deviates considerably from the ground-state hyperfine anomaly. The experimental values of the hyperfine anomaly are compared with a calculation based on Nilsson-type nuclear wave functions. Possibly the electronic-state dependence of the hyperfine anomaly is due to core polarization.