Anomalousγ-Band Intraband Transition Rates inEr166

The 7+→6+, 6+→5+, and 5+→4+ intraband transitions within the $\gamma$ vibrational band of ${\mathrm{Er}}^{166}$ have been observed. The intensities of these transitions have been measured relative to the $E2\mathrm{}$ crossover transitions which originate from the same states. The $\Delta I=-1\mathrm{}$ "stopover" transitions have intensities which exceed the Alaga-rule predictions for pure $E2\mathrm{}$ $\Delta I=-1\mathrm{}$ transitions. The excess intensity is indicative of an $M1\mathrm{}$ admixture into these transitions, in contrast to a vanishing $M1\mathrm{}$ rate which would be anticipated if rotational states correspond to the rotation of a uniform nuclear fluid. The square of the $M1\mathrm{}$ matrix element, which is deduced from these data, increases with the spin of the initial state approximately as $I^2{\mathrm{}(I+1\mathrm{})\mathrm{}}^2$.