Isomer shifts of the $2^{+}$ → $0^{+}$ rotational transition in ${}_{}{}^{154}{}_{}{}^{}\mathrm{Gd}$ were determined in Mössbauer measurements. From comparison with isomer shifts in ${}_{}{}^{156}{}_{}{}^{}\mathrm{Gd}$ and ${}_{}{}^{158}{}_{}{}^{}\mathrm{Gd}$, the ratios $\frac{\Delta {〈r^2〉}_{154}}{\Delta {〈r^2〉}_{156}}=+7.3\mathrm{}\pm 1.9$ and $\frac{\Delta {〈r^2〉}_{154}}{\Delta {〈r^2〉}_{158}}=+30\mathrm{}\pm 10$ are deduced. These ratios imply a considerable increase in rigidity for deformed nuclei above neutron number $N=90\mathrm{}$. The existing theoretical values are discussed.

• Received 10 March 1969

DOI:https://doi.org/10.1103/PhysRevLett.22.790