Observation of Centrifugal Stretching inSm152

An isomer shift has been observed in the Mössbauer study of the 121.8-keV ($2^{+}$→$0^{+}$) transition in ${\mathrm{Sm}}^{152}$. A value of ${\left(\frac{\Delta 〈R^2〉}{〈R^2〉}\right)}_{2-0}=(10\mathrm{}\pm 3)\times {10}^{-4\mathrm{}}$ is deduced, based on isotope shift data for ${\mathrm{Sm}}^{152}$ and ${\mathrm{Sm}}^{154}$. This value disagrees with present theoretical prediction. In particular, the influence of the $\beta$ band in ${\mathrm{Sm}}^{152}$ can only account for about 20% of the observed stretching.