Local deviations from the Grodzins systematics for the product $E\left(2^{+}\right)B\left(E 2\right)$ are observed in several light Ra-Th nuclei. We note an abrupt increase to 5.5% of the isoscalar $E 2$ energy-weighted sum rule, almost a factor of 2 above the value typically found near shell closures and equal to the value found in the very deformed actinides. This indicates mixing of a low-lying deformed state into the ground state of the light Ra-Th nuclei, as expected for a low-lying cluster state. Evidence for mixing of a deformed state is also present in the rms radii and binding energies of these nuclei.

• Received 13 April 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.2424