The region of light actinides $(Z\sim 88,N\sim 134),$ which is thought to exhibit signs of stable octupole deformation, offers a real challenge for nuclear structure models. We study the even-even Ra-Th nuclei in the framework of the $\mathrm{spdf}$ interacting boson model and we find that while the properties of the low-lying states can be understood without stable octupole deformation, higher spin states $\left(J\gtrsim 12ħ\right)$ in some of these nuclei (e.g., ${}^{226}\mathrm{Ra})$ suggest that octupole deformation develops with increasing spin. We also discuss how octupole deformation can arise in the rotational (dynamical symmetry) limit.

• Received 7 December 2000

DOI:https://doi.org/10.1103/PhysRevC.63.054306