Octupole correlations in the transitional actinides and the spdf interacting boson model

The region of light actinides (Z~88,N~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 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 (J12) in some of these nuclei (e.g., ²²⁶Ra) suggest that octupole deformation develops with increasing spin. We also discuss how octupole deformation can arise in the rotational (dynamical symmetry) limit.