Structural evolution of octupole-deformed radium isotopes within a coupled-channels method

We have systematically investigated the spectroscopic properties in even-even Ra 222 − 228 by introducing the cluster degrees of freedom within the coupled-channels method, which allows the core Pb 208 to occupy the octupole 3 − state (Calc. I), as well as both the octupole 3 − and quadrupole 2 + states (Calc. II), along with multipole interactions. Excellent agreement has been achieved between our calculated results and available data on energy spectra, reduced electromagnetic E λ transition-matrix elements, and intrinsic electric dipole, quadrupole, and octupole Q λ moments, pointing to the existence of strong octupole correlations in this region. The description of parity-doublet bands and electromagnetic-transition properties in both calculations is consistent with each other and with experimental data, which confirms the reliability of the coupled-channels formalism based on the cluster-core configuration in heavy nuclei. The enhanced E 2 and E 3 matrix elements in both calculations for Ra 222 − 226 suggest that these three nuclei can exhibit static octupole deformation in both positive- and negative-parity bands. On the other hand, the accurate reproduction of the higher negative-parity bandhead and the derived Q 3 moments in nucleus Ra 228 is consistent with the interpretation of this nucleus as a deformed rotor exhibiting dynamic/soft octupole vibrations. We hope that the present work may open new avenues for exploring octupole collectivity and cluster correlations in heavy nuclei.