Evolution of octupole deformation in radium nuclei from Coulomb excitation of radioactive ²²²Ra and ²²⁸Ra beams

There is sparse direct experimental evidence that atomic nuclei can exhibit stable “pear” shapes arising from strong octupole correlations. In order to investigate the nature of octupole collectivity in radium isotopes, electric octupole (E3) matrix elements have been determined for transitions in ^222,228Ra nuclei using the method of sub-barrier, multistep Coulomb excitation. Beams of the radioactive radium isotopes were provided by the HIE-ISOLDE facility at CERN. The observed pattern of E3 matrix elements for different nuclear transitions is explained by describing ²²²Ra as pear shaped with stable octupole deformation, while ²²⁸Ra behaves like an octupole vibrator.