Physical Review Letters ( IF 8.385 ) Pub Date :
P. A. Butler et al.

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 ${}^{222,228}$Ra nuclei using the method of sub-barrier, multi-step 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 ${}^{222}$Ra as pear-shaped with stable octupole deformation, while ${}^{228}$Ra behaves like an octupole vibrator.

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