  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 $E$3 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.
