The neutron-rich nucleus 144 Ba (t 1/2 =11.5 s) is expected to exhibit some of the strongest octupole correlations among nuclei with mass numbers A less than 200. Until now, indirect evidence for such strong correlations has been inferred from observations such as enhanced E1 transitions and interleaving positive-and negative-parity levels in the ground-state band. In this experiment, the octupole strength was measured directly by sub-barrier, multi-step Coulomb excitation of a postaccelerated 650-MeV 144 Ba beam on a 1.0-mg/cm 2 208 Pb target. The measured value of the matrix element, 3 − 1 M(E3) 0 + 1 = 0.65( +17 −23 ) eb 3/2 , corresponds to a reduced B(E3) transition probability of 48( +25 −34 ) W.u. This result represents an unambiguous determination of the octupole collectivity, is larger than any available theoretical prediction, and is consistent with octupole deformation.

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Despite the more than one order of magnitude difference between the measured dipole moments in 144 Ba and 146 Ba, the strength of the octupole correlations in 146 Ba are found to be as strong as those in 144 Ba with a similarly large value of B(E3; 3 − → 0 + ) determined as 48( +21 −29 ) W.u. The new results not only establish unambiguously the presence of a region of octupole deformation centered on these neutron-rich Ba isotopes, but also manifest the dependence of the electric dipole moments on the occupancy of different neutron orbitals in nuclei with enhanced octupole strength, as revealed by fully microscopic calculations.