Quadrupole and octupole collectivity in Ba143

Abstract

The neutron-rich barium nuclei have been the subject of intense interest due to the enhanced octupole correlations they are predicted to exhibit. The observation of enhanced octupole collectivity in 144,146 Ba as measured in sub-barrier Coulomb excitation, consistent with static octupole deformation, has further heightened this interest. In the present work, these studies are extended to the neighboring odd-mass 143 Ba to investigate the interplay between single-particle and collective octupole degrees of freedom. A new measurement of the first 9 2 − -state lifetime is also presented. Reflection-Asymmetric Triaxial Particle Rotor Model calculations indicate that the negative-parity bands in 143 Ba can be understood as a decoupled structure of νh 9/2 parentage, while the positive-parity bands are built on a decoupled octupole phonon. No evidence for E3 excitation is observed in this work, but an upper limit is placed on the E3 matrix element to the lowest octupole band.

$^{145}$Ba and $^{145, 146}$La structure from lifetime measurements

“…Thus, despite the predictions, the permanent octupole deformation in the region remains an incognita for these odd and odd-odd nuclei. As an example to illustrate this problem, a recent work in which 143 Ba was measured using Coulomb excitation was unable to draw firm conclusions on static octupole deformation despite having measured B(E3) values [53]. The authors argued that several low-lying states had unknown or tentative spin and parities, making any interpretation highly speculative.…”