Direct Evidence of Octupole Deformation in Neutron-RichBa144

Abstract

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.

Coexistence and evolution of shapes: mean-field-based interacting boson model

“…6. In general, the theoretical predictions are in good agreement with the experimental results [16], not only for the excitation energies but also for the E2 and E3 transition strengths. We note the very low-lying negative-parity band, which conforms to the results that the corresponding SCMF PES in Fig.…”

Evolution of Octupole Deformation in Radium Nuclei from Coulomb Excitation of Radioactive Ra222 and RaButler1, Gaffney2, Spagnoletti3 et al. 2020Phys. Rev. Lett.Self Cite670390View full textAdd to dashboardCite

“…Evidence has been presented that 224 Ra and 226 Ra have static octupole deformation on account of an enhancement in the E3 moment in these nuclei [2,3]. Large E3 moments have also been recently measured for neutron-rich barium isotopes, suggesting that, within the experimental uncertainty, these nuclei could have octupole deformation [4,5]. The only example of an octupole unstable nucleus other than 226 Ra where stable beams have been used to obtain a complete set of E3 matrix elements is 148 Nd [6].…”

Fast-timing spectroscopy at ISOLDE

“…On one side, the growth of deformation can be studied as Z increases from the Z=28 proton shell closure to the strongly deformed region at 80 Zr (Z=40) [38]. On the other side, the evolution of shell structure in the Ni isotopic chain can be investigated when neutrons are added up to the doubly magic 78 Ni with N=50.…”

“…For the second excited state the half-life of ∼25 ps allows to propose a f 5 2 3 p ( ) configuration and a 3 2 -spin-parity assignment. For the N=49 nucleus 80 Ga, with three proton particles and one neutron hole outside the doubly magic core, the forecast configurations arise from the coupling of a f 5 2 p particle and a g 9 2 n hole. In a recent investigation by γ and fast-timing spectroscopy [60], the spinparity of the ground state was firmly assigned to be 6 -, and the previously unknown excitation energy of the low-lying isomer observed by collinear laser spectroscopy [61] was established at 22.4keV, in agreement with shell-model calculations.…”