Octupole correlations in neutron-rich145,147Lanuclei: Coriolis-limit-coupling bands with aligned

Abstract

Several new high-spin states are observed in the prompt ␥-rays emitted from the neutron-rich, odd-Z 145,147 La fragments produced in the spontaneous fission of 252 Cf. Alternating parity bands are extended up to spins 41/2 and 43/2 in 145,147 La, respectively. A new band completes the evidence for two sets of parity doublets expected for octupole correlations. Eight B(E1)/B(E2) ratios ͑four new͒ between two bands in 145 La are all essentially constant and somewhat larger than similar ratios in 143,144 Ba, where stable octupole deformation and/or correlations are reported. The new ratios out of the 31/2 Ϫ levels in both nuclei show a sharp spike compared to other states, presumably from a strong reduction in E2 strengths in this backbending region. In 145 La, collective bands show competition and coexistence between symmetric and asymmetric shapes. Band crossings occur in both nuclei around បϷ0.26-0.30 MeV. Their backbends are associated with the alignment of two i 13/2 neutrons according to cranked shell model calculations. ͓S0556-2813͑99͒08402-2͔ PACS number͑s͒: 21.10. Re, 23.20.Lv, 27.60.ϩj, 25.85.Ca

High-spin states and a new band based on the isomeric state in 152Nd

“…The projected shell model is employed to study the band structure of this nucleus. The results show that the calculated levels of the bands are in good agreement with the experimental ones, and the isomeric state and the negative-parity band are based on the proton π5/ The neutron-rich nuclei around the A ∼ 150 region show transitional character from spherical to prolate quadrupole deformation and from octupole vibrational excitations to static octupole deformation [1][2][3][4][5].152 Nd is located in the deformed region and has a well-deformed shape. Previously, the level structure of 152 Nd has been studied by using various experimental methods [6][7][8][9][10][11][12].…”

“…The neutron-rich nuclei around the A ∼ 150 region show transitional character from spherical to prolate quadrupole deformation and from octupole vibrational excitations to static octupole deformation [1][2][3][4][5].…”

Identification of new transitions and mass assignments of levels inPr143–153

“…As discussed in Ref. [4], cranked shell model calculations [21] suggest that this backbending at 0.27 MeV originates from the alignment of a neutron i 13/2 pair and not a proton h 11/2 pair. Thus, band (2) in 149 Pr can also be another signature of band (1).…”

“…14 based on the structure similarity to the h 11/2 signature s=+i octupole bands "(1)" and "(2)" in Ref. [21]. When octupole deformation or octupole correlations are strong, one expects a symplectic quantum number s=i, two bands of opposite parity with the spin show in Fig.…”

Reinvestigation of high spin states and proposed octupole correlations inCe147

“…For the odd-A nuclei in this region, octupole deformation and octupole correlations have also been identified in several nuclei, e.g. in 141 Cs [15], 143 Ba [16], 145,147 La [17], 145 Ce [18] and 147 Nd [18].…”