The loss of collectivity at high spins in 164Yb and its neighboring even-even nuclei

• Published in: Nuclear physics. A 1996-03, Vol.599 (3), p.560-578
• Main Authors: Xie, H., McGowan, F.K., Baktash, C., Garrett, J.D., Hamilton, J.H., Johnson, N.R., Lee, I.Y., Wells, J.C., Wyss, R., Yu, C.-H.
• Format: Article
• Language: English
• Subjects: Nuclear reactions
• ISSN: 0375-9474
• DOI: 10.1016/0375-9474(95)00446-7

Lifetimes of high-spin states in 164Yb have been measured by the Doppler-broadened line shape (DBLS) method using the reaction 124Sn( 44Ca, 4n) 164Yb at a bombarding energy of 189 MeV. The Q t values from the data decrease sharply over the rotational frequency range 0.3 to 0.5 MeV ( I = 20 to 32 ħ). At the same rotational frequencies the kinematic moment of inertia is nearly constant, increasing slightly at the higher frequencies h ̷ ω = 0.40 to 0.55 MeV . These observations can be understood qualitatively as a rotationally-induced deoccupation of strongly shape polarizing anti-aligned high- j, low-Ω orbitals i.e., those in which the nucleons are moving in the opposite direction to the rotation. A summary of the Q t values extracted from the lifetime data for the yrast decay sequences of the even- A nuclei 160–168Yb are compared with the deformations from self-consistent cranking TRS calculations. The TRS calculations show the expected neutron number dependence, i.e., Δβ 2 β 2 ( h ̷ ω = 0) is smaller with increasing N and the corresponding loss of collectivity, Q t vs ħ ω, has a smaller slope at the larger ħ ω with increasing N. For 164,166,168Yb the loss of collectivity from the DBLS measurements occurs at higher ħ ω than predicted and the slope of Q t vs ħ ω is much larger than predicted. The enhanced E1/E2 branching ratios and the large transition dipole moments for decay of the states in the (−, 1) band to the ground band and the (+, 0) band in 164Yb suggest an octupole instability for 164Yb.