Elsevier

Nuclear Physics A

Volume 599, Issues 3–4, 25 March 1996, Pages 560-578
Nuclear Physics A

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

https://doi.org/10.1016/0375-9474(95)00446-7Get rights and content

Abstract

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 Qt 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 h̷ 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 Qt 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., Δβ2β2(h̷ ω = 0) is smaller with increasing N and the corresponding loss of collectivity, Qt 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 Qt 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.

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    1

    Present address: 4612 Highland Ave., Downers Grove, IL 60515, USA.

    2

    Present address: Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA.

    3

    Present address: Royal Institute of Technology, Department of Physics Frescati, Stockholm, Sweden.

    4

    Present address: Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.

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