Search for correlations between prolate-shape collective and oblate-shape non-collective nuclear rotation: High-spin states in 159,160Yb

Diverse collective excitations in159Erup to high spin

“…The diverse nature of collective motion in the rare-earth nuclei around A = 160 at high spin make this mass region an excellent testing ground for such models which attempt to explain the deformed nuclear shapes that they exhibit and their behavior in terms of the underlying single-particle configurations. An example of this diverse nature is the observation that collective rotational bands appear to terminate at discrete states around spin 40h in nuclei with N ∼ 90 [1][2][3][4][5][6][7][8][9][10][11]. This has been interpreted as a dramatic change in structure from a collective prolate shape to an oblate single-particle shape via the mechanism of band termination [12,13].…”

High-spin states inYb156and structure evolutions at large angular momenta in even-AYb isotopes

“…5, the first i 13/2 neutron band crossings in the 158,160,162,164 Yb isotopes occur around almost same rotational frequencies 0.27 MeV [10,18,[26][27][28], although these nuclei have different quadrupole deformations [12][13][14]. The constant crossing frequency has been explained in term of the compensation between the decrease in the neutron pair gap and the decrease in the alignment of the i 13/2 neutron pair with increasing neutron number [29], while the sharpness evolution of these first backbends observed in the Yb isotopes may correspond to the oscillations with neutron number of the interaction matrix element between the ground band and the aligned (vi 13/2 ) 2 band [30].…”

“…In Refs. [10,27], the second yrast band crossings observed at rotational frequency 0.42 MeV in 160 Yb [10] and rotational frequency 0.46 MeV in 162 Yb [27], respectively, have been suggested to correspond to the alignment of a pair of h 11/2 protons, which was also predicted by the theoretical calculations [31]. In the earlier studies for the 158 Yb [32,33], the high-spin states with spin = 26 + -36 + in 158 Yb were found to exhibit a nearly vibrational excitation pattern, which was interpreted in terms of a gradual transition toward oblate shape and a band termination occurring at spin = 36 + .…”

“…This shape change was also predicted by the theoretical calculations within the cranking approximation using the generalized Strutinsky methods [17] and has been observed in some experimental studies. For example, the spectroscopy studies of 160 Yb by Byrski et al [10] indicated that the nuclear shape will arrive γ = 60 • around spin 36 + and band termination occurs. This process will produce a pronounced reduction in the collcetivity, which was observed by the following measurements of lifetimes of 160 Yb yrast states at high rotational frequencies [38].…”

Structure changes inEr160from low to ultrahigh spin

“…At higher spin, the yrast structure of these nuclei can undergo a dramatic change with the transition from a prolate to an oblate shape [5][6][7][8][9][10][11][12][13]. Here non-collective single-particle configurations become energetically favored via the mechanism of band termination [14,15].…”