Excited negative parity bands in¹⁶⁰Yb

Abstract

Negative parity rotational bands in 70 160 Yb 90 nucleus have been studied. They were populated in the 148 Sm( 16 O, 4n) 160 Yb reaction at 90 MeV. The gamma-coincidence data have been collected using Indian National Gamma Array composed of twenty Compton suppressed clover germanium (Ge) detectors. Double gating on triple gamma coincidence data were selectively used to develop the decay scheme for these negative parity bands by identifying and taking care of the multiplet transitions. The even-and odd-spin negative parity bands in 160 Yb have been studied by comparing the reduced transition probability ratios with the similar bands in neighbouring even-even rare earth nuclei. It is concluded that the concerned odd-spin and evenspin bands are not signature partners and that their structures are compatible with those of the 'pear-shape' and 'pyramid-shape' oscillations, respectively, the octupole shapes superposed with the quadrupole shape of the ground-state.

Spectroscopy of a tetrahedral doubly magic candidate nucleus ${}_{70}^{160}{\mathrm{Yb}}_{90}$

“…The odd-spin Band-5 and the even-spin Band-6 are connected mainly to the yrast band (Band-1) by several ΔI=1 and ΔI=0 E1-transitions, respectively which is shown in figures 9 and 10. The structure of Band-5 as observed in the present work, has been discussed separately in [46] along with another band that was reported earlier [4] but not observed in the present experiment. The structure of Band-6 has been illustrated in figure 15.…”

“…So, the structure of Band-5 could not be confirmed as of a traditionally known rotationally aligned octupole phonon. Also, the intensity ratios of the intra-band γ-transitions from Band-5 and comparison with a number of odd-spin negative-parity bands in neighbouring nuclei with Z and N close to 70 and 90, respectively, suggests that Band-5 and Band-6are not signature partners, seerecent [46]. Instead, as argued in this article, whereas the behaviour of Band-5 is compatible with that of a pear-shape octupole one-phonon vibration band, Band-6 could be its analogue in that the Y 30 -vibration is replaced by the Y 32 -vibration.…”