Octupole correlations in N=88Dy154 : Octupole vibration versus stable deformation

Abstract

We report on low-spin states of $^{154}\mathrm{Dy}$ populated via the reaction $^{155}\mathrm{Gd}$ $(^{3}\mathrm{He},4n)$ with a beam energy of 37.5 MeV from the Separated Sector Cyclotron at iThemba Laboratory. The AFRODITE \ensuremath{\gamma}-ray spectrometer was used to establish new $E1$ transitions between bands of opposite parity. The measurements broaden the $N=88$ systematics on the relationship between the first excited positive-parity pairing isomer band and the lowest-lying negative-parity band as the nuclear quadrupole deformation decreases with increasing proton number. In a region of strong octupole correlations the data suggest that the spectroscopy of $N=88$ nuclei is driven by stable octupole deformations and not by vibrations.