Effects of intruder states inIr179

Abstract

High-spin states of the odd-A $^{179}\mathrm{Ir}$ have been studied via heavy-ion fusion reaction. Bands built on five different Nilsson states (\ensuremath{\pi}${\mathit{h}}_{9/2}$, \ensuremath{\pi}${\mathit{i}}_{13/2}$, \ensuremath{\pi}${\mathit{d}}_{5/2}$, \ensuremath{\pi}${\mathit{h}}_{11/2}$, and \ensuremath{\pi}${\mathit{f}}_{7/2}$) have been established, among which the \ensuremath{\pi}${\mathit{f}}_{7/2}$ (1/${2}^{\mathrm{\ensuremath{-}}}$[530]) band is identified for the first time in Ir isotopes. Experimental aligned angular momenta, band-crossing frequencies, and relative transition rates are analyzed and compared with the cranked shell model and the particle-rotor model calculations. Effects of intruder states, particularly \ensuremath{\pi}${\mathit{h}}_{9/2}$ and \ensuremath{\pi}${\mathit{i}}_{13/2}$, have been discussed on three aspects: deformation driving, shape evolution, and quasiparticle alignment. It is found that the \ensuremath{\pi}${\mathit{i}}_{13/2}$ orbital has a strong, positive-${\mathrm{\ensuremath{\beta}}}_{2}$ driving effect on the shape of Ir nuclei, while the driving force of the \ensuremath{\pi}${\mathit{h}}_{9/2}$ orbital is minimized when the Fermi level reaches the shell. The total Routhian surface calculations suggest that the \ensuremath{\pi}${\mathit{h}}_{11/2}$ and \ensuremath{\pi}${\mathit{d}}_{5/2}$ configurations in $^{179}\mathrm{Ir}$ possess relatively large ${\mathrm{\ensuremath{\beta}}}_{2}$ deformation (\ensuremath{\sim}0.26), which is consistent with the particle-rotor calculations. The possible contribution of the \ensuremath{\pi}${\mathit{h}}_{9/2}$ crossing to the gradual alignment gains observed in the \ensuremath{\pi}${\mathit{h}}_{11/2}$ and \ensuremath{\pi}${\mathit{d}}_{5/2}$ bands is discussed from the influence of deformation and interaction strength. \textcopyright{} 1996 The American Physical Society.