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 (π${\mathit{h}}_{9/2}$, π${\mathit{i}}_{13/2}$, π${\mathit{d}}_{5/2}$, π${\mathit{h}}_{11/2}$, and π${\mathit{f}}_{7/2}$) have been established, among which the π${\mathit{f}}_{7/2}$ (1/$2^{\mathrm{-}}$[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 π${\mathit{h}}_{9/2}$ and π${\mathit{i}}_{13/2}$, have been discussed on three aspects: deformation driving, shape evolution, and quasiparticle alignment. It is found that the π${\mathit{i}}_{13/2}$ orbital has a strong, positive-${\mathrm{\beta }}_2$ driving effect on the shape of Ir nuclei, while the driving force of the π${\mathit{h}}_{9/2}$ orbital is minimized when the Fermi level reaches the shell. The total Routhian surface calculations suggest that the π${\mathit{h}}_{11/2}$ and π${\mathit{d}}_{5/2}$ configurations in ${}_{}{}^{179}{}_{}{}^{}\mathrm{Ir}$ possess relatively large ${\mathrm{\beta }}_2$ deformation (∼0.26), which is consistent with the particle-rotor calculations. The possible contribution of the π${\mathit{h}}_{9/2}$ crossing to the gradual alignment gains observed in the π${\mathit{h}}_{11/2}$ and π${\mathit{d}}_{5/2}$ bands is discussed from the influence of deformation and interaction strength. © 1996 The American Physical Society.

• Received 20 December 1995

DOI:https://doi.org/10.1103/PhysRevC.53.2106