Effects Of Intruder States In Ir-179

High-spin states of the odd-A Ir-179 have been studied via heavy-ion fusion reaction. Bands built on five different Nilsson states (pi h(9/2), pi i(13/2), pi d(5/2), pi h(11/2), and pi f(7/2)) have been established, among which the pi f(7/2) (1/2(-)[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 pi h(9/2) and pi i(13/2), have been discussed on three aspects: deformation driving, shape evolution, and quasiparticle alignment. It is found that the pi(13/2) orbital has a strong, positive-beta(2) driving effect on the shape of Ir nuclei, while the driving force of the pi h(9/2) orbital is minimized when the Fermi level reaches the shell. The total Routhian surface calculations suggest that the pi h(11/2) and pi d(5/2) configurations in Ir-179 possess relatively large beta(2) deformation (similar to 0.26), which is consistent with the particle-rotor calculations. The possible contribution of the pi(9/2) crossing to the gradual alignment gains observed in the pi h(11/2) and pi d(5/2) bands is discussed from the influence of deformation and interaction strength.