Configuration-dependent band structures in odd-odd Ir-180

High-spin states in Ir-180 have been investigated by means of in-beam gamma-ray spectroscopy techniques with the (154)sm(P-31,5n gamma)Ir-180 reaction. Excitation functions, x-gamma and gamma-gamma-t coincidences, DCO (directional correlation of gamma rays deexciting oriented states) ratios, and intraband B(M1)/B(E2) ratios were measured. Five rotational bands have been identified and their configurations are proposed on the basis of B(M1)/B(E2) ratios and by comparing the band properties with known bands in neighboring odd-mass and even-mass nuclei. The neutron AB crossing is observed at (h) over bar omega(c)=0.26(1) MeV for the pi1/2(-)[541] x nu1/2(-)[521] and pi1/2(-)[541] x nu5/2(-)[512] bands, respectively. Staggering of levels as a function of the number of neutron pairs is revealed in the pi1/2(-)[541] x nu 1/2(-)[521] doubly decoupled bands of Ir178-186. The gradual alignment gains at low rotational frequencies are observed in the two strongly coupled bands. Band crossings and alignments in Ir-180 a-re discussed with reference to the total Routhian surface and cranked shell model calculations performed for the neighboring odd-mass nuclei.