Contrasting behaviour of proton h 9 2 and h 11/NU> 2 bands in 175,177,179,181Ir interpreted in an intruder model

Abstract

Rotational bands in the odd-proton isotopes 175Ir, 177Ir, 179Ir and 181Ir based on the h 9 2, h 11/NU> 2, i 13 2 and d 11/NU> 2 orbitals have been identified, the first three to high spin. In all cases the h 9 2 band shows backbending with a crossing frequency and alignment gain consistent with that expected from the neutron i2 13 2 alignment. In contrast the h 11/NU> 2 bands (and the fragments of d 11/NU> 2 bands observed) show complex alignment curves. These alignments can be explained using a phenomenological three-band model which incorporates a deformed intruder band, analogous to that proposed in the very light Pt and Os nuclei. Mixed wave functions from the model reproduce the observed B(M1)/B(E2) ratios. The presence of the intruder band in the h 11/NU> 2 and d 11/NU> 2 configurations and its absence in the h 9 2 band is compatible with its proposed association with an (h2 9 2)0 pair excitation. Show more