Spectroscopy of 175Ir and 177Ir and deformation effects in odd iridium nuclei

Excited states in 175Ir and 177Ir have been identified using (heavy ion, pxn) reactions and γ-ray spectroscopic techniques. Rotational bands based on intrinsic states arising from the odd-proton parents, were established to high spin except for the 5/2+[402] bands. Only the h9/2 bands show sharp alignment gains compatible with alignment of the i13/2 proton bands can be attributed, at least qualitatively, to a much larger deformation. The complex alignment gains observed in the h11/2 bands in these and other iridium isotopes in the range 173-181Ir are consistent with the effects of mixing with a deformed intruder (equivalently, a low-spin shape change). This conjecture is tested against the in-band decay properties using a three-band model. Examination of the band structure suggests a significant gamma deformation at very low spin, before the change to a more deformed configuration occurs. 31 refs., 6 tabs., 14 figs