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, h 9 2 , h 11 2 , i 13 2 and d 5 2 were established to high spin except for the 5 2 + [402] bands. Only the h 9 2 bands show sharp alignment gains compatible with alignment of ( i 13 2 ) 2 neutrons. The smooth apparent alignments of the i 13 2 proton bands can be attributed, at least qualitatively, to a much larger deformation. The complex alignment gains observed in the h 11 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.