Experimental Study of High-Spin States in Deformed Odd-Odd ¹⁸⁰ Ir

Abstract: High spin states in deformed odd-odd ¹⁸⁰Ir have been investigated using the ¹⁵⁴Sm (³¹P, 5nγ)¹⁸⁰Ir reaction through the measurements of excitation functions at 150, 155, 160, 165 and 170 MeV beam energies, K X-γ and γ-γ coincidences at 160 MeV. A new level scheme composed of 5 rotational bands has been established. According to the band structure characteristics and the deduced in band B(M1)/B(E2) ratios, the quasiparticle configurations and spin and parity have been proposed to the observed bands. The neutron AB crossing is observed at hω_c≈0.26 MeV for the π1/2^－[541]⊙ν1/2^－[521] and π1/2^－[541]⊙ν5/2^－[512] bands. This AB crossing frequency is close to that in the ν5/2^－[512] band of ¹⁷⁹Os indicating the loss of intruder nature of the π1/2 - orbit. Gradual alignment gain in both the π9/2^－[514]⊙ν7/2⁺[633] and π9/2^－ν5/2^－[512] bands is observed which is similar to the low spin anomaly in alignment in the πh_11/2,πd_5/2 and πi_13/2 bands of neighboring Ir and Re isotopes. Different alignment properties have been discussed in the framework of cranked shell model, and a larger quadrupole deformation is suggested for the bands with π9/2^－[514] orbit involved.