Experimental Study of High-Spin States in Deformed Odd-Odd¹⁸⁰Ir

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 _5/2and πi _13/2bands 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.