Multi-quasiparticle states and -forbidden transitions in Os

Shizuma, Toshiyuki; Matsuura, Katsuyuki*; Toh, Yosuke   ; Hayakawa, Takehito; Oshima, Masumi; Hatsukawa, Yuichi; Matsuda, Makoto  ; Furuno, Kohei*; Sasaki, Yasuyuki*; Komatsubara, Tetsuro*; Shimizu, Yoshifumi*

High-spin states in Os have been studied using the 170Er(18O,5n) reaction at a beam energy of 85 MeV. Nine rotational bands based on 1-, 3-, 5- and 7-quasiparticle excitations have been observed. Nilsson configurations are assigned for the newly observed bands using g-factors deduced from M1/E2 branching ratios within the bands. In addition, two isomers with K=(43/2+) and (43/2-) have been identified. The K=(43/2+) isomer decays directly to the K=9/2+ ground state band with a large difference in the quantum number, 17. The decay rates are disccused in terms of a tunneling model where high- (isomeric) and low- states interact via fluctuations towards triaxial nuclear shapes.