The ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$${(}^{30}$Si,5n${)}^{179}$Os reaction has been used to study rotational bands at high spin by means of extensive gamma-ray coincidence measurements. The new α=-1/2 signature partner of the 1/$2^{\mathrm{-}}$[521] band has been found up to spin 31/$2^{\mathrm{-}}$ and the previously known α=+1/2 partner extended up to spin 45/$2^{\mathrm{-}}$. The α=-1/2 and α=+1/2 components of the previously known 7/$2^{\mathrm{-}}$[514] and the 9/$2^{+}$[624] bands were extended up to spins 63/$2^{\mathrm{-}}$, 53/$2^{\mathrm{-}}$ and 63/$2^{+}$,61/$2^{+}$, respectively. The two components of the newly found band 5/$2^{\mathrm{-}}$[512] have been established up to spins 59/$2^{\mathrm{-}}$ and 65/$2^{\mathrm{-}}$. In addition, two other new bands were found, one of them with spins up to 61/$2^{+}$ decays to the 9/$2^{+}$[624] band. Configurations have been proposed by comparing the signature splittings and the B(M1)/B(E2) ratios with the theoretical predictions. The latter points to rather strong Coriolis interaction between the 5/$2^{\mathrm{-}}$[512] and 7/$2^{\mathrm{-}}$[514] bands. The first band crossing observed in nine out of the ten bands is most probably due to the alignment of a pair of ${\mathit{i}}_{13/2}$ neutrons, on the basis of a comparison of experimental Routhians with the cranking shell model calculations. In the three positive-parity sequences and in the α=+1/2 signature of the 5/$2^{\mathrm{-}}$[512] band, second band crossings are also observed that are suggested to be caused by an alignment of two ${\mathit{h}}_{9/2}$ protons.

• Received 30 March 1992

DOI:https://doi.org/10.1103/PhysRevC.46.1642