Rotational states in neutron-deficientGd139

States have been established in the neutron-deficient ${}_{}{}^{139}{}_{}{}^{}\mathrm{Gd}$ nucleus for the first time via the ${}_{}{}^{92}{}_{}{}^{}\mathrm{Mo}$ ${(}^{50}$Cr,2pnγ) reaction. Both γ-γ and γ-n coincidence techniques were employed. The yrast band, built on the ν$h_{11/2}$ ${\left[514\right](9/2\mathrm{}}^{\mathrm{-}}$ orbital, shows a signature splitting of ∼100 keV implying a significant triaxial shape. At a rotational frequency ħω∼0.29 MeV a pair of $h_{11/2}$ quasiprotons align. Associated with this alignment are a decrease in the signature splitting, indicating a near-prolate nuclear shape, and an enhancement of the interband M1 transitions relative to the E2 crossovers, which is consistent with a mixed neutron-proton configuration. In addition, a tentative decoupled band showing the characteristics of a band theoretically expected for the β-driving ν$i_{13/2}$ orbital was observed.