High-spin structures in ${}_{}{}^{137}{}_{}{}^{}\mathrm{Sm}$: Role of the β-driving ν$i_{13/2}$ intruder in deformation enhancement

Collective band structures have been observed in the neutron-deficient ${}_{}{}^{137}{}_{}{}^{}\mathrm{Sm}$ nucleus by means of the ${}_{}{}^{104}{}_{}{}^{}\mathrm{Pd}$${(}^{37}$Cl,p3nγ) reaction. At low spins, the yrast band, built on the ν$h_{11/2}$ [514]${(9/2\mathrm{}}^{\mathrm{-}}$ Nilsson orbital, exhibits a large signature splitting (∼100 keV) consistent with a significant triaxial shape (γ∼-20°). At higher spins, two sidebands were observed which are characterized by strong ΔI=1 transitions and a lack of signature splitting. These band structures contain rotationally aligned lower-midshell $h_{11/2}$ protons which drive the nucleus towards the prolate (γ=0°) shape. In addition, a decoupled band was observed built on an $I^{\pi }$= ${\left(\right(17/2\mathrm{}}^{+}$) state. This band reveals a 50% increase in the dynamic moment of inertia consistent with an enhanced quadrupole deformation (β∼0.35), and is believed to be built on the β-driving ν$i_{13/2}$ [660]${(1/2\mathrm{}}^{+}$ single-quasiparticle state, intruding from two harmonic oscillator shells above. The β-driving properties of this orbital represent an important mechanism in the evolution of enhanced nuclear deformation in this region. The results are compared to those of the N=75 ${}_{}{}^{133}{}_{}{}^{}\mathrm{Ce}$, ${}_{}{}^{135}{}_{}{}^{}\mathrm{Nd}$, and ${}_{}{}^{139}{}_{}{}^{}\mathrm{Gd}$ isotones.