High-spin structures in 137Sm: Role of the β-driving νi/sub 13/2/ intruder in deformation enhancement

Collective band structures have been observed in the neutron-deficient 137Sm nucleus by means of the 104Pd(37Cl,p3nγ) reaction. At lowspins, the yrast band, built on the νh/sub 11/2/[514]9/2/sup -/ Nilsson orbital, exhibits a large signature splitting (similar to 100 keV) consistent with a significant triaxial shape (γ similar to -20 degree). 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/sub 11/2/ protons which drive the nucleus towards the prolate (γ=0 degree) shape. In addition, a decoupled band was observed built on an I/sup π/= (17/2+) state. This band reveals a 50% increase in the dynamic moment of inertia consistent with an enhanced quadrupole deformation (β similar to 0.35), and is believed to be built on the β-driving νi/sub 13/2/ [660]1/2+ 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 133Ce,135Nd, and 139Gd isotones