Experimental Observation of High Spin States in ~(135)La Nucleus

High spin states of 135La have been experimentally studied by using 128Te(10B, 3n) 135La reaction at 46 MeV beam energy. Based on the γ-γ coincidence relationships, relative intensities and ADO ratios, a level scheme of 135La has been established. Both signature components of the πh-11/2 negative-parity band and a band crossing at ω≈0 40MeV were observed. In view of the systematics of the N=78 isotones, this backbending is proposed to be caused by the alignment of a pair of πh-11/2 protons. The πh-11/2 protons drive the nuclear core towards γ≈0°, the collective prolate shape. In addition, a ΔI=1 negative-parity band with strong M1 transitions and a very small signature splitting was observed. Comparing with the systematic features of ΔI=1 bands in neighboring odd-proton nuclei in this mass region, the πh-11/2(νh-11/2)2 configuration was assigned to the ΔI=1 bands of 135La. The alignment of the h-11/2 neutron pair drives the nuclear core towards γ≈-60°, the collective oblate shape.