Lifetimes of high spin states in an odd-proton nucleus ¹²⁹Cs

Lifetimes of high spin states in ¹²⁹Cs are measured using the Doppler shift attenuation method. The high spin states of ¹²⁹Cs are populated following the fusion evaporation reaction ¹²⁴Sn( ¹¹B, 6n)¹²⁹Cs at a beam energy of 65 MeV. The reduced transition probabilities B(E2) and the transition quadrupole moments Q _t in the negative- and positive-parity bands are deduced. The experimental results indicate that the Q_t values of the negative parity band are smaller than those of the positive parity bands, probably due to different γ-deformation driving effects of different proton orbitals. The Q_t values exhibit a considerable increase near the band crossing region in these bands. This behavior demonstrates that nuclear shape changing results from the neutron or proton alignments. The signature splitting of the πh_11/2 and πg_7/2 bands shows the opposite changing trend after backbending due to the h_11/2 neutron and h_11/2 proton alignments, respectively.