Lifetimes of Excited Levels in 131Ce

The fusion-evaporation reaction 116Sn ( 19F, p3n) 131Ce at projectile energy of 95 MeV is used to populate high spin states in 131Ce. The de-exciting γ-rays are detected in γ-γ coincidence measurement with Compton-suppressed BGO-HPGe detectors. Level lifetimes of 131Ce were determined by using the Doppler shift attenuation method. The experimental results indicate that collectivity of 131Ce is reduced relative to that of 130Ce and it follows that deformation decreases with increase of the neutron number on the basis of systematic comparison of transition quadrupole moments for the light cerium isotopes.