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.