Quadrupole Moment of the h_11/2 Quasineutron Band in ¹²⁹Ce

Mean lifetimes of the h_11/2 quasineutron band in ¹²⁹Ce were measured by using the Doppler shift attenuation method in connection with the reaction ¹¹⁶Sn (^l6O, 3n)¹²⁹Ce at a bombarding energy of 73MeV. The data indicate that transition quadrupole moment of ¹²⁹Ce is smaller than that of ¹²⁸Ce. This reduction in collectivity caused by the addition of an h_11/2 neutron can be interpreted as due to triaxiality induced by γ driving effect.