Identification of the 2_{1,ms}^{+} mixed-symmetry state in ^{136}Ce

The evolution of the one-quadrupole phonon mixed-symmetry state is important for understanding the role of the quadrupole proton-neutron interaction in the valence shell. To study the evolution of the 2(1,ms)(+) mixed-symmetry state in the N = 78 isotones above Z = 50, a Coulomb excitation measurement was performed to identify the 2(1,ms)(+) state in Ce-136 by measuring absolute transition strengths. The 2(1,ms)(+) state was found to be predominantly concentrated in the 2(4)(+) state of this nucleus. The simple picture of shell stabilization given to account for the fragmentation of the strength observed in Ce-138 does not seem to apply to Ce-136.