Low energy Q-phonon excitations in nuclei

One-, two-, and multi-Q-phonon excitations in heavy nuclei are discussed. We describe the Q-phonon scheme for low-lying, isoscalar, positive parity states in γ-soft nuclei and compare the predictions of the Q-phonon scheme to new data on the nucleus 132Ce. We report on the experimental proof for the quadrupole-octupole coupled two-phonon nature of the lowest-lying 1- state in the semi-magic N=82 nuclei 142Nd and 144Sm. Finally, low-lying proton-neutron asymmetric mixed-symmetry states are discussed in terms of the Q-phonon scheme. We report on recent lifetime measurements of the mixed-symmetry one-Q-phonon excitation, the 2ms+ state, in the nuclei 125,128Xe, 136Ba, and 144Nd. (c) 1999 American Institute of Physics