Low-lying dipole modes in vibrational nuclei studied by photon scattering

After a short introduction to the nuclear resonance fluorescence technique (NRF) and a brief description of typical photon scattering facilities, the present topical review-focuses on three phenomena observed in recent NRF experiments on nuclei near the shell closures. These topics of current interest in low-energy nuclear structure physics are: the systematics of 1(-) quadrupole-octupole-coupled two-phonon states (2(+) circle times 3(-)), the study of two-phonon mixed-symmetry states and the exploration of the E1 pygmy resonance near the particle emission threshold.