The Photoresponse of Atomic Nuclei: Collective Excitations and Photodissociation

The dipole strength distribution of atomic nuclei below the particle threshold has been investigated systematically in photon scattering experiments. A concentration of electric dipole strength around 7 MeV exhausting up to 1% of the Energy Weighted Sum Rule has been observed in all nuclei studied so far. The detailed structure of these excitations and the connection to a resonance‐like concentration of E1 strength above the threshold found in neutron‐rich radioactive nuclei is still not understood. The latest strength measurements and new experiments with hadrons to study the isospin character of the excitations are discussed.