Nuclear resonance fluorescence experiments on 204,206,207,208Pb up to 6.75 MeV Original Research Article

Dipole and electric quadrupole excitations in 204,206,207,208Pb have been measured up to 6.75 MeV in resonant photon scattering experiments at the superconducting Darmstadt electron linear accelerator S-DALINAC using two Euroball-Cluster detector modules. In 208Pb, 14 excited states have been populated; in 206Pb, the decays of 41 states have been detected. Information about 45 heretofore unknown excited states in 204Pb could be measured as well as eleven known levels in 207Pb. The extracted dipole strength distributions are discussed within phenomenological (“pygmy resonance”) and microscopic models (quasiparticle-phonon model). A strong fragmentation and a small shift of the detected E1 strength towards higher energies is observed with the opening of the neutron shell closure.