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

Dipole and electric quadrupole excitations in Pb-204,Pb-206,Pb-207,Pb-208 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 Pb-208, 14 excited states have been populated; in Pb-206, the decays of 41 states have been detected. Information about 45 heretofore unknown excited states in Pb-204 could be measured as well as eleven known levels in Pb-207. 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. (C) 2003 Published by Elsevier B.V.