Two-phonon background for the double giant resonance

Abstract

The direct excitation of a "sea" of two-phonon configurations above 15 MeV from the ground state is considered. It is concluded that these configurations form a flat physical background in photoexcitation cross sections and Coulomb excitation in heavy ion reactions at relativistic energies. The contribution of the background to the total cross section in Coulomb excitation of Pb-208 in the DGDR energy region is about 15%. This shows that It should be considered while drawing out conclusions on anharmonicities effects for the DGDR.