EVIDENCE FOR 2-PHONON GIANT-DIPOLE EXCITATION FROM INCLUSIVE MEASUREMENTS OF AU-197 TARGET DISSOCIATION

Cross sections for the electromagnetic dissociation of Au-197 targets by 1.7 A GeV Ne-20 and 1 A GeV Kr-86, Au-197 and Bi-209 beams have been measured by an activation method. Weizsacker-Williams calculations show that the experimental ln cross sections can be understood by first order excitation of the giant dipole and the isoscalar giant quadrupole resonance. In contrast, the 3n cross sections show a much stronger Z(proj)- dependence, which can only be explained by a dominant contribution from two-phonon giant dipole excitation.