COULOMB FRAGMENTATION AND COULOMB FISSION OF RELATIVISTIC HEAVY-IONS AND RELATED NUCLEAR-STRUCTURE ASPECTS

The Coulomb excitation of Pb-208 projectiles has been studied at an en ergy of 640 A MeV. Cross sections for the excitation of the two-phonon giant dipole resonance were measured for different targets, and show clear evidence for a two-step electromagnetic excitation mechanism. Th e experimental cross sections exceed those calculated in the harmonic oscillator approximation by a factor of 1.33 +/- 0.16. The deduced 2 g amma-decay probability is consistent with the expectation in the harmo nic limit. Finally, the excitation of the two-phonon giant dipole reso nance in the deformed and fissile nucleus U-238 is discussed.