Electro-excitation of giant dipole resonances in medium-heavy,spherical nuclei

The collective intermediate structure of the giant resonances in medium-heavy, spherical nuclei, which was discovered by photonuclear experiments, has been explained nearly quantatively by the collective dynamic theory, which takes into account the coupling of giant-dipole and surface-quadrupole resonance.However, photonuclear experiments determine essentially only the excitation energy and the dipole strength of the various levels. In order to gain more insight into the model, electro-excitation experiments should be carried through. At moderate momentum transfer (q = 1 fm⁻¹ to 1.5 fm⁻¹), such experiments could test the details of the transition charge distribution predicted by the collective theory. Since the various giant resonance levels have different admixtures of surface phonons, their transition densities and therefore the resulting cross sections show a different behaviour.