Dipole State in Nuclei

It is shown that the energies of the positions of singleparticle excitations lying between zero bombarding energy and the binding energy of the last neutron cannot be compared directly due to dipole absorption. Because many particle-hole states can be formed, with the states almost degenerate in energy, the particle-hole interaction can have a profound effect in redistributing dipole transition strength. These effects are demonstrated by a schematic model which shows how coherent effects are able to push the dipole transitions to high energies. Protons in a potential well are considered, and the discussion is extended to protons and neutrons in a nucleus. The discussion is limited to nuclei with double closed shells, neglecting the influence of the few valence nucleons, spin, and considering only transitions from 1 to 1 + 1. (C.J.G.)