VIBRATIONAL-STATES IN NUCLEI - GIANT-RESONANCES AND MULTIPHONONS

Giant resonances and multiphonons states are nuclear excitations which are interpreted as collective excitations of the constituant nucleons. Their study yields information on the structure of the nucleus and on the dynamical properties of nuclear matter. Over the last twenty years these states have been widely studied, both theoretically and experimentally. The aim of this article is not to present a complete review, but rather to infer from the most recent results the main future direction of research concerning giant electric resonances. Using the results of inclusive experiments, in particular with intermediate energy heavy ion probes, we will draw the main conclusions and discuss the remaining open problems. A major step towards the understanding of these vibrational modes was accomplished through the study of their decay which gives access to their microscopic description. As an illustration, several major measurements of the decay of giant resonances by light particles and gamma rays will be presented. We will show how these results lead to new experiments attempting to establish the origin of resonant states, such as multiphonon states, located at higher excitation energies. The current status of these pioneering studies will be presented and discussed.