MULTIPHONON GIANT-RESONANCES

A new class of giant resonances in nuclei is discussed, i.e. giant res onances built on other giant resonances. These resonances are observed with very large cross sections in relativistic heavy ion collisions. A great experimental and theoretical effort is underway to understand the reaction mechanism which leads to the excitation of these states i n nuclei, as well as the better microscopic understanding of their pro perties, for example, strength, energy centroids, widths and anharmoni cities.