Damping of small-amplitude nuclear collective motion

A review is given of the present status of the theory of damping of nuclear vibrations. The main focus is on the microscopic description of the damping phenomena. 'One-body dissipation' arising from the nuclear mean field is discussed and confronted with data. It turns out that, especially in heavy nuclei, this process is insufficient to describe observed resonance broadenings. 'Collisional' damping or 'two-body dissipation' is needed to account for the widths. The necessary extensions of mean-field theory and several approximation schemes in the small-amplitude limit are reviewed. Theoretical results in both light and heavy nuclei are discussed.