Collisional spreading of small amplitude nuclear vibrations

We present a microscopic treatment of the spreading widths of giant resonances - a collisional RPA (with complex frequencies, z=iw+γ) which turns out to have a very simple analytical form. Its essential ingredients are: a) The usual mean field contribution, which reproduces the frequencies of the collisionless RPA and b) non-unitary (collision) contributions which arise from the inclusion of quantum correlation effects in the weak coupling approximation. This collisional RPA equation can be easily put to quantitative use in realistic nuclear structure problems. (orig.)