Doorway concept at high excitation energy

The spreading of transition strength is studied in the doorway picture by t aking the coupling to the continuum explicitly into account. The internal ( configurational) coupling mixes the doorway state with the background state s and is responsible for all the states actually having a decay width. Ther efore, external mixing of the states via the continuum is induced. If it is large, resonance trapping appears and the slates will be demixed. Thus the residual interaction is effectively reduced. As a consequence, the spreadi ng of transition strength can be small also at high excitation energy. The relation to the golden rule is discussed. [S0556-2813(99)02001-4].