ABSTRACT
The situation is different when the system becomes internally excited, in keeping with the fact that temperature can be viewed as the energy available to the nucleons to make real transitions into complex configurations, in particular into “doorway” configurations, where the particle has changed its state of motion by setting the nuclear surface into vibration. The appearance of boson occupation factors in the expressions is a consequence of treating all vibrations as phonons, as done in the Random Phase Approximation. The Matsubara techniques can also be applied to the calculation of the self-energy of vibrations arising from the coupling of the modes to “doorway states” containing uncorrected particle-hole excitations and a surface vibrational mode. The presence of collisions and density fluctuations changes the picture in a qualitative way by producing a strongly damped vibration displaying a complicated beating pattern, pointing to the existence of a variety of normal modes.
