Damping of giant resonances in hot nuclei

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Abstract
The effect of one- and two-body dissipation on the damping of giant dipole resonances (GDR’s) is studied in a semiclassical approach solving a Vlasov equation with a collision relaxation time. The latter is microscopically evaluated from the equilibration of a distorted momentum distribution in a kinetic approach. Temperature effects are introduced in the initial distribution function and in Pauli blocking rearrangement in the path to equilibration. Particle emission is also computed in the same microscopic picture. Without free parameters a good agreement with data is obtained for GDR’s on the ground state. For collective vibration built on excited states we get a dramatic increase of the widths due to the enhancement of nucleon-nucleon (NN) collisions. The saturation observed in some experiments is explained as due to the competition of particle evaporation which cools down the system. The transition to first-sound modes is ruled out for the persistence of long-nucleon mean free paths at relatively high temperatures.