Collective response of nuclei: Comparison between experiments and extendedmean-field calculations - art. no. 064305

The giant monopole, dipole, and quadrupole responses in Ca-40, Zr-90, Sn-12 0. and Pb-208 are investigated using linear response treatment based on a s tochastic one-body transport theory. Effects of the coupling to low-lying s urface modes (coherent mechanism) and the incoherent mechanism due to nucle on-nucleon collisions are included beyond the usual mean-field description. We emphasize the importance of both mechanisms in the fragmentation and da mping of giant resonance. Calculated spectra are compared with experiment i n terms of percentage of energy-weighted sum rules in various energy region s. We obtain reasonable agreement in all cases. Special attention has been given to the fragmentation of the giant quadrupole resonance in calcium and lead. In particular, the equal splitting of the 2(+) in Ca-40 is correctly reproduced. In addition. the appearance of fine structure in the response Pb-208 is partly described by the calculations in which the coherent mechan ism plays an important role.