Collective response of nuclei: Comparison between experiments and extended mean-field calculations

Abstract

The giant monopole, dipole, and quadrupole responses in ${}^{40}\mathrm{Ca},$ ${}^{90}\mathrm{Zr},$ ${}^{120}\mathrm{Sn},$ and ${}^{208}\mathrm{Pb}$ are investigated using linear response treatment based on a stochastic one-body transport theory. Effects of the coupling to low-lying surface modes (coherent mechanism) and the incoherent mechanism due to nucleon-nucleon collisions are included beyond the usual mean-field description. We emphasize the importance of both mechanisms in the fragmentation and damping of giant resonance. Calculated spectra are compared with experiment in terms of percentage of energy-weighted sum rules in various energy regions. 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 ${}^{40}\mathrm{Ca}$ is correctly reproduced. In addition, the appearance of fine structure in the response ${}^{208}\mathrm{Pb}$ is partly described by the calculations in which the coherent mechanism plays an important role.