Multiple scales in the fine structure of the isoscalar giant quadrupole resonance in Pb-208

The fine structure of the isoscalar giant quadrupole resonance in Pb-208, o bserved in high-resolution (p,p') and (e,e') experiments, is studied using the entropy index method. In a novel way, it enables to determine the numbe r of scales present in the spectra and their magnitude. We find intermediat e scales of fluctuations around 1.1 MeV, 460 keV and 125 keV for an excitat ion energy region 0-12 MeV. A comparison with scales extracted from second RPA calculations, which are in good agreement with experiment, shows that t hey arise from the internal mixing of collective motion with two particle-t wo hole components of the nuclear wavefunction. (C) 2000 Elsevier Science B .V. All rights reserved.