Analysis of giant resonances in proton,He3, andαscattering and the spin-flip strength inPb208

In an attempt to study isovector spin-flip excitations and to find a consistent picture of giant resonances in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, we analyzed giant resonance data from 172 MeV α scattering, 140 MeV ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ scattering, and 200 MeV proton scattering. Using spectroscopic information from α scattering, a good description of recent ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ scattering data is obtained. A detailed analysis of results from different probes reveals differences between complex particle and proton spectra which are interpreted as due to spin-flip contributions. The spin-flip strength is estimated in a microscopic p-h model. At the scattering angles considered it gives resonant strength at ∼9 MeV dominated by $2^{\mathrm{-}}$ excitations and further gives an increasing continuum yield towards higher excitation energies. The cross sections of these spin-flip excitations in (p,p’) are comparable to giant resonance yields and have to be considered in order to obtain a description consistent with complex particle spectra. The continuum part of isoscalar excitations is rather different from that of isovector spin-flip excitations. These features are qualitatively understood from the nuclear matter response. Calculations using the semi-infinite nuclear slab model of Esbensen and Bertsch give an almost quantitative description of isoscalar and spin-isospin continuum.