Determination of giant resonance strengths

Abstract

Using theoretical strength functions to describe the different giant resonances expected at excitation energies of the order of (60–85) A 1 3 MeV , we calculate the double differential cross sections d 2σ dΩ d E associated with the reactions 208Pb(α, α') and 90Zr (α, α') ( E α = 152 MeV). The angular distributions for the giant quadrupole and giant monopole resonances obtained from fits to these spectra, making simple, commonly used assumptions for the peak shapes and background, are compared to the original angular distributions. The differences between them are an indication of some of the uncertainties affecting the giant resonance strengths extracted from hadron inelastic scattering data. Fits to limited angular regions lead to errors of up to 50% in the value of the energy-weighted sum rule, depending on the angles examined. While it seems possible to extract the correct EWSR for the GMR by carrying out the analyses at 0°, no single privileged angle seems to exist in the case of the GQR.