Excitation of Giant Resonances in LEAD-208 by 200 and 334 Mev Protons.

Polarized protons of 200 and 334 MeV were scattered from a ('208)Pb target in order to study the excitation of low lying collective states, giant resonances and the continuum. Optical model parameters, obtained from fitting eleastic scattering data were used in a macroscopic vibrational model DWBA code to calculate cross sections and analyzing powers. Good fits were obtained for the measured angular distributions for the low-lying collective and giant resonance states. The strength extracted for the 3('-), 2.615 MeV state for both beam energies agrees with the accepted value, and with other similar experiments in the 150 to 800 MeV energy region. At 334 MeV data for the giant quadrupole resonance (GQR) parameters of excitation energy width and energy weighted sum rule (EWSR) depletion agree well with accepted values. In the 200 MeV experiment, the correct excitation energy and width for the GQR was found, but the measured EWSR depletion was low. This low EWSR depletion is due to background subtraction difficulties associated with the poor energy resolution. The 334 MeV work was done at a energy resolution of 80 KeV (FWHM), while the 200 MeV experiment had 1.0 to 1.2 MeV (FWHM) resolution. The continuum underlying the giant resonances was found to arise from quasifree single step nucleon-nucleon scattering.