Comment on the characterization of the giant quadrupole resonance in /sup 208/Pb as reported from π+/π- scattering

Studies of π+/π- inelastic excitation of the giant quadrupole resonance in /sup 208/Pb have been interpreted as implying a quadrupole matrix element ratio for neutron to proton excitations of M/sub n//M/sub p/ = 3.8, and a reduced electric transition rate of B(E2)up-arrow = 1010 +- 600 e2fm4. These values are in strong disagreement with the results of a large body of inelastic light-ion scattering data as well as recent electron scattering results, all of which are consistent with a predominantly isoscalar character for this resonance. A similar situation prevails for the scattering of 400-MeV /sup 16/O and 1428-MeV /sup 17/O ions where Coulomb excitation is important, and the inelastic cross sections are very sensitive to B(E2)up-arrow as well as the hadronic interaction strength. Studies of the photon decay of the giant quadrupole resonance are also in good agreement with random phase approximation calculations that imply a predominantly isoscalar character; this agreement would be destroyed if the interpretation of the pion experiment were correct