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Polarization asymmetries observed in elastic tagged photon scattering at excitations between 16 and 30 MeV were used to identify the isovector giant electric quadrupole resonance in 208 Pb through its interference with underlying electric dipole strength. Resonance parameters reflecting the distribution of the El (T~\) transition strength were extracted in a manner that has minimal sensitivity to uncertainties in the Delbruck amplitudes or in the q dependence of the modified Thomson amplitudes. The isovector £2 resonance was found at an excitation of 20.2 ±0.5 MeV, with a width of 5.5 ±0.5 MeV, and a strength corresponding to 1.4 ± 0.3 times the isovector quadrupole sum rule. PACS numbers: 24.30.Cz, 24.70. +s, 25.20.Dc, 27.80.+W

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