Evidence for prolate deformation in highly excited neutron-deficient Pb isotopes

We report the observation of the giant dipole resonance in Pb nuclei near A∼200 at excitation energies of 66, 88, and 103 MeV and with average angular momenta of 25ħ to 44ħ. The fits to the dipole strength distribution require two components indicating a strongly deformed nuclear shape. Using width parameters consistent with the ground-state systematics of heavy deformed nuclei gives $E_1$=11.9 MeV, $E_2$apeq215.6 MeV, and prolate deformation with βapeq20.3. These results are compared with a prediction for superdeformed shapes in ${}_{}{}^{196}{}_{}{}^{}\mathrm{Pb}$ at L=30ħ.