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

Abstract

We report the observation of the giant dipole resonance in Pb nuclei near A\ensuremath{\sim}200 at excitation energies of 66, 88, and 103 MeV and with average angular momenta of 25\ensuremath{\Elzxh} to 44\ensuremath{\Elzxh}. 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 \ensuremath{\beta}apeq20.3. These results are compared with a prediction for superdeformed shapes in $^{196}\mathrm{Pb}$ at L=30\ensuremath{\Elzxh}.