Giant Dipole Resonance Built on Highly Excited States of120Sn Nuclei Populated by InelasticαScattering

High energy γ rays from the decay of the giant resonance in hot ${}^{120}$Sn nuclei were measured in the excitation energy range of 30–130 MeV. The excited nuclei were populated by inelastic scattering of α particles at 40 and 50 MeV/nucleon. The resonance width was observed to increase monotonically with increasing excitation energy, from 5 MeV at the ground state to $\sim 12$ MeV at the largest excitation energy. Inelastic scattering predominantly populates low angular momentum states, and the observed width increase is thus attributed to fluctuations in the nuclear shape induced by temperature.