GIANT-DIPOLE RESONANCE BUILT ON HIGHLY EXCITED-STATES OF SN-120 NUCLEI POPULATED BY INELASTIC ALPHA-SCATTERING

High energy gamma rays from the decay of the giant resonance in hot Sn -120 nuclei were measured in the excitation energy range of 30-130 MeV . The excited nuclei were populated by inelastic scattering of a parti cles at 40 and 50 MeV/nucleon. The resonance width was observed to inc rease monotonically with increasing excitation energy, from 5 MeV at t he ground state to similar to 12 MeV at the largest excitation energy. Inelastic scattering predominantly populates low angular momentum sta tes, and the observed width increase is thus attributed to fluctuation s in the nuclear shape induced by temperature.