Probing nuclear shapes close to the fission limit with the giant dipole resonance in 216Rn

The gamma-ray decay of the giant dipole resonance (GDR) in the compound nucleus 216Rn formed with the reaction 18O+198Pt at the bombarding energy of 96 MeV was investigated. High-energy gamma-ray spectra in coincidence with both prompt and delayed low-energy transitions were measured. The obtained GDR width at the average temperature ⟨T⟩≈1 MeV was found to be larger than that at T=0 MeV and to be approximately constant as a function of spin. The measured width value of 7 MeV is found to be consistent with the predictions based on calculations of the nuclear shape distribution using the newest approach for the treatment of the fission barrier within the liquid drop model. The present study is the first investigation of the giant dipole resonance width from the fusion-evaporation decay channel in this nuclear mass range.