Nuclear viscosity of hot rotating ²²⁴Th

In a detailed investigation of giant dipole resonance (GDR) γ-ray yield from the ¹⁶O+²⁰⁸Pb system, the absolute γ-ray/fission multiplicities are extracted and reported over a wide range of excitation energy and angular momentum. The enhanced yield of GDR decay γ rays from the compound system has been analyzed within the framework of a modified statistical model containing the nuclear viscosity as a free parameter. The nuclear viscosity parameter γ has been studied over a much wider range of excitation energy and angular momentum than in earlier works. The measured γ-ray multiplicities as well as known neutron multiplicities and evaporation residue cross sections indicate a strongly damped fission motion. The systematics of the extracted dissipation coefficient is fitted equally well with either temperature or a deformation-dependent nuclear viscosity.