Fission hindrance and nuclear viscosity

Measurements of GDR gamma-rays in coincidence with fission fragments from medium heavy to very heavy systems are drawn. These measurements have shown excess yield of GDR gamma-rays from the fissioning compound nucleus than what is expected from simple transition state model. The excess yield of GDR gamma-rays is explained by incorporating dissipative mechanism through the Kramers formalism in the statistical model calculations. It will be shown, through a systematic analysis of different systems, namely, 16O+208Pb, and 32S+208Pb, over a wide range of excitation energy that the Kramers' viscosity parameter has η no apparent temperature dependence. Instead, it may have some dependence on the angular momentum. The role of various parameters in the modified statistical model analysis, their importance and limitations, will be discussed