Excitation energy and nuclear dissipation probed with evaporation-residue cross sections

Using a Langevin equation coupled with a statistical decay model, we calculate the excess of evaporation-residue cross sections over its standard statistical-model value as a function of nuclear dissipation strength for Hg-200 compound nuclei (CNs) under two distinct types of initial conditions for populated CNs: (i) high excitation energy but low angular momentum (produced via proton-induced spallation reactions at GeV energies and via peripheral heavy-ion collisions at relativistic energies) and (ii) high angular momentum but low excitation energy (produced through fusion mechanisms). We find that the conditions of case (ii) not only amplify the effect of dissipation on the evaporation residues, but also substantially increase the sensitivity of this excess to nuclear dissipation. These results suggest that, in experiments, to obtain accurate information of presaddle nuclear dissipation strength by measuring evaporation-residue cross sections, it is best to choose the heavy-ion-induced fusion reaction approach to yield excited compound nuclei.