Effects of isospin and shell on probing nuclear dissipation with survival probabilities of heavy systems

Abstract

Using the Langevin model, we calculate the survival probability (Peva) of 228U, 234U and 240U as a function of the presaddle dissipation strength (β). It is shown that Peva displays a greater sensitivity to β with increasing the isospin of the U system and with decreasing excitation energy and angular momentum, and that shell effects can significantly enhance the sensitivity. Furthermore, we compare calculated and measured evaporation residue cross sections of heavy compound nuclei 224Th produced in the 16O + 208Pb reaction and find that the best-fit value of β required to satisfactorily describe the measured data has an apparent drop as shell effects are taken into account in the calculation compared to that neglecting the effects, clearly indicating a strong influence of shell effects on the precise determination of β. These results demonstrate that to more stringently constrain the strength of presaddle dissipation with survival probabilities of heavy nuclei, on the experimental side, it is best to produce high-isospin compound systems with low energy and low spin; theoretically, it is important to account for the shell effects in the calculations.