Significant role of level-density parameters in probing nuclear dissipation with light-ion-induced fission excitation functions

We study the influence of the ratio of level-density parameters at saddle to that at ground-state configuration (${a}_{f}$/${a}_{n}$) on the sensitivity of fission cross sections (${\ensuremath{\sigma}}_{\mathrm{fiss}}$) to presaddle dissipation effects by comparing fission excitation functions measured in the ${}^{3}$He + ${}^{197}$Au (${}^{208}$Pb) reactions with three distinct types of model calculations: the standard Bohr-Wheeler theory with ${a}_{f}$/${a}_{n}$ $=$ 1 (i) and ${a}_{f}$/${a}_{n}$ $\ensuremath{\ne}$ 1 (ii) as well as the Langevin approach with ${a}_{f}$/${a}_{n}$ $\ensuremath{\ne}$ 1 (iii). It is shown that both cases (i) and (ii) cannot provide a reasonable, satisfactory description of the measured ${\ensuremath{\sigma}}_{\mathrm{fiss}}$. A presaddle friction strength ($\ensuremath{\beta}$) of (4--4.5) $\ifmmode\times\else\texttimes\fi{}$ 10${}^{21}$ s${}^{\ensuremath{-}1}$ is extracted through reproducing data with Langevin simulations. We find from the comparison of the experimental and calculated ${\ensuremath{\sigma}}_{\mathrm{fiss}}$ in cases (ii) and (iii) that a precise determination of $\ensuremath{\beta}$ depends sensitively on ${a}_{f}$/${a}_{n}$. The finding indicates that level-density parameters play a significant role in accurately probing presaddle friction; that is, to stringently constrain $\ensuremath{\beta}$ it is important to take into account a realistic and an elaborate evaluation of ${a}_{f}$/${a}_{n}$ in theoretical calculations. We further find that high energy increases the sensitivity of ${\ensuremath{\sigma}}_{\mathrm{fiss}}$ to $\ensuremath{\beta}$, suggesting that in experiments, to obtain precise information of presaddle dissipation by measuring ${\ensuremath{\sigma}}_{\mathrm{fiss}}$, it is best to populate a compound nucleus with high energy.