Influence of Isospin on Fission Cross Section as a Probe of Presaddle Nuclear Dissipation

Langevin models that are coupled with particle emission are applied to calculate the drop of fission cross section caused by friction over its standard statistical-model value, σ_f^drop, as a function of excitation energy for three Bi nuclei with different isospins. We find that σ_f^drop become larger for ²⁰⁹Bi than for ²⁰²Bi and ¹⁹⁵Bi, indicating a greater sensitivity of fission cross section to friction for high-isospin ²⁰⁹Bi. These results suggest that, to more accurately determine the presaddle dissipation strength by measuring fission excitation functions, it is best to populate those compound systems with a high isospin. Furthermore, we analyze the data of fission excitation functions measured in p + ²⁰⁹Bi and p + ²⁰⁸Pb reactions, which yield high-isospin ²¹⁰Po and ²⁰⁹Bi systems, and extract a presaddle friction strength of (3-5)×10²¹ s^-1 by comparing Langevin simulations with these experimental data.