摘要: 耦合了轻粒子发射的随机Langevin模型被用于计算三个Bi裂变系统因核耗散效应引起的相对于标准统计模型预计的裂变截面值的变化，σ_f^drop作为激发能的函数。发现²⁰⁹Bi的σ_f^drop要大于²⁰²Bi和¹⁹⁵Bi的σ_f^drop，这表明高同位旋系统²⁰⁹Bi的裂变截面对摩擦强度有更大的敏感性。该结果建议，当实验上使用裂变激发函数来更精确地提取鞍点前摩擦强度时，应产生具有高同位旋的复合核。进而，通过Langevin计算拟合p+²⁰⁶Pb和p+²⁰⁹Bi反应的裂变激发函数数据，提取的鞍点前摩擦强度为（3~5）×10²¹ s^-1。


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.