同位旋对用裂变截面探测鞍点前摩擦的影响

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

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,σdropf作为激发能的函数。发现^(209)Bi的σdropf要大于^(202)Bi和^(195)Bi的σ_f^(drop),这表明高同位旋系统^(209)Bi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+^(206)Pb和p+^(209)Bi反应的裂变激发函数数据,提取的鞍点前摩擦强度为(3～5)×10^(21)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, σdropf, as a function of excitation energy for three Bi nuclei with different isospins. We find that σdropfbecome larger for209^Bi than for202^ Bi and195^ Bi,indicating a greater sensitivity of fission cross section to friction for high-isospin209^Bi. 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 ＋209^Bi and p ＋208^ Pb reactions, which yield high-isospin210^ Po and 209^Bi systems, and extract a presaddle friction strength of（3-5）×10^21 s^-1 by comparing Langevin simulations with these experimental data.