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Mass-energy distribution of fragments within Langevin dynamics of fission induced by heavy ions

机译：重离子引起的裂变动力学中朗芬蛋白内碎片的质量能分布

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摘要

A stochastic approach based on four-dimensional Langevin fission dynamics is applied to calculating mass-energy distributions of fragments originating from the fission of excited compound nuclei. In the model under investigation, the coordinate K representing the projection of the total angular momentum onto the symmetry axis of the nucleus is taken into account in addition to three collective shape coordinates introduced on the basis of the {c, h, α} parametrization. The evolution of the orientation degree of freedom (K mode) is described by means of the Langevin equation in the overdamped regime. The tensor of friction is calculated under the assumption of the reducedmechanismof one-body dissipation in the wall-plus-window model. The calculations are performed for two values of the coefficient that takes into account the reduction of the contribution from the wall formula: k _s = 0.25 and k _s = 1.0. Calculations with a modified wall-plus-window formula are also performed, and the quantity measuring the degree to which the single-particle motion of nucleons within the nuclear system being considered is chaotic is used for k _s in this calculation. Fusion-fission reactions leading to the production of compound nuclei are considered for values of the parameter Z ~2/A in the range between 21 and 44. So wide a range is chosen in order to perform a comparative analysis not only for heavy but also for light compound nuclei in the vicinity of the Businaro-Gallone point. For all of the reactions considered in the present study, the calculations performed within four-dimensional Langevin dynamics faithfully reproduce mass-energy and mass distributions obtained experimentally. The inclusion of the K mode in the Langevin equation leads to an increase in the variances of mass and energy distributions in relation to what one obtains from three-dimensional Langevin calculations. The results of the calculations where one associates k s with the measure of chaoticity in the single-particle motion of nucleons within the nuclear system under study are in good agreement for variances of mass distributions. The results of calculations for the correlations between the prescission neutron multiplicity and the fission-fragment mass, 〈n _(pre)(M)〉, and between, this multiplicity and the kinetic energy of fission fragments, 〈n _(pre)(E _k)〉, are also presented.
机译：基于四维兰格文裂变动力学的一种随机方法被用于计算源自受激复合核裂变的碎片的质量能分布。在所研究的模型中，除了基于{c，h，α}参数化引入的三个集合形状坐标外，还考虑了代表总角动量在核对称轴上的投影的坐标K。取向自由度（K模式）的演化通过过阻尼状态下的Langevin方程描述。摩擦张量是在壁加窗模型中假设单体耗散的机制降低的情况下计算的。针对考虑到墙公式的贡献减少的两个系数值执行计算：k _s = 0.25和k ss = 1.0。还执行了具有修改后的“壁加窗”公式的计算，并且在此计算中，将测量所考虑的核系统内核子的单粒子运动的混沌程度的量用于k s。对于参数Z〜2 / A的值，在21至44之间的范围内，考虑了导致化合物核生成的裂变反应。选择如此宽的范围以便不仅对重原子而且还对重原子进行比较分析。在Businaro-Gallone点附近的轻化合物核。对于本研究中考虑的所有反应，在四维Langevin动力学内进行的计算均忠实地再现了通过实验获得的质量能和质量分布。 Langevin方程中包含K模式会导致质量和能量分布的方差相对于从三维Langevin计算中获得的结果有所增加。在将k s与所研究的核系统内核子的单粒子运动中的混沌度相关联的计算结果与质量分布的变化非常吻合。分裂中子多重性与裂变碎片质量〈n _（pre）（M）〉之间的相关性以及该多重性与裂变碎片动能〈n _（pre）（ E_k）〉，也被提出。

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