基于微观输入的裂变建模：中子诱导反应的激发能量依赖裂变路径

中文摘要 AI 辅助

为了计算透射系数，当前的Hauser-Feshbach反应代码假设裂变路径是一维的，且该路径既独立于激发能量，又普遍适用于不同的裂变通道。相比之下，微观裂变研究通常探索多个集体变量。因此，基于微观输入预测可观测裂变量（如截面）需要一种方法来降低后者的维度。对于自发裂变，最小作用量路径（LAP）——它使半经典作用量最小化并使透射系数最大化——是解决方案。我们证明LAP不能推广到其他裂变模式，如中子诱导裂变或β延迟裂变：在有限激发能量下，LAP通常不能使透射最大化。微观势能面（PES）可能存在多个共存的驻定作用量路径。我们表明这些路径（i）可以随激发能量改变其作用量排序，并且（ii）产生不同的中子诱导裂变截面预测，但同样能很好地匹配已知的自发裂变寿命。对于BSkG3 Skyrme型能量密度泛函模型，从零激发能量下的轴对称LAP过渡到利用三轴自由度的路径，其发生时的激发能量对于几乎所有锕系元素和大多数未知奇异核而言都小于中子分离能。

英文摘要

To calculate transmission coefficients, current Hauser-Feshbach reaction codes assume a one-dimensional fission path that is both independent of excitation energy and universal across different fission channels. In contrast, microscopic fission studies typically explore multiple collective variables. Predicting observable fission quantities such as cross sections based on microscopic input thus requires a way to reduce the dimensionality of the latter. For spontaneous fission, the least action path (LAP) -- which minimizes the semiclassical action and maximizes the transmission coefficient -- is the solution. We demonstrate that the LAP does not generalize to other fission modes such as neutron-induced or $β$-delayed fission: at finite excitation energy, the LAP generally does not maximize the transmission. A microscopic PES can have multiple coexisting stationary-action paths. We show that these (i) can switch their action ordering as a function of excitation energy and (ii) yield different neutron-induced fission cross sections predictions, yet match known spontaneous fission lifetimes equally well. For the BSkG3 Skyrme-type energy density functional model, the transition from the axially symmetric LAP at zero excitation energy to a path exploiting the triaxial degree of freedom occurs at an excitation energy that is smaller than the neutron separation energy for essentially all actinides and the majority of unknown exotic nuclei.

发表机构

• Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles（布鲁塞尔天文与天体物理研究所，布鲁塞尔自由大学）
• Brussels Laboratory of the Universe - BLU-ULB（宇宙布鲁塞尔实验室）

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