发表机构
Advanced Science Research Center, Japan Atomic Energy Agency; Department of Pure and Applied Physics, Kansai University; Joint Institute for Nuclear Research; University of Bordeaux, CNRS, LP2i Bordeaux, UMR 5797（日本原子力机构先进科学研究中心; 关西大学应用物理系; 联合核研究所; 波尔多大学，法国国家科学研究中心，LP2i波尔多）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文用六维Langevin方法分类$^{236}$U裂变模式，通过$k$-means算法识别AS1、AS2和SL模式，发现壳层效应和动能反转，为裂变机制提供新见解。
AI 中文摘要
利用基于Cassini形状参数化的六维Langevin方法研究了热中子诱发$^{235}$U的裂变。通过将$k$-means算法应用于碎片质量和两个碎片的四极形变，将断点事件分类为非对称1（AS1）、非对称2（AS2）和超长（SL）裂变模式。对于每种模式，计算了代表性碎片的质子和中子单粒子能级，以检查其壳层结构。AS1重碎片在$Z=50$和52处表现出质子能隙，在$N=82$和84处表现出中子能隙，而AS2重碎片在$Z=56$和$N=88$处出现充分发展的能隙。AS1和AS2的质量分裂分别接近传统标准I和标准II模式。然而，AS1的平均总动能低于AS2，这与标准I和标准II的传统排序相反。这种反转反映了AS1轻碎片更拉长的形状。SL模式通常用宏观液滴效应来解释，而$Z=46$处显著的质子壳层能隙表明质子壳层效应也对拉长的对称构型有所贡献。基于碎片质量和两个碎片四极形变的分类为区分裂变模式和检查断点处相应碎片壳层结构提供了基础。
英文摘要
Thermal neutron-induced fission of $^{235}$U is studied using a six-dimensional Langevin approach based on the Cassini shape parametrization. Scission events are classified into Asymmetric 1 (AS1), Asymmetric 2 (AS2), and Superlong (SL) fission modes by applying the $k$-means algorithm to the fragment mass and the quadrupole deformations of both fragments. For each mode, proton and neutron single-particle levels are calculated for representative fragments to examine their shell structures. The AS1 heavy fragment exhibits proton gaps at $Z=50$ and 52 and neutron gaps at $N=82$ and 84, whereas well-developed gaps appear at $Z=56$ and $N=88$ in the AS2 heavy fragment. The mass splits of AS1 and AS2 are close to those of the conventional Standard I and Standard II modes, respectively. However, the average total kinetic energy is lower for AS1 than for AS2, opposite to the conventional ordering of Standard I and Standard II. This reversal reflects the more elongated shape of the AS1 light fragment. The SL mode is conventionally interpreted in terms of macroscopic liquid-drop effects, whereas the pronounced proton shell gap at $Z=46$ suggests that proton shell effects also contribute to the elongated symmetric configuration. The classification based on fragment mass and the quadrupole deformations of both fragments provides a basis for distinguishing fission modes and examining the corresponding fragment shell structures at scission.
Comments12 pages, 12 figures, submitted to Physical Review C
