Measurements of mass and angular distributions of fission fragments from actinide nuclei 249Bk and 257Md, produced in fusion reactions 11B and 19F + 238U, are presented. Experimentally observed mass ratio distributions indicate “multi-chance fission” through the interplay of fission modes in the fission process, and they agree well with predictions from calculations using the GEF (“GEneral description of Fission observables”) model code. Furthermore, to test the signatures of events from non-compound nuclear processes in the fission of 249Bk and 257Md nuclei, Monte Carlo statistical decay model calculations using GEMINI++ were performed for the measured mass distribution at all energies. For comparison purposes, the fission fragment mass distributions of neighboring heavy actinide nuclei, previously measured in the fission of 250Cf and 254Fm nuclei produced by 12C and 16O projectiles on a 238U target, are also presented. The measured angular anisotropy data for the 19F + 238U reaction differ from the results of the Transition State Model (TSM) at energies below the fusion barrier. As a result of the present study, we suggest considering the interplay between K relaxation time, dynamic dissipation, and their influence on shell correction to understand the evolution of fission dynamics in heavy-ion-induced actinide nuclei.

中文翻译：

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重新研究重锕系元素核 249Bk 和 257Md 中裂变模式和非平衡裂变过程的相互作用


介绍了在聚变反应 11B 和 19F + 238U 中产生的锕系元素核 249Bk 和 257Md 裂变片段的质量和角度分布的测量。实验观察到的质量比分布表明，通过裂变过程中裂变模式的相互作用，存在“多机会裂变”，并且它们与使用 GEF（“裂变可观测物的一般描述”）模型代码的计算预测非常吻合。此外，为了测试 249Bk 和 257Md 原子核裂变中非复合核过程事件的特征，使用 GEMINI++ 对所有能量下测量的质量分布进行了蒙特卡罗统计衰变模型计算。为了进行比较，还提出了相邻重锕系元素核的裂变碎片质量分布，之前在 250C 和 254O 弹丸对 238U 目标产生的 16Cf 和 16Fm 原子核的裂变中测量。19F + 238U 反应测得的角度各向异性数据与过渡态模型 （TSM） 在能量低于聚变势垒时的结果不同。作为本研究的结果，我们建议考虑 K 弛豫时间、动态耗散及其对壳层校正的影响之间的相互作用，以了解重离子诱导的锕系元素核中裂变动力学的演变。