DEFORMATION PATHS OF A NUCLEUS IN FISSION

在^<232>th的质子诱导裂变中，发现了产生A=126 ~ 134裂变碎片的两种动能分量。在本工作中，通过质子能量从12 MeV到16 MeV的变化，研究了^<232>Th和^<238>U的质子诱导裂变中，这两个分量的强度对入射能量的依赖关系。用双TOF法对其动能进行了详细的测量。对飞行时间系统进行了时间校准，使用了来自串联加速器的240 MeV ^<127>I束流。结果清楚地表明，低动能分量的强度与对称分质产物的产率具有相似的入射能依赖性，而高动能分量的强度与非对称分质产物的产率具有相似的入射能依赖性。他们得出结论，在轻锕系元素的低能裂变中确实存在两条变形路径：“一条路径经历了更高的裂变势垒，最终以更细长的分裂构型对称的质量分裂结束，另一条路径经历了更低的裂变势垒，导致更紧凑的分裂构型不对称的质量分裂。”这两种变形路径在裂变中同时存在，产生的碎片质量为126 ~ 134。

Two kinds of kinetic energy components were discovered present for the fission producing fission fragments of A=126-134 in proton induced fission of ^<232>th.In the present work, the incident energy dependence of the intensity of each of those two components was studied for proton-induced fission of ^<232>Th and ^<238>U by varying the proton energy from 12 to 16 MeV.The kinetic energies were carefully measured by the double TOF method. The time calibration of the time-of-flight system was performed using the 240 MeV ^<127>I beam from a tandem accelerator.The results clearly indicated that the intensity of the low kinetic energy component has the incident energy dependence similar to the mass yields of symmetric-mass-division products have while the intensity of high kinetic energy component behaves similarly to the yields of asymmetric-mass-division products.They lead to the conclusion that two deformation paths indeed exist in the low energy fission of light actinide : "one path experiences a higher fission barrier and ends up in symmetric mass division with the more elongated scission configuration, and the other goes over a lower fission barrier and leads to asymmetric mass division with more compact scission configuration.Those two deformation paths co-exist in the fission which produce fragments mass of 126 to 134.