超铀新核素238Es的EC缓发裂变研究

EC缓发裂变作为一种奇异的核衰变方式，是研究远离稳定线核素裂变性质的有力工具。通过对EC缓发裂变性质的研究，可以获得原子核的裂变位垒、势能及其演化等信息，对于人们认识原子核的基本性质具有重要的意义。长期以来，受产生截面低、寿命短等因素的制约，远离稳定线核素的EC缓发裂变研究进展缓慢。近些年，分离和探测技术的快速发展，给相关核素的EC缓发裂变研究带来了新的机遇。本项目旨在利用兰州充气反冲谱仪SHANS装置，通过重离子熔合蒸发反应209Bi(32S,3n)238Es，首次合成超铀新核素238Es，研究其EC缓发裂变性质。研究中将首次采用“X射线-裂变碎片”符合测量技术，对238Es的EC缓发裂变过程进行直接指认；首次测量得到238Es的EC缓发裂变概率、EC衰变子核238Cf的裂变碎片质量分布以及平均裂变总动能等信息，检验不同理论模型对远离稳定线核素裂变性质的预言。

As an exotic nuclear decay process, EC-delayed fission (ECDF) is an important tool to study the fission properties of nuclei far from the stability line. Via the study of ECDF, one can obtain the information of fission barrier and nuclear potential-energy landscape, which is crucial to expanding our knowledge of the nucleus. However, the progress on the ECDF study of nuclei far from the stability line is slow for a long time due to their low production rates and short half-lives. In recent years, thanks to the development of separation and detection technology, several new studies are reported and interest in the ECDF has been renewed. In this proposal, the new transuranium isotope 238Es would be synthesized in the fusion evaporation reaction 209Bi(32S,3n)238Es at the gas-filled recoil separator SHANS. The ECDF process will be verified directly by the newly developed X ray-fission coincidence measurement. The delayed fission probability of 238Es and fission mass distributions as well as the mean total kinetic energy of fission fragments would be measured for the first time, which will be compared with different theoretical predictions.