四质子非束缚核^(18)Mg的实验研究  

Experimental Study of the Four-Proton Unbound Nucleus 18Mg

作　　者：金瑜 倪磊 华辉[1] 李智焕[1] 牛晨阳 吴鸿毅[1] JIN Yu;NI Lei;HUA Hui;LI Zhihuan;NIU Chenyang;WU Hongyi(School of Physics and State Key Laboratory of Nuclear Physics and Technology,Peking University,Beijing 100871,China;Institute of Materials,China Academy of Engineering Physics,Mianyang 621907,Sichuan,China)

机构地区：[1]北京大学物理学院和核物理与核技术国家重点实验室,北京100871 [2]中国工程物理研究院材料研究所,四川绵阳621907

出　　处：《原子核物理评论》2024年第1期163-171,共9页Nuclear Physics Review

基　　金：国家重点研发计划项目(2022YFA1602302,2018YFA0404403);国家自然科学基金资助项目(12035001)。

摘　　要：对滴线外原子核自发核子发射现象的实验研究,有助于人们探寻滴线外的新核素,揭示非束缚原子核的奇特结构和衰变特性,进而探索原子核稳定性的极限、理解同位旋极端不对称条件下核子间的相互作用。文章将介绍我们对质子滴线外的新镁同位素^(18)Mg的四质子衰变现象的实验研究。首先介绍实验使用的放射性束流线和探测器设置,给出了束流粒子与衰变产物的粒子鉴别结果。然后重点介绍了闪烁光纤探测阵列及其数据分析方法。结合该阵列在本次实验中的探测效率和位置分辨表现,模拟结果证明了该阵列对于提高不变质量谱分辨的必要性。最后利用不变质量法,由^(14)O+4p五体符合测量事件重建得到了^(18)Mg的衰变能谱。Gamow壳模型理论计算可以较好地描述实验结果,表明连续谱耦合效应对于滴线外原子核的结构存在显著影响。实验测得的^(18)Mg的2_(1)^(+)态激发能比传统幻数核^(20)Mg更高,表明在极端丰质子的Mg同位素中可能出现了N=8的壳减弱或某些奇特的核结构效应。Experimental studies on the spontaneous nucleon emission have enabled the exploration of new isotopes beyond the drip line,as well as revealing their unique structural and decay characteristics.Furthermore,such studies are of critical importance for exploring the limits of nuclear stability and understanding the nucleon-nucleon interactions under extreme conditions of isospin asymmetry.This paper introduces our experimental study on the four-proton decay of ^(18)Mg,a new magnesium isotope beyond the proton drip line.Firstly the radioactive nuclear beamline and detector appratus are introduced,and the results of the particle identification of beam particles and decay fragments are presented.Then the scintillating fiber array is mainly introduced together with its data analysis method.With its performance of detection efficiency and position resolution,this array has been proven by simulation to be very necessary for improving the energy resolution of the invariant mass spectrum.Finally,with the five-body coincidence measurement of ^(14)O+4p,the decay energy spectrum of ^(18)Mg was constructed using the invariarit mass method.The experimental results can be relatively well described by the Gamow Shell Model,demonstrating the significant impact of continuum coupling effect on the structure of nuclei beyond the drip line.The measured 2t excitation energy in ^(18)Mg is higher than that in the traditional magic nucleus ^(20)Mg,which suggests that a possible demise of the N=8 shell closure or some exotic nuclear structure effect may occur in this extremely proton-rich Mg isotope.

关 键 词：滴线 新核素 四质子衰变 ^(18)Mg 不变质量法 N=8壳 

分 类 号：O571.53[理学—粒子物理与原子核物理]