轻丰中子核的奇特结构研究进展  

Progress of exotic structure studies in light neutron-rich nuclei

作　　者：楼建玲[1,2] 叶沿林[1,2] 杨再宏 李奇特[1,2] 许金艳 Jianling Lou;Yanlin Ye;Zaihong Yang;Qite Li;Jinyan Xu(Depariment of Technical Physics,School of Plysics,Peking Universiy,Beijing 100871,China;Slate Key Laboratory of Nuclear Physics and Technology,School of Physics,Peking University Bejing 100871,China)

机构地区：[1]北京大学物理学院技术物理系,北京100871 [2]北京大学物理学院核物理与核技术国家重点实验室,北京100871

出　　处：《科学通报》2023年第9期1004-1015,共12页Chinese Science Bulletin

基　　金：国家重点研发计划(2018YFA0404403);国家自然科学基金(12275007,11775004,U1867214,11875074,11961141003);核物理与核技术国家重点实验室自主科研(NPT2021ZZ01)资助。

摘　　要：不稳定核的奇特结构,例如集团结构、闯入态等,是放射性核束物理研究的热点方向之一.直接核反应实验是研究丰中子核奇特结构的重要手段之一.本课题组自主研发了适用于放射性束流在质子和氘靶上发生直接核反应实验研究的带电粒子探测阵列.利用该高精度、大立体角、模块化、多用途的探测阵列,我们在轻丰中子核的奇特结构实验研究方面取得了一系列重要进展:从实验上确认了^(14)C的π型线性链状分子转动带;发现了丰中子核^(16)C的π2σ2构型线性链状分子结构,^(14)C的一个共振态可能有“3α呈线性排列”的线链超形变结构.我们定量研究了^(12)Be、^(13)B等N=8附近丰中子核的s波和d波闯入强度,结果表明:^(12)Be基态中s波占19%,远远小于^(11)Be(~80%),而d波成分却高达57%,是主要的闯入成分;^(13)B基态中的s(d)波闯入成分约为12%(5%),处于从Be到C的过渡.In order to study the exotic structures in unstable nuclei,including cluster structures and intruder states,we develop a silicon detection array,which is suitable for the direct nuclear reactions induced by radioactive beams on the proton and deuteron targets.We outline the Q-value resolution deduced from the invariant-mass method(IM)and the missing-mass method(MM),the extraction of excitation energy(Ex),spin-parity(J^(π)),and spectroscopic factors,as well as experimental evidences of cluster structures.We present the latest experimental results about the linear-chain molecular bands in the neutron-rich nuclei ^(14)C and ^(16)C,and the intruder s-and d-wave strengths in the neutron-rich N=8 nuclei.First ofall from a clustertransfer experiment ^(9)Be(^(9)Be,^(14)C*→α+^(10)Be)^(4)He,we found that a state at 22.5(I)MeVin'C decays predominantly into the states around 6 MeV in ^(10)Be daughter nucleus,in line with the unique property of the predicted band head of the o-bond linear-chain molecular states.Moreover,a radioactive beam C was excited to the highlying excited states(above the cluster separation threshold)by the inelastic scattering of deuterons.For the first time,we deduced good resolution Q-value spectra using the three-fold events of ^(4)He+^(12)Be+d and ^(6)He+^(10)Be+d,which alow the reconstruction of the ^(14)C excitation spectra according to their decay paths.The close-threshold resonance at 16.5 MeV is assigned as the J^(π)=0^(+) band head of the predicted positive-parity linear-chain molecular band with(3/2_(π)^(-))(1/2_(σ)^(-))^(2) configuration,according to the associated angular correlation and decay analysis.Other members of this band were found at 17.3(2^(+)),19.4(4^(+)),and 21.6(6^(+))MeV based on their selective decay properties,being consistent with the theoretical predictions.Furthermore,a new proton inelastic excitation and cluster-decay experiment for ^(14)C was performed.Similar to the ^(16)C experiment stated above,all three final particles were detected in coincidence,allowing cl

关 键 词：直接核反应 集团结构 闯入态 不变质量 缺失质量 

分 类 号：O571[理学—粒子物理与原子核物理]