Progress of Studies on Reaction Dynamics Induced by Proton Drip-line Nuclei at Energies Around the Coulomb Barrier
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摘要: 质子滴线核在近垒能区的反应机制,尤其是破裂机制,是当前核物理领域的前沿热点问题。为了深入考察质子滴线核的反应动力学,基于日本东京大学的CRIB终端开展了8B+120Sn和17F+58Ni体系在近垒能区的完全运动学测量。本工作在综述前期研究结果的基础上,首次展示了8B+120Sn测量中的熔合截面结果。实验设置方面,针对各自反应体系产物的特点,分别设计了高效率的硅探测器阵列STARE和基于电离室的多层望远镜阵列MITA,实现了反应产物的完全鉴别。对于质子晕核8B+120Sn体系首次实现了破裂碎片的符合测量,重构了完整的破裂过程,揭示了8B出射道瞬时破裂为主的弹性破裂机制。对于质子滴线核17F +58Ni体系则首次实现了全反应道测量,提取了准弹、破裂和总熔合反应的信息,并发现在垒下能区存在熔合截面增强的现象。理论分析表明,这主要是由于破裂连续态的耦合效应所导致,并且8B和17F存在不同的直接反应机制,表明质子晕结构对反应机制存在显著影响。Abstract: Reaction dynamics, especially the breakup mechanisms, induced by proton drip-line nuclei at energies around the Coulomb barrier, is one of the most popular topics in nuclear physics. In order to further investigate the reaction mechanisms of proton drip-line nuclei, we performed the complete-kinematics measurements of 8B+120Sn and 17F+58Ni at CRIB, University of Tokyo. This paper summarizes our research findings and unveils for the first time the fusion cross-section results in the 8B+120Sn measurement. Two detector arrays, i.e., the silicon telescope array of STARE and the ionization chamber array of MITA, were designed respectively for the measurements of 8B and 17F. Reaction products were completely identified with the help of these two arrays. For the 8B+120Sn system, the coincident measurement of the breakup fragments was achieved for the first time. The correlations between the breakup fragments reveal that the prompt breakup occurring on the outgoing trajectory dominates the breakup dynamics of 8B. For 17F+58Ni, the complete reaction channel information, such as quasi-elastic scattering, breakup and total fusion, was derived for the first time. An enhancement of the fusion cross section of 17F+58Ni was observed at the energy below the Coulomb barrier. Theoretical calculations indicate that this phenomenon is mainly due to the coupling to the continuum states. Moreover, different direct reaction dynamics were found in 8B and 17F systems, suggesting the influence of proton-halo structure on the reaction dynamics.
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图 2 8B+120Sn体系在38.7 MeV入射能量下的(a)弹性散射角分布和(b)7Be产物角分布
(a) 中正方形为实验结果,实线和虚线分别为CDCC和单道计算结果;(b) 中星形和菱形分别为符合测量和单举测量得到的7Be角分布;实线为CDCC计算结果。结果取自文献[25]。
图 3 8B+120Sn体系在38.7 MeV入射能量下的(a)相对能量谱和(b)角关联谱
(a) 中实心圆为实验结果,实线和虚线分别为考虑l为0到3以及l = 1的1+共振态的模拟结果;(b) 中实心圆为实验结果,正方形为模拟结果,虚线为1+共振态的模拟结果。结果取自文献[25]。
图 5 MITA探测器阵列
MITA阵列由10个独立单元组成。(a) 每个单元的结构示意图,其包括前端的电离室(IC)以及后续的3层硅探测器,分别由D1,D2和D3表示;(b) 为MITA阵列的实物照片。图片取自文献[29]。
图 6 17F+58Ni体系的角分布结果
空心方形、星形和实心圆分别代表准弹性散射、exclusive和inclusive破裂角分布。细实线、虚线分别为CDCC和不考虑破裂连续态耦合效应(No-CC)的计算结果。粗点划线和虚线分别为CDCC和IAV模型的计算结果,分别对应弹性破裂(EBU)和去弹性破裂(NEB)。两者之和用粗实线表示,对应总破裂(TBU)过程。结果取自文献[26]。
图 7 17F,16O+58Ni体系的熔合反应激发函数
星形和三角形分别表示17F和16O+58Ni的约化熔合截面数据。结果取自文献[26]。实线为理论计算得到的UFF曲线,作为比较的参考标准。
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