丰质子奇特核17F在铅靶上的破裂实验研究

The breakup reaction of weakly-bound nuclei on heavy targets at intermediate/high energies plays an important role both in the studies of nuclear structure and nuclear reactions of astrophysical interest. The breakup of the weakly-bound proton-rich nuclei has three charged particles in its final state, which makes the mechanism complicated and is not understood enough. The proton drip line nucleus 17F is a typical weakly-bound proton-rich nucleus exhibiting many exotic characteristics. The separation energy of its valence proton is very small. Its first excited state (1/2+) has a proton halo structure. At some international radioactive ion beam facilities physicists have carried out the breakup experiments of 17F on heavy targets, discussing the breakup mechanism and its effects on other channels. However, due to the limit of the experimental data, there are many questions about the contributions from different interactions and the higher-order effects during the breakup process. The 17F beam of 65A MeV provided by the RIBLL terminal of HIRFL accelerator will be used to bombard on a Pb target at Institute of Modern Physics. Two ion telescopes are implemented to perform the measurement of the breakup products 16O and proton. With the invariant mass spectrum of the breakup of 17F, we will study the competition and interference between the nuclear and Coulomb breakup reactions, assess the importance of the E2 transition in the Coulomb excitation, and clarify the contributions from different higher-order effects.

中高能弱束缚奇特核在重靶上的破裂反应在核结构与天体核反应领域扮演着重要的角色。弱束缚丰质子核破裂的末态为三带电体系，机制复杂，仍然没有得到足够充分的认识。质子滴线上的17F是典型的弱束缚丰质子核，具有许多奇特性质，其质子分离能很低，第一激发态（1/2+）具有罕见的质子晕结构。国际上一些放射性核束装置对其破裂反应机制，及其对其它反应类型造成的效应进行了探讨。由于实验数据的局限性，对17F破裂过程中不同相互作用的贡献以及库仑破裂中的高阶效应存在许多疑问。利用近代物理研究所HIRFL加速器RIBLL终端，产生能量为65A MeV的17F次级束轰击Pb靶，使用两组带电离子望远镜同时对破裂产物16O与质子进行测量。通过对17F破裂的不变质量谱分析，研究破裂反应中核力破裂与库仑破裂的竞争与相干，评估库仑激发中E2贡献的重要性，厘清不同高阶效应的贡献。

轻奇特核是指那些远离β稳定线的质量数较小的不稳定核，它们的中子数与质子数相差较多，在核结构存在诸多奇特的性质（例如晕结构与集团结构），相应地在反应动力学机制上也有同稳定核显著不同的特点。开展轻奇特核的核反应实验研究，能够深化对奇特核核反应动力学与核结构的认识。本项目在HIRFL重离子加速器RIBLL终端上进行了26 AMeV的中子晕核15C在C靶上的核反应实验，对实验数据开展处理工作并提取其准弹性散射反应道，获得了15C在12C上的准弹性散射角分布；通过分析角分布获取15C与12C之间的光学势，并结合理论计算与实验数据得到破裂反应的耦合效应。与此同时，开展了关于丰质子奇特核17F与丰中子奇特核6He（及6Li）在C靶上核虹散射机制的理论研究，分别基于“集团折叠模型+光学模型”与“S矩阵方法”对现有数据进行很好地描述，并对不同能量下的理论截面进行了系统性的分析，理论计算指出α与16O这类强束缚核芯对奇特核核虹散射的发生能够起到相当大的作用；同时针对6Li在35 AMeV下的弹性散射数据开展了CDCC计算分析，得出：破裂反应对弹性散射中的核虹既会由于额外吸收的引入而在截面上有所削弱，也会带来耦合效应使得核虹角向大角度移动。这些工作丰富了对轻奇特核的核反应动力学（特别是核虹散射）的机制的认识，为后续开展相关的理论与实验研究提供了参考。