15C在重靶上的弹性散射研究

At incident energies close to the Coulomb barrier, a typical experimental phenomenon of elastic scattering angular distributions for the weakly bound neutron-rich nuclei, such as 6He, 11Li and 11Be, is observed that the Coulomb rainbow peak is partially or completely suppressed. It has been suggested that this phenomenon is due to both nuclear and Coulomb breakup couplings. However, the experimental data for the energies above the Coulomb barrier is very scarce. The angular distribution of the differential cross section of 8B shows that the Coulomb rainbow peak cannot be suppressed, in contrast to that observed in the elastic scattering at energies around the Coulomb barrier. We plan to measure the elastic scattering cross section of 15C on a 208Pb target at an incident energy of 190MeV, which is equivalent to three times of the nominal Coulomb barrier for 15C+208Pb system, on the Radioactive Ion Beam Line in Lanzhou (RIBLL). Desirable elastic scattering data of 15C will be provided by this experimental measurement. The 15C optical potential can be obtained using the optical model and CDCC（Continuum Discretised Coupled Channels） calculation. The competition between stripping and breakup, and the difference between neutron-halo and proton-halo nuclei in coupled channel effects will be studied. Further studies on the exotic structure of weakly bound nuclei, especially halo nuclei, and the structure effects on the reaction mechanism will also be carried out.

入射能量在库仑位垒附近时，丰中子弱束缚核6He、11Li和11Be等的弹性散射微分截面角分布，表现出库仑虹峰明显压低甚至消失的特征。理论分析表明该现象是由于破裂和转移等直接反应道对弹性散射道有强烈耦合效应的结果。但是较高入射能量下的弹散实验数据比较缺乏，我们完成的3倍位垒能量的质子晕核8B+208Pb弹散实验，其角分布特点和中子晕核不同。本项目拟基于RIBLL装置，充分发挥其次级束流能量较高的优势，精确测量3倍位垒的入射能量190MeV的15C+208Pb弹性散射微分截面角分布，填补单中子晕核15C在此能区弹散实验数据的空白，结合光学模型及耦合道理论分析实验数据，提取15C光学势，研究弹性散射中转移与破裂机制的竞争，中子晕与质子晕在耦合道效应方面的差异，深入探讨弱束缚核尤其晕核的奇特结构及其对核反应机制的影响。

弹性散射过程是研究弱束缚核结构和反应机制的有效手段，尤其是研究弱束缚核表面结构的灵敏探针。基于此前质子晕核8B等弹性散射实验研究的基础上，本项目针对中子晕核15C在重靶上的弹性散射开展实验研究。项目在HIRFL-RIBLL上开展完成了中子晕核15C在Pb靶上的弹散微分截面角分布实验测量，实验结果能够对较高入射能下中子晕和质子晕结构差异对弹性散射反应机制的影响提供深入理解，同时也能研究破裂等直接反应道与弹性散射道之间的强烈耦合效应。项目同时对实验主要探测器PPAC的性能进行了深入研究，取得了重要成果。