双中子晕核14Be的软偶极激发研究

Different from stable nuclei, strong low-lying Coulomb excitation (dominantly E1) near the neutron threshold is observed in the peripheral collisions of neutron-halo nuclei on heavy nuclei. Such exotic excitation of halo nuclei probes nuclear properties such as the size, the shape, the distribution of neutrons and protons as well as the in-medium nucleon-nucleon interaction. This project will utilize the 14Be beam of 35AMeV to projectile on Pb target to obtain the soft dipole excitation on the RIBLL terminal of HIRFL-CSR at Institute of Modern Physics in Lanzhou. By a kinematicallly complete measurement of incident beam and outgoing particles, all their momentum vectors are obtained to give the excitation spectrum of 14Be. Through the experimental run without target and of C target the background and nuclear excitation contributing to the excitation of 14Be is eliminated respectively. With the residual electromagnetic excitation cross section in cooperate with scattering angle of 14Be on Pb the excitation B(E1) is constructed. The integration of B(E1) is used to analyze the size of 14Be and the double-halo-neutron correlation. Furthermore, introducing the structural information of the 12Be core of 14Be, a 12Be+n+n three-body model is implemented to extract the wave function of the halo neutrons in 14Be.

中子晕核与重核的外围碰撞过程中，在中子分离阈能附近观察到很强的库仑激发强度（主要是E1）。通过对中子晕核该奇特性质的研究可以获得原子核的尺寸、形状、中子和质子的空间分布以及在核物质背景下核子-核子特殊相互作用机制的信息。本项目拟在兰州近代物理研究所的HIRFL-CSR装置的RIBLL终端上，通过35AMeV的14Be束在Pb靶上的非弹散射实现双中子晕核14Be的软偶极激发。通过对入射核束和出射产物12Be+n+n的动力学全测量，测量各动量矢量，以此来获得14Be的激发能谱。通过无靶和C靶实验扣除本底及14Be+Pb中的核激发成分获得以E1为主的电磁激发截面，结合14Be在Pb上的散射角重构B(E1)。通过B（E1）积分强度分析14Be的尺寸和晕中子的双中子关联程度。进而，尝试在14Be的核芯12Be中引入结构信息，利用12Be+n+n的三体模型来研究14Be晕中子波函数的组态信息。

通过中子晕核的奇特性质研究，可以获得原子核的尺寸、形状、中子和质子的空间分布以及在核物质背景下核子—核子特殊相互作用机制的信息。本项目在HIRFL重离子加速器RIBLL终端上进行了35MeV/u的17C+12C的实验。17C在碳靶上主要有弹性散射、破碎（有单中子、双中子和三中子移去等）等反应方式。通过对17C弹散截面的研究获得其核反应的光学势，为进一步的集团结构等物理研究提供依据；结合理论计算和现有数据进行系统性研究，获得其光学势对能量的依赖性及其与破碎道的耦合性质。与此同时，建立了核物理实验的模拟平台，并通过中子、伽马等探测的模拟和相关实验测试对其可行性进行了验证，进行了14Be破碎实验设置（靶厚、探测器性能）对实验结果的影响进行了研究。