弱束缚原子核引起的熔合反应机制研究

弱束缚原子核引起的熔合反应机制研究是近几十年中实验核物理研究的重要课题之一。相比于放射性核束，加速器提供的稳定弱束缚原子核束流的强度要高几个数量级，利用稳定弱束缚原子核作为弹核进行反应机制的研究，可以在保证统计性和准确性的基础上，深入研究原子核的破裂、转移等反应道对熔合过程的耦合作用。已有很多实验数据表明，在库仑位垒附近，弱束缚原子核引发的熔合反应有很多有趣的现象，例如完全熔合截面的“垒下增强”和“垒上压低”。本文主要回顾近年来弱束缚原子核“垒上压低”的研究结果，并探讨造成“垒上压低”的可能原因。完全熔合截面“垒上压低”的主要原因是弱束缚原子核在进入熔合位垒之前发生破裂，从而降低了完全熔合反应道的入射通量。同时，实验研究表明完全熔合截面压低的程度可能与靶核质量数以及靶核结构相关。目前，在实验上对弱束缚原子核引起的熔合反应研究主要有3种测量方法，分别为$gamma$射线测量方法、带电粒子测量方法以及带电粒子-$gamma$射线符合测量的方法。其中，带电粒子-$gamma$射线符合测量的方法在反应道鉴别方面具有明显的优势。本文对这3种测量方法进行了概要介绍，并就国内外对运用这3种方法开展的研究进行了介绍，包括本研究组在此方面的研究工作。此外，对弱束缚原子核引起的熔合反应近期在理论方面的研究工作也做了些介绍。

Study of Fusion Reaction Mechanism Induced by Weakly Bound Nuclei

Investigation of fusion reaction mechanism is one of important topics in recent years. In comparison with radioactive ion beam, the beam intensities of weakly bound nuclei are orders of magnitude higher. The study of the reaction mechanism induced weakly bound nuclei can further explore the coupling effect of breakup, transfer and other reaction channels on the fusion process. A lot of experimental data have shown that there are many interesting phenomena in the fusion reaction induced by weakly bound nuclei at energies near the Coulomb barrier, such as "enhancement below the Coulomb barrier' and "suppression above the Coulomb barrier' of the complete fusion cross section. In this paper, we mainly review the researches of the suppression phenomenon and discuss the possible reasons for the suppression. The main reason for the suppression phenomenon of the complete fusion cross section is that the weakly bound nuclei break up before entering the fusion barrier, thus reducing the incident flux of the complete fusion reaction channel. At the same time, the experimental results show that the degree of suppression may be related to the mass number and structure of target nuclei. There are three kinds of methods to measure the fusion reaction induced by weakly bound nuclei, which are $gamma$ ray measurement, charged particle measurement and charged particle -$gamma$ ray coincidence measurement. The charged particle -$gamma$ ray coincidence measurement has obvious advantages in reaction channel identification. This paper introduces the three measurement methods and the researches using these three methods at home and abroad, including the researches of our groups. In addition, the recent theoretical research work on fusion reactions induced by weakly bound nuclei is also introduced.