位垒附近团簇结构对轻核系统融合反应影响的实验研究

Theoretical and experimental interest is rapidly growing in fusion reaction by which weakly bound nucleus or halo nuclei induced near Coulomb barrier. In light systems, cluster structure and halo structure becomes significant because the Coulomb contribution becomes small. However, experimental studies for the fusion reaction between light systems are very rare. Moreover, the existing data are inconsistent between those in which different techniques were used, either dE-SiE telescopes or characteristic gamma ray measurements. Therefore, in order to investigate the cluster structure effect on fusion reaction, we propose a new detective technique to measure 6Li+ 13C,7Li+12C fusion reaction cross section. we plan to set up a high efficiency detector system, which consists of a time projection chamber type-ion chamber(TPC-IC),employed with gas electron multiplier(GEM) and Flash ADC, to obtain good quality data. Meanwhile, theoretical calculations using an antisymmetrized molecular dynamics model（AMD） and a statistical decay code, Gemini, will be performed. By comparing the calculated results with experimental data, we can investigate the effect of cluster structure, as well as projectile break up effect and incomplete fusion dynamic aspects on fusion reaction. This project can also shed light on future study on the cluster structures of the exotic nuclei such as 8B or 11,12B.

库仑位垒附近弱束缚核与晕核引起的融合反应在理论上和实验上引起了日趋广泛地关注。但轻系统融合反应中，库仑贡献减小使得团簇结构和晕结构变得更显著，但实验研究较少，而且利用气体望远镜dE-SiE和gamma特征谱测得的实验数据不一致。为此，我们提出利用新的探测技术来测量6Li+ 13C,7Li+12C的融合反应截面，以研究团簇结构对融合的影响。我们计划建立时间投影电离室（TPC-IC），联合气体倍增器（GEM）和Flash ADC一套高探测效率装置来获取高质量实验数据。同时，我们将在理论上用反对称化分子动力学模型（AMD）和统计衰变程序Gemini来进行模拟计算，并与实验数据相比较，由此来探讨融合反应中的团簇结构效应及其引起的弹核碎裂效应、部分融合等动力学方面的影响。本项目的结果将为进一步研究奇异核团簇结构（如8B或11，12B）奠定基础。

库仑位垒附近轻弱束缚核团簇结构对总融合反应截面有着显著的影响。理论上利用分子动力学AMD模型与统计模型GEMINI模拟了质心系下入射能Ec.m.=3-8 MeV，碰撞参数b=0-7fm的融合反应7Li + 12C和6Li + 13C。 AMD预测了基态下7Li具有两个非常形变的团簇结构: d + d + t和t + α结构，而6Li具有两个不同的团簇结构: d + α和d + d + d结构。6Li (d, α)的核半径比6Li (d, d, d)小，结合能也低, 因此前者的融合截面要比后者小，同理7Li (d, t, d)也比7Li (t, α)融合截面小。7Li + 12C核反应中，完全融合反应形成的19F和部分融合反应形成的15N+α为主要出射道，而完全融合反应在低入射能时占80%的几率，而在高入射能时下降到了70%。实验上，组建了时间投影电离室TPC-IC探测器并优化了测试条件。利用铁源在Ar/CO2和C4H10/CO2工作气体中，分别对TPC-IC探测器中的GEM膜和漂移室进行了测试，得到Ar/CO2在三层GEM膜的增益为10^4，而C4H10/CO2在三层GEM膜的增益为7×10^4。另外还利用了兰州重离子加速器冷却储存环（CSR）及兰州第二条放射性束流线（RIBLL2，产生了能量约为160MeV/n，流强为105~106PPS的高能放射性束流12C，对GEM探测器和TPC性能进行了初步测试, 为轻核系统融合反应的物理实验探索提供实验经验和依据。