用于核天体物理实验的活性靶时间投影室

发生在中子星壳层内的丰中子熔合反应对中子星演化以及X射线超级爆等现象均会产生影响。受限于放射性束流强度和反应机制的复杂性，实验数据极其缺乏，难以有效约束理论模型。基于活性靶技术的时间投影室(Time Projection Chamber，TPC)将工作气体作为反应靶，具备近4$\pi$立体角接受度和三维径迹重建能力，能够实现对反应事件的全记录，显著提高了探测效率，大幅降低了熔合反应截面测量对束流强度的要求。我们研制了240路信号读出的TPC，并使用放射性束流16N对探测器进行了测试，探索了该实验方法的可行性和有效性。为了得到更加精确的反应产物径迹，对反应事件做出更好的筛选，进一步发展了1 024路信号读出TPC，并开展了12C+12C库仑位垒附近熔合反应截面测量实验，初步实验结果与已有实验数据符合较好。

Active Target Time Projection Chamber (TPC) for Nuclear Astrophysics Experiments

The fusion reaction of neutron-rich nuclei occurring in the neutron star crust is considered to be the important heating process in neutron stars and X-ray super burst. Limited by the intensity of radioactive beams and the complexity of reaction mechanism, experimental data so far are rare and can not constrain relevant theoretical model effectively. The time projection chamber (TPC) based on the active target technique works with the detection gas as the target, which can record all the tracks including the incident particle and charged particles from the reaction occurring in the detection gas. TPC has approximately 4$\pi$ solid angle acceptance and 3D track reconstruction capabilities, which can significantly improve detection efficiency, making TPC a powerful device to measure the low cross sections of fusion reactions. A 240-channels active target TPC has been developed. The test experiment of 16N+12C fusion measurement was carried out and validated the feasibility of measuring the fusion reaction cross section by active target TPC. In order to obtain more accurate reaction tracks to identify fusion events, a 1024-channels TPC was constructed and then commissioned by measuring the 12C+12C fusion reaction cross section at energies around coulomb barrier. The preliminary result is in good agreement with the existing experimental data.