中子散射相机的探测效率研究

Study on the detection efficiency of a neutron scatter camera

中子散射相机的探测效率直接影响其能量重建的准确性,也是其结构优化最重要的参数之一.在加速器中子源上,采用1.2, 2.5, 3.8, 5.0和14.8 MeV几个能点,对8单元中子散射相机原理系统的探测效率进行了测量.针对实验值比理论值大2～3倍的问题,在理论模拟中加入了碳核发光的影响,并计算了偶然符合事件的影响.计算结果表明,对于单个闪烁体,碳核的发光在高能时不能忽略,而对于散射相机系统,碳核的发光可以忽略.偶然符合对探测效率的影响与入射中子能量有关,对于1.2 MeV中子,偶然符合计数占绝大多数.采用对实验能谱进行高斯拟合扣除了很大一部分的本底中子,将理论探测效率与实验值的偏差缩小到较小的范围内.

The detection efficiency of neutron scatter camera determines the accuracy of its energy reconstruction, which is one of the most important parameters for structure optimization. We measured the detection efficiency of a 8-elements protype of neutron scatter camera with the tandem accelerator in CIAE, using the incident neutron energy of 1.2, 2.5, 3.8, 5.0, 14.8 MeV. To solve the problem of experimental value bigger than the theoretical value by 2-3 times, the luminescence of carbon nucleus was considered in the simulation, and the influence of accidental coincidence was calculated. The results show that although luminescence of carbon nucleus cannot be ignored in high energy for single scintillator, it can be ignored for neutron scatter camera; accidental coincidence has different influence on the detection efficiency for different incident energy. For 1.2 MeV, the accidental coincidence stands for the majority of the events. Using Gauss fitting to the experimental spectra, the background neutrons was taken out, and the deviations between theoretical and experimental values were decreased to an acceptable range.