基于次级带电粒子能光系数计算的无机闪烁探测器中子能响研究

The absolute measurement of the pulsed radiation fields is of great importance to the development and operation of nuclear-science devices, material analysis a. However, the pulsed radiation field is usually n/γ mixing fields and the absolute measurement of gamma ray requires knowledge of the detector’s response to neutron. At present, LaBr3:Ce and other inorganic scintillation detectors have been widely used in pulse gamma measurement, but the neutron energy response data are difficult to measure, and have been incomplete. In this project, the second charged particle produced by neutrons in inorganic scintillators is taken as the study object. The objective is to establish a universal and feasible experimental method for measuring the energy-light coefficient of secondary charged particles of inorganic scintillators, which can be used to study the energy response of inorganic scintillators to 0-20 MeV neutrons. Firstly, the energy deposition distribution matrix and fluorescence collection efficiency matrix of various secondary charged particles generated by different energy neutrons in inorganic scintillators with different thickness will be established by Monte Carlo simulation and ray tracing. Then, the fluorescence output equations of secondary charged particles and the energy-light coefficients of secondary charged particles will be calculated, based on white light neutron measurement data. Finally, the calculated results will be corrected by the data of single-energy neutrons and charged particles measurement data.

脉冲辐射场的伽马绝对测量，对大型核科学装置的研制运行、材料分析等都具有重要意义。但脉冲辐射场通常是n/γ混合场，对脉冲伽马的绝对测需要需完整、准确的探测器中子能响数据。目前LaBr3:Ce等无机闪烁探测器虽已广泛用于脉冲伽马测量，但关键的中子能响数据却很难测量，极不完整。本项目以中子在无机闪烁体中产生的次级带电粒子为直接研究对象，建立一种通用可行的、用于测量无机闪烁体次级带电粒子能光系数的实验方法，用以研究无机闪烁体对0-20 MeV中子的能量响应。首先，通过蒙卡模拟和光线追踪建立不同能量中子在不同厚度无机闪烁体中产生的各类次级带电粒子的能量沉积分布矩阵以及对应的荧光收集效率矩阵；然后，结合白光中子测量数据，建立次级带电粒子荧光输出方程组，计算次级带电粒子的能光系数；最后，通过单能中子、带电粒子等数据再对计算结果进行校正。

本项目针对闪烁体对中子的能量响应特性，开展了实验和模拟研究。实验研究方面，建立了一种基于白光中子源的闪烁探测器相对中子能响脉冲测试方法，并基于CSNS白光中子源开展了脉冲辐射场测试常用闪烁体LaBr3:Ce、Yb:YAG、CeF3、ZnO和ST401的相对中子能响研究，首次获得了上述闪烁体对0.5 MeV-20 MeV中子的完整相对能响曲线数据，完善了上述闪烁体在脉冲辐射场测试应用中的关键基础数据；基于北京师范大学串列加速器开展带电粒子响应研究，获得了Yb:YAG、LaBr3:Ce和ST401闪烁体的的质子相对能光曲线。模拟研究方面，通过Geant4模拟ST401闪烁体对中子响应发光及荧光收集的全过程，建立了闪烁体荧光收集系数矩阵，并结合CSNS实验数据计算出了ST401质子相对能光曲线。基于上述研究，建立了一种基于Geant4模拟和白光中子实验的闪烁体中子产生次级带电粒子能光系数研究方法。