快中子能谱在线测量的反冲质子望远镜响应模拟研究

Simulation Study of a Recoil Proton Telescope System Designed for Online Fast Neutron Spectrum Measurement

快中子能谱是基于散裂中子源开展大气中子单粒子效应研究的关键输入参数,在线测量宽能区快中子能谱在近散裂靶位置面临飞行时间法不确定度大、中子通量高、本底干扰强等问题。设计了反冲质子望远镜(RPT)系统,利用Geant4模拟了20~200 MeV中子轰击不同厚度聚乙烯转换靶产生的反冲质子产额、角分布以及能谱,为优化探测系统设计提供了指导依据。通过模拟硅探测器与新型快响应CLLB闪烁体组成的二重符合RPT系统对入射中子的响应,分析了影响探测系统探测效率和能量分辨率的因素,确定了聚乙烯转换靶厚度为1 mm、符合质子探测器摆放角度为26.6°和探测器尺寸等重要参数,得到了RPT系统的中子响应函数矩阵,并计算了其探测效率达10-5,对高中子通量和复杂本底干扰环境下的快中子能谱在线测量具有指导意义和参考价值。

The fast neutron spectrum is a key input parameter for studying atmospheric neutron single event effects(SEE)based on spallation neutron sources.Online measurement of the fast neutron spectrum at the electronics test position near the spallation target faces challenging issues including a large uncertainty with the time-of-flight method,high neutron flux,and strong background interference.A recoil proton telescope(RPT)is suitable in this circumstance but its design and response to fast neutrons should be investigated.The yield of recoil protons,angular distribution,and energy spectrum as a function of the polyethylene thickness have been simulated using Geant4 with incident neutron energy ranging from 20 MeV to 200 MeV.A double coincident RPT system consisting of a thin silicon detector and a thick CLLB scintillator has been designed.Light charged particle identification has been investigated with theΔE-E technique.The detection efficiency and energy resolution have been analyzed considering different target thicknesses and system arrangements.The thickness of the polyethylene target was determined to be 1 mm and the placement angle of the detector was determined to be 26.6°,which was used for online measurement of fast neutron spectrum.The neutron response matrix and the detection efficiency of the RPT system up to 10~(-5)are given.The simulation provides guidance and reference for optimizing the design of an RPT system for online measurement of intense fast neutron spectrum.