基于硼转换的GEM (Gas Electron Multiplier)探测器性能突出，计数率高达10 MHz以上，耐辐射，信号读出方式简单、灵活，位置与时间分辨率高，是下一代中子束流监测器极具优势的候选者。这种新型中子束流监测器主要由硼中子转换层、气体电离粒子放大的GEM以及二维读出电极组成。通过Geant4程序包对探测器物理过程进行蒙特卡罗(Monte Carlo)模拟，主要研究了硼中子转换层转换效率与厚度及中子波长的关系、出射粒子的能谱、不同气体比分不同气体厚度中的能量沉积、以及γ的能量沉积，计算比较了不同厚度GEM膜对快中子产生的影响。模拟结果表明，出射粒子在漂移区的能量沉积几乎与气体比分无关，硼层厚度取0.1μm以下，漂移区厚度6 mm时，可以确保出射粒子在漂移区能量完全沉积，同时具有最佳n/γ区分能力。
The performance of a boron-coated GEM (Gas Electron Multiplier) neutron beam monitor is outstanding, with the counting rate up to 10 MHz, radiation resistance, flexible readout patterns, high resolution in position and time, which is considered as a good candidate for the next generation of neutron beam monitor. This new kind of neutron beam monitor mainly consists of boron convertor, GEM and two-dimensional readout electrode. In this paper, the Monte Carlo simulation on the physical process of the detector has been carried out by using Geant4 package, including the conversion efficiency of the boron layer influenced by the thickness and the neutron wavelength, the spectrum of emitted ions, and the energy deposition of the ions and the gamma in the different gas thickness of several gas volume ratio. Besides, the effect by the fast neutrons with GEM foils has also been calculated. The results show that the ions energy deposited in the drift region is almost independent of the gas volume ratio, the thickness 6 mm of the drift region is adequate for the full energy deposition and the boron thickness smaller than 0.1 μm is the best choice for n/γ separation. This work would be helpful for the detector design and provide an optimized option for the development of the boron-coated GEM neutron beam monitor.
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