涂硼GEM中子束流监测器物理过程的蒙特卡罗模拟

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。     

位敏型探测器数字法读出研究(英文)

中国散裂中子源( CSNS ) 的建造对中子探测器提出了非常高的要求,如更大的有效面积、二维位置灵敏、高计数率、高探测效率和低的 灵敏度等。与传统的模拟读出方法相比,数字法读出具有更高的计数率, 更小的数据传输量,更简单的电子学设计以及更高的信噪比。对数字法读出进行了理论计算,利用GEM探测器的原始数据分析了数字法读出的位置分辨率与读出条宽度的关系。结果表明,数字法读出对于位置分辨要求较低( 小于4 mm) 的大面积位置灵敏探测器是一种较好的选择,如CSNS 小角谱仪探测器。Efficient thermal neutron detectors with large area, two-dimensional position sensitive, high counting rate high detection efficiency and low gamma sensitivity are required to satisfy the demands for the China Spallation Neutron Source (CSNS). Compared with the traditional analog readout method, the digital readout method has the advantages of higher counting rate, smaller quantity of data transmission, simpler readout system and higher signal to noise ratio. The theoretical analysis of the digital readout method is reported in this paper. Used the raw data of GEM detector, the relationship between the position resolution and the width of the readout strip was studied. The results indicate that the digital readout method could be a good choice for the large area position sensitive detector where the requirement of position resolution is less than 4 mm, e.g. the detector of Small-Angle Neutron Scattering (SANS) diffractometer of CSNS.     

应用于热中子的nTHGEM探测器性能研究

随着脉冲强流中子源的发展,对高性能中子探测器提出了更大的挑战,3He气体资源严重短缺和高计数率中子探测器的迫切需求,已开始制约着中子源应用技术的发展。中国科学院高能物理研究所针对中子的特殊性,专门研发了一种陶瓷基材的nTHGEM（neutron Thick Gaseous Electron Multiplier）探测器用于中子探测。基于nTHGEM的中子探测器具有高计数率、高位置与时间分辨能力、增益大、制作工艺简单,且便于大面积制作的特点,是目前国际上发展替代3He探测技术的重要方向之一。为了详细研究nTHGEM探测器的本身性能,本工作使用55Fe放射源研究了nTHGEM探测器的增益、计数率稳定性、能量分辨率等关键参数与nTHGEM膜间电压、收集场强、漂移场强之间的关系,优化了nTHGEM探测器在不同工作气体中的工作参数,为后续进一步优化nTHGEM探测器设计和工艺奠定了基础。实验结果表明,单层nTHGEM探测器在Ar（90%）+CO₂（10%）混合气体中增益能达到103,探测器计数率稳定性良好。另外,还在中国原子能科学研究院的CARR反应堆（China Advanced Research Reactor）上进行了中子束流实验,通过狭缝测量到探测器位置分辨率为（3.01±0.03）mm（FWHM）,已经接近高气压3He MWPC中子探测器水平。With the development of pulsed intense neutron source, the high-performance neutron detector poses more challenges. The severe shortage of 3He gas resources and the urgent need of neutron detector with high counting rate have begun to restrict the neutron source application technology development. In response to the particularity of neutrons, the Institute of High Energy Physics of CAS developed a nTHGEM(neutron Thick Gaseous Electron Multiplier)of ceramic substrate for neutron detection. The neutron detector based on nTHGEM is one of the most important directions for the development of alternative 3He detection technology in the world at present because of its high counting rate, high position and time resolution, large gain, simple fabrication process and large area production. In order to study the properties of nTHGEM detector in detail, this paper studied the relationship between nTHGEM detector's gain, counting rate stability, energy resolution and other key parameters and nTHGEM film voltage, collection field strength and drift field strength using 55Fe radioactive source, Optimized the working parameters of nTHGEM detector in different working gases, which laid the foundation for further optimization of nTHGEM detector design and process. The experimental results show that the single-layer nTHGEM detector has a gain of 103 in a Ar(90%)+CO₂(10%) mixed gas with good counting rate stability. In addition, a neutron beam experiment was performed on the China Advanced Research Reactor at the China Institute of Atomic Energy, and the position resolution of the detector was (3.01±0.03) mm (FWHM) measured by slits. Its performance is close to the high pressure 3He MWPC neutron detector level.     

基于阻性阳极读出方法的气体电子倍增器二维成像性能

新型微结构气体探测器,如气体电子倍增器(gas electron multiplier,GEM)等,具有非常好的位置分辨率潜力(σ100μm),但是需要匹配大规模高密度的读出电子学,给探测器的建设、造价、功耗、空间利用等带来极大压力.阻性阳极读出方法可以在保持较高位置分辨率的前提下,大幅节省电子学.基于厚膜电阻工艺,一种新的阻性单元阵列结构被成功开发和应用于三级级联GEM探测器的读出阳极.该阻性阳极包括6×6个6 mm×6 mm的基本阻性单元,仅需匹配49路读出电子学.~(55)Fe放射源(5.9 keV)和X光机(8 keV)实验的结果显示探测器的位置分辨率(σ)可好于80μm,位置非线性好于1.5%.同时,探测器还获得了很好的实物成像效果.探测器的优良性能表明这种阻性阳极读出方法适用于大面积二维成像气体探测器的读出,并可用于其他探测器的读出.     

Study of a nTHGEM-based thermal neutron detector

With new generation neutron sources, traditional neutron detectors cannot satisfy the demands of the applications, especially under high flux. Furthermore, facing the global crisis in ~3He gas supply, research on new types of neutron detector as an alternative to ~3He is a research hotspot in the field of particle detection. GEM(Gaseous Electron Multiplier) neutron detectors have high counting rate, good spatial and time resolution, and could be one future direction of the development of neutron detectors. In this paper, the physical process of neutron detection is simulated with Geant 4 code, studying the relations between thermal conversion efficiency, boron thickness and number of boron layers. Due to the special characteristics of neutron detection, we have developed a novel type of special ceramic n THGEM(neutron THick GEM) for neutron detection. The performance of the n THGEM working in different Ar/CO_2 mixtures is presented, including measurements of the gain and the count rate plateau using a copper target X-ray source. A detector with a single n THGEM has been tested for 2-D imaging using a ~(252)Cf neutron source. The key parameters of the performance of the n THGEM detector have been obtained, providing necessary experimental data as a reference for further research on this detector.     

CEE-TPC中GEM读出探测器传输性能实验研究

气体电子倍增器(GEM)因其具有较好的位置分辨以及各项同性的二维结构等优点，近年来受到了广泛的关注，在HIRFL-CSR上正在建设的低温高密核物质测量谱仪(CEE)也计划使用GEM作为TPC的读出探测器。不同电场条件下GEM探测器的传输特性对探测器的有效增益及能量分辨有较大影响。文中研究了单层GEM探测器中漂移区电场及感应区电场对探测器传输特性的影响；随后研究了双层GEM探测器的电压分配及传输区电场对探测器电荷传输性能的影响。结果表明，在单层及多层GEM探测器中，漂移区电场、传输区电场及感应区电场主要通过改变电子透过率和GEM雪崩电场强度及分布影响探测器的电荷传输性能，进而影响探测器的有效增益及能量分辨。以上实验结果表明GEM探测器是CEE-TPC读出探测器的理想选择，同时测试结果也为TPC中多层级联GEM工作点的选择提供了参考依据。     

Monte Carlo studies of micromegas as a neutron detector and its track reconstruction

In this paper a two dimensional readout micromegas detector with a polyethylene foil as converter was simulated on GEANT4 toolkit and GARFIELD for fast neutron detection.A new track reconstruction method based on time coincidence technology was developed in the simulation to obtain the incident neutron position.The results showed that with this reconstruction method higher spatial resolution was achieved.     

Monte Carlo studies of micromegas as a neutron detector and its track reconstruction

In this paper a two dimensional readout micromegas detector with a polyethylene foil as converter was simulated on GEANT4 toolkit and GARFIELD for fast neutron detection. A new track reconstruction method based on time coincidence technology was developed in the simulation to obtain the incident neutron position. The results showed that with this reconstruction method higher spatial resolution was achieved.     

Discriminating cosmic muons and X-rays based on rise time using a GEM detector

Gas electron multiplier(GEM) detectors have been used in cosmic muon scattering tomography and neutron imaging over the last decade.In this work,a triple GEM device with an effective readout area of 10 cm x10 cm is developed,and a method of discriminating between cosmic muons and X-rays based on rise time is tested.The energy resolution of the GEM detector is tested by ~(55)Fe ray source to prove the GEM detector has a good performance.Analysis of the complete signal-cycles allows us to get the rise time and pulse heights.The experiment result indicates that cosmic muons and X-rays can be discriminated with an appropriate rise time threshold.     

基于读出条读出的二维位置灵敏气体电子倍增器的研制

为研发能够满足北京同步辐射(BSRF)实验要求的二维探测器,研制了基于读出条读出的二维位置灵敏X射线气体电子倍增器(GEM).实验过程中通过改进读出条的周期,并基于中科院高能所实验物理中心电子学组研制的多路电荷放大器系统与VME存储-ADC系统,对软X射线源的位置分辨率进行了精密测量且得到了优异的二维位置分辨:X方向约为84μm,Y方向约为75μm.研究了三级GEM压差之和对位置分辨的影响,并测试了探测器的位置准确度与线性.对基于阳极读出的GEM用于模拟读出测试系统得到了一定的理论认识,侧重研究了GEM探测器基于模拟读出的系统特性,给出了相关的分析与讨论.     

Two-dimensional thermal neutron detector

A two-dimensional thermal neutron detector for neutron diffraction experiments has been developed and designed at the St. Petersburg Nuclear Physics Institute, Russian Academy of Sciences. The detector is based on a multiwire proportional chamber with cathode-strip delay line readout. The detector aperture is 170 × 300 mm² and the anode wire spacing is 4 mm. The chamber is filled with a 1.5 atm ³He + 2 atm CF₄ gas mixture. To conserve high purity of the gas mixture, all electrodes are made of quartz glass. The spatial resolution of the detector is 2.5 mm and the detection efficiency is 60% for 9 Å neutrons.     

中国散裂中子源小角中子散射谱仪探测器研制

中子小角散射探测器是小角散射（SANS）谱仪的关键设备之一,探测器要求有足够大的探测面积、较高的探测效率及较好的空间分辨率,能够在真空腔中稳定地工作并可在腔体内前后移动。综合考虑,SANS探测器采用120只8 mm直径位置灵敏3He管,组成有效面积1 000 mm（X）×1 020 mm（Y）的二维探测器阵列。探测器阵列分为10个模块,每一个模块功能完全独立,包括12只3He管及其对应的读出电子学和数据获取系统。读出电子学位于探测器背面的回字形密闭腔体内,由CSNS电子学组自主研发。SANS探测器从设计、选型、样机、调试到安装历时三年,中子束流实验结果显示探测器探测效率大于50%（@2Å）,空间分辨率好于10 mm（FWHM）,完全达到设计要求,目前正在中国散裂中子源小角散射谱仪运行使用。     

Study on spatial resolution of micromegas as a neutron detector under condition of high neutron flux and γ ray background

In this paper Micromegas has been designed to detect neutrons. The simulation of the spatial reso-lution of Micromegas as neutron detector is carried out by GEANT4 toolkit. The neutron track reconstruction method based on the time coincidence technology is employed in the present work. The influence of the flux of incident 14 MeV neutron and high gamma background on the spatial resolution is carefully studied. Our results show that the spatial resolution of the detector is sensitive to the neutron flux, but insensitive to the intensity of γ background if the neutron track reconstruction method proposed by our group is used. The γ insensitivity makes it possible for us to use the Micromegas detector under condition which has high γ-rays background.     

Monte-Carlo simulation of a compact gamma-ray detector using wavelength-shifting fibers coupled to a YAP scintillation crystal

The production and transportation of fluorescent light produced in wavelength-shifting fibers (WSFs) coupled to YAP scintillation crystal is simulated using the GEANT4 codes.An advantage of the wavelength-shifting fiber readout technique over a direct readout with a position-sensitive photo-sensor is the reduced requirement for position sensitive photomultiplier tube photocathode area.With this gamma-ray detector,the gamma camera is small and flexible and has larger effective field of view and low cost.Simulation results show that a) a mean 12 of photons per 59.5 keV gamma ray interaction is produced in the WSF located nearest to the incident gamma ray,and a spatial resolution of 3.6 mm FWHM is obtained,b)a mean 27 of photons per 140 keV gamma ray interaction is produced and a spatial resolution of 3.1 mm FWHM is obtained.Results demonstrate the feasibility of this concept of a compact gamma-ray detector based on wavelength-shifting fibers readout.However,since the very low photoelectron levels,it is very important to use a photon counting device with good single photo-electron response to readout the WSFs.     

RETGEM探测器的初步测试

研制了一种新型的带有阻抗性电极的TGEM——RETGEM(Thick GEM with Resistive Electrodes)探测器, 阻抗性电极可以有效地保护探测器和前端电子学免于偶尔放电的损伤。 对RETGEM探测器进行了初步测试, 其中包括计数率、能量分辨、增益以及打火率。 结果表明, 探测器达到了设计的基本要求。 In this study we present preliminary results from a new detector: a thick gaseous electron multiplier(GEM) with resistive electrodes. The resistive electrodes protect the detector and the front end electronics from damage by occasional discharges. In different gas mixtures, we test Thick GEM with Resistive Electrodes(RETGEM) detector for the first time, including counting rate, energy resolution, effective gain, and discharge probability. The results can satisfy the basic demand of RETGEM detector design.     

三级GEM探测器的增益一致性实验研究

随着二维GEM气体探测器在X射线成像探测领域的应用, 三级GEM的探测结构和电场均匀性带来的增益一致性修正问题, 成为需要深入研究的课题内容。 介绍了有效探测面积为100 mm×100 mm的三级倍增GEM探测器, 共采用100路阵列读出, 每路读出Pad面积为9.5 mm×9.5 mm。 测量了55Fe放射源准直入射的全能峰谱。 实验表明, 随着时间的变化, 探测器的增益基本上保持稳定; 随气流的增大, 增益由变化明显到变化不大。 GEM探测器各个阵列单元的增益一致性良好（>80%）; 能量分辨率在0.18～0.22之间, 运用最小二乘法拟合给出增益一致性的修正结果, 修正后相差约0.1, 为GEM气体探测器的增益一致性修正方法提供了参考方案。 With the application of the two dimensional GEM gaseous detector in X ray imaging, the correction method of gain uniformity caused by triple GEM avalanche structures and electric field uniformity should be studied. The paper reported the study of the triple GEM detector with effective area 100 mm×100 mm used the Pad’s size of 9.5 mm×9.5 mm. In the test, 100 readout channels were designed. Results showed that gain remained stable over time; as air flow increases, gain from increases obviously to changes very little. Particularly, triple GEM’s gain uniformity was very good (more than 80%) and the range of energy resolution was from 0.18 to 0.22. To improve gain consistency of results, the difference value revised was obtained to be about 0.1 by the least square method. It provided a better method to improve gain uniformity of GEM detector.     

Study on spatial resolution of micromegas as a neutron detector under condition of high neutron flux and γ ray background

In this paper Micromegas has been designed to detect neutrons. The simulation of the spatial resolution of Micromegas as neutron detector is carried out by GEANT4 toolkit. The neutron track reconstruction method based on the time coincidence technology is employed in the present work. The influence of the flux of incident 14 MeV neutron and high gamma background on the spatial resolution is carefully studied. Our results show that the spatial resolution of the detector is sensitive to the neutron flux, but insensitive to the intensity of γ background if the neutron track reconstruction method proposed by our group is used. The γ insensitivity makes it possible for us to use the Micromegas detector under condition which has high γ-rays background.     

中国散裂中子源反角白光中子束流参数的初步测量

中国散裂中子源(CSNS)已于2018年5月建设完工,随后进行了试运行.其中的反角白光中子束线(Back-n)可用于中子核数据测量、中子物理研究和核技术应用等多方面的实验.本文报道对该中子束的品质参数测量实验过程以及最终实验结果.实验主要采用中子飞行时间法,利用~(235)U,~(238)U裂变室和~6Li-Si探测器测量了中子能谱和中子注量率,又利用闪烁体-互补金属氧化物半导体探测系统测量了中子束斑的剖面,得到了该束线的初步实验测量结果.其中白光中子的全能谱测量范围eV—100 MeV,给出了不确定度分析;给出了中子注量率两个实验厅位置的满功率值;给出了白光中子在直径60 mm情况下的全能区束斑.通过与模拟结果的比较探讨了以上结果的合理性,并提出了改进计划.这些实验结果为以后该束线的核数据测量和探测器标定实验奠定了基础.     

Simulation study on the boron-coated GEM neutron beam monitor

A Monte Carlo method of the 3D GEM simulation is introduced.The physical process of the neutron detection is described with the Geant4 code and the Garfield code.The results of the optimized electric-fields,the emitted ions spectrum,the electrons transverse diffusion and the signal width are presented.Moreover,the preliminary result with a CF-252 neutron source is reported.These are useful in designing detector structures and to provide an optimized option for the development of the boron-coated GEM neutron beam monitor.     

基于GEM探测器的时间投影室TPC的讨论

自20世纪90年代以来, GEM探测器以其高电子倍增、高空间分辨和高计数率等优势在粒子物理和辐射成像等领域得到了广泛和深入的研究, 具有广阔的应用前景. 如果将GEM作为读出探测器应用在时间投影室TPC系统上, 和传统的读出方式比较起来, 既有许多优点也有许多挑战. 目前世界上有许多机构正在研究将此方案用于将来的大型正负电子对撞机ILC. 本文论述了这些研究课题的概况, 讨论了TPC的各项关键性能指标与GEM探测器的关系及存在的问题.