HIRFL-CSRm内靶实验终端CsI(Tl)电磁量能器性能模拟

基于GEANT4模拟了HIRFL CSRm内靶实验终端的CsI(Tl)电磁量能器系统,给出了CsI电磁量能器的最佳设计参数及可能达到的性能.结果表明,设计的CsI(Tl)电磁量能器系统能够满足所研究的物理要求. Based on the GEANT4, the performance of the electromagnetic calorimeter (EMC) of the internal-target detector at HIRFL-CSRm is simulated. The simulation results show that 1.5%—3% of the energy resolution σ_E/E and 2° of the polar angular resolution σ_θ can be obtained. The invariant mass of the π~0 decay can be reconstructed well. The performance can meet the requirement of studying the proposed physics at HIRFL-CSRm.     

HIRFL-CSRm内靶实验终端CsI(Tl)电磁量能器性能模拟

基于GEANT4模拟了HIRFL-CSRm内靶实验终端的CsI(Tl)电磁量能器系统, 给出了CsI电磁量能器的最佳设计参数及可能达到的性能. 结果表明, 设计的CsI(Tl)电磁量能器系统能够满足所研究的物理要求.     

Micromegas中子探测器位置分辨特性的Monte-Carlo研究(英文)

利用GEANT4和Garfield气体探测器模拟程序模拟了Micromegas中子探测器位置特性。 在漂移极上加一层聚乙烯薄膜作为转换材料, 通过反冲质子法测量中子的位置。 提出了一套通过设定探测器上层结构的方案来得到探测器的位置分辨特性。 通过对模拟结果的分析与比较, 得到一种易于测定探测器位置分辨特性的方法。 该工作不仅可以优化气体探测器结构设计, 缩短实验周期, 而且还能极大程度地节约经费。 In the present work, the spatial resolution of Micromegas as a neutron detector was simulated with GEANT4 and Garfield program. The polyethylene foil was used as neutron converter. A new method based on structural setting on the top layer of the detector was adopted to obtain spatial resolution. According to our simulation, it turned out to be a better spatial resolution, and this method was easily realized in experiment.     

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。     

基于GEM读出的TPC工作气体的研究

针对TPC中对于电子漂移的要求, 结合Garfield软件, 研究了我们所研制的TPC原型所用的工作气体. 分析了不同气体对于电子漂移的寿命、漂移速度、横向和纵向扩散, 以及电离特性等参数的影响; 结合分析论证, 得到了以Ar, CH₄和CF₄为主要成分的气体作为工作气体时TPC的性能指标. 并且测试了该气体中的读出GEM探测器的能量分辨率、气体增益等性能参数, 获得了很好的结果.     

BESⅢ晶体量能器设计中的蒙特卡罗研究

在BESⅢ晶体量能器的设计、研制过程中,利用7×7CsI晶体探测单元的模拟程序,对其性能做了精细的蒙特卡罗研究.给出了与非相干噪声、能量线性、晶体光输出均匀性、位置依赖等相关的模拟结果.     

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.     

北京谱仪桶部簇射计数器的改进升级

描述了北京谱仪桶部簇射计数器(BanelShowerCounter)的改进升级工作,改进后的桶部簇射计数器在能量分辨和位置分辨方面有了明显的提高,经对Bhabha事例进行离线刻度后,能量分辨好于21%,E,z向位置分辨小于3cm.     

北京谱仪桶部簇射计数器的改进升级

描述了北京谱仪桶部簇射计数器（ＢａｎｅｌＳｈｏｗｅｒＣｏｕｎｔｅｒ）的改进升级工作,改进后的桶部簇射计数器在能量分辨和位置分辨方面有了明显的提高,经对Ｂｈａｂｈａ事例进行离线刻度后,能量分辨好于２１％,ｚ向位置分辨小于３ｃｍ．     

HIRFL-CSR外靶终端上硅微条探测器阵列的搭建

硅微条探测器因具有很强的位置分辨率与能量分辨率而在世界各大核物理实验室得到广泛应用。中国科学院近代物理研究所研制了性能优越、位置精度达到0.5 mm×0.5 mm的双面硅微条探测器,用于HIRFL-CSR的外靶实验终端谱仪(ETF)上,用作径迹测量以及△E-E望远镜系统△E的探测。硅微条探测器体积小、集成度高,利用柔性印刷电路板(FPCB)引出信号,配合ASIC芯片的前端电路,能够方便地给出每一条的能量信息和位置信息。在此详细阐述了在HIRFL-CSR的ETF上双面硅微条探测器阵列的搭建,并测量了放射源在真空中探测单元的能量分辨本领。结果表明,该硅条探测器的每个探测单元对5~9 MeV能量的α粒子的能量分辨率在1%左右。     

采用光纤和YAP晶体的小型γ相机的蒙特卡罗模拟

基于波长位移光纤(WSF)耦合YAP晶体中的光子传输特性,用GEANT4软件包建立了一个蒙特卡罗模拟程序.对采用波长位移光纤耦合平板式YAP晶体的小型单管γ相机的性能进行了计算机模拟.采用波长位移光纤耦合光电倍增管光阴极面的读出方式,和晶体直接耦合光电倍增管光阴极面相比,在相同的晶体面积大小条件下,PSPMT光阴极面积可大大缩小,使费用降低.模拟结果表明：γ射线与晶体发生作用的地方所对应的光纤输出的平均光子数最少为15个,位置灵敏光电倍增管完全可以探测到.说明采用闪烁晶体－WSF－位置灵敏光电倍增管的读出方式是可行的;在用硅油耦合波长位移光纤和YAP晶体的情况下,获得的空间分辨率为1.28 mm(FWHM).模拟结果也说明了增加平均光子数对提高空间分辨率的重要性.     

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.     

Fe+注入植物种子射程实验的Monte-Carlo仿真

研究表明,TRIM程序运算结果与实验测量离子注入种子的射程分布数据相差甚远.本文根据种子微结构的特点,综合考虑多种因素,设计种子微结构模型和运算程序,用Monte-Carlo仿真不同能量（110 keV,20 keV,200 keV）、不同注量（2×10¹⁶ ions·cm^-2,5×10¹⁶ ions·cm^-2,10¹⁷ ions·cm^-2,2×10¹⁷ ions·cm^-2）的Fe⁺注入花生、彩棉、小麦种子的射程分布,结果显示本设计程序仿真的结果与实验测量数据较为吻合.所获得的注入离子与种子微结构相互作用的随机抽样模拟运算方法,为离子注入与生命体相互作用的理论研究提供新的思路.     

Study on the TU gas for the GEM-TPC detector

In this paper several different working gas mixtures for GEM-TPC were evaluated based on a Garfield simulation. Among them, Ar:CH4:CF4=90:7:3 (named herein TU gas) was selected for a detailed study because of its better performance. Some performances of drift velocity, transverse diffusion, spatial resolution and the effective number of electrons in various electric fields were obtained. The performance of a GEM-TPC prototype working in the TU gas was studied and compared with that in Ar:CH4=90:10 (P10 gas).     

Study on the TU gas for the GEM-TPC detector

In this paper several different working gas mixtures for GEM-TPC were evaluated based on a Garfield simulation. Among them, Ar：CH4：CF4=90：7：3 （named herein TU gas） was selected for a detailed study because of its better performance. Some performances of drift velocity, transverse diffusion, spatial resolution and the effective number of electrons in various electric fields were obtained. The performance of a GEM-TPC prototype working in the TU gas was studied and compared with that in Ar：CH4=90：10 （P10 gas）.     

二维位置灵敏硅探测器的应用研究

对二维位置灵敏硅探测器进行了239Puα源刻度测试,并在弹性散射实验中使用了二维位置灵敏硅探测器.考察了两种定位方法在实验中与测试中的一致性.测量了二维位置灵敏硅探测器的能量分辨率、位置分辨率和位置畸变.对位置畸变进行了定性理论解释.     

Monte-Carlo Simulation of Energy Migration in Uniaxially Oriented Polymer Films

Nonradiative electronic energy migration between identical fluorophores is studied numerically in uniaxially oriented polymer films. The reorientation effect of dipole moments induced by film stretching leads to extremely different concentration- and time-courses of emission anisotropy compared to those in disordered system. In particular, the effect of a much weaker concentration depolarization of fluorescence is due to the fact that not only primarily excited molecules contribute to emission anisotropy in oriented films.     

Auxiliary field quantum Monte-Carlo simulation of interacting electrons in quantum dots

Accurate auxiliary field quantum Monte-Carlo (AFQMC) simulations of interacting electrons in quantum dots are reported. Two different formulations of this approach are presented both of which have been designed specifically for application to quantum dots. A deflation technique for calculation of anti-symmetrized traces is introduced. The auxiliary field is sampled with a hybrid algorithm and the artificial dynamics needed for use with the present formulation of AFQMC is described. The constrained path approximation is used to control the sign problem. Results for the ground state energy of two spin-polarised, interacting electrons are presented and are found to agree well with exact diagonalization results for a wide range of screening lengths. The sign problem does not appear in the regime of small screening length.     

Studies on the drift properties and spatial resolution using a microMEGAS-equipped time projection chamber

R&D studies on the performance as well as on the gas properties of the microMEGAS-based time projection chamber with standard readout were carried out in June 2005 using 4 GeV/c pion beam in a magnetic field from 0 to 1 T at the proton synchrotron beam line at KEK, Japan. Analysis of the electron drift velocity, diffusion constant and point resolution of padrow measurement for MicroMEGAS TPC filled with 95% argon and 5% isobutane gas are presented. The underlying physical mechanism which determines the optimal TPC performance are briefly discussed. Preliminary measurements of gas properties and spatial resolution in close agreement with the analytical calculation and MAGBOLTZ simulation are summarized and presented in this paper.