用大气荧光观测超高能宇宙线的τ中微子望远镜(CRTNT)性能研究

讨论了测量超高能宇宙线的τ中微子望远镜(CRTNT)的性能. 利用Monte Carlo方法对探测器作了详细的模拟, 并研究了探测器以一个塔形主探测器和两个高视角辅探测器协同触发的布局, 以及对大气簇射作立体观测时的物理性能. 计算了当能量高于10¹⁷eV时, 探测器的有效面积. 用于第2个膝区物理研究时事例率估计可达20k个/年. 还估算了与其他探测器交叉定标的事例率. 比较和优化了探测器的不同几何布局.     

BESⅢ μ探测器阻性板模型室的性能研究

对基于酚醛树脂的阻性板室(RPC)进行研究. 通过改进的表面处理工艺, 开发了一种新的阻性板材料, 并在不同温度下对多块样板的电阻率进行了测量. 对比了基于此新型阻性板的不同电阻率RPC模型室的探测效率、计数率和暗电流. 利用¹³⁷Cs γ源和实验束流研究了流光模式RPC的抗辐照性能. 结果表明此新型阻性板RPC满足BESⅢ μ探测器的要求.     

在BEPCⅡ/BESⅢ上寻找η′c和1P1的Monte Carlo研究

使用SimBes(探测器模拟软件)和UGNT(物理事例产生器)模拟了在即将建造的BEPCⅡBESⅢ上寻找η′_c和¹P₁的过程.初步结论是如果收集到3×10⁹ψ(2S)事例,就有能力寻找这两个粒子,而且,寻找η′_c比寻找¹P₁需要更少的ψ(2S)事例.     

怀柔EAS阵列的Monte Carlo研究

用GENAS程序包为怀柔阵列产生了36万Monte Carlo模拟EAS事例,用它们研究了怀柔阵列的性能,确定了最佳的事例判造条件,对实验数据进行了正确性检验,得到了怀柔EAS Size(即簇射在观测面的总荷电粒子数)与初级宇宙线能量之间的转换关系.这项研究表明,怀柔阵列的EAS心位和方向测定精度分别好于3m和2.5°;EASSize测定误差典型值约8%;近垂直簇射的Size(N)与初能(E)的关系为E≈10^10.64N^0.84.     

80MeV/u 20Ne轰击9Be碎裂产物反应总截面的测量

介绍了用透射法测量中能区²⁰Ne打⁹Be靶碎裂产生的次级束与Si靶作用的核反应总截面的方法,以及实验的探测器布局、实验过程和实验结果.并对理论上预言有奇异结构的核¹²N,¹⁷Ne和¹⁷F的实验结果与其相邻核进行了比较.     

RPC读出条的阻抗匹配

文章对高阻板探测器读出条的阻抗匹配问题进行了研究;引入了一个用于计算带状线特性阻抗的经验公式.测量的特性阻抗与经验公式很好地符合,说明这个经验公式可以用于RPC读出条特性阻抗的计算,以改善RPC读出信号的质量,利于RPC探测器性能的测量.     

中子与9Be和6,7Li反应的次级中子发射谱实验研究

测量了8.17MeV与10.27MeV中子与⁹Be和^6,7Li作用的次级中子双微分截面. 对于10.27MeV, 为了消除从D(d,np)破裂反应来的源破裂中子对双微分截面测量结果的影响, 采用了常规多探测器快中子飞行时间谱仪和非常规多探测器快中子飞行时间谱仪相结合的办法. 用Monte-Carlo方法对实验测量得到的飞行时间谱进行了详细的模拟, 通过测量谱与模拟谱的比较, 得到了实验测量的次级中子双微分截面. 实验测量结果以n-p(常规谱仪)和n-C(非常规谱仪)弹性散射微分截面作为归一. 测量结果与评价数据以及其他测量数据进行了比较. 用一个基于Hauser-Feshbach和激子模型的轻核核反应理论模型对^6,7Li的次级中子双微分截面进行了计算, 理论计算结果与实验结果符合得较好.     

高能质子发射和冷原子核多重碎裂类型

通过高能质子发射和多重碎裂事件的关联研究了原子核多重碎裂. 在数值模拟随机Boltzmann-Langevin输运方程用于描述中能区重离子碰撞的基础上提出了冷原子核多重碎裂类型,即高能非平衡质子带走了体系很多能量,体系的碎裂是由于剧烈的、但很冷的膨胀引起的. 给出了在描述⁴⁰Ca+⁴⁰Ca反应系统中轰击能量为90MeV/u的中心碰撞时所出现的典型事例. 提出了采用4π探测器测量时可能给出的实验信号.     

BESⅢ桶部电磁量能器优化设计的Monte Carlo模拟

运用模拟软件GEANT3对铅加闪烁光纤类型的BESⅢ桶部电磁量能器(BSC)进行了模拟.研究表明,BSC中簇射的时间信息的读出有助于改善z向分辨、π⁰的质量分辨和排除假光子.模拟计算还给出了BSC能量分辨率(6%/E),方向角分辨与读出粒度的关系,π⁰质量分辨率σm/m与光输出、光纤衰减长度及读出粒度的关系,其中m为两个光子重建为π⁰的不变质量.     

三级GEM气体探测器性能的实验研究

GEM探测器是一种新型微型气体探测器(Micro-Pattern Gas Detector), 在粒子物理实验及低能X射线成像系统中有着较大的应用前景. 文章研制了一种适用于低能X射线成像和带电粒子径迹测量的三级GEM气体探测器. 使用放射源⁵⁵Fe对其气体放大特性、电荷传输效率及能量分辨本领等性能进行了实验研究, 重点研究了传输区电场对气体有效增益和能量分辨本领的影响. 实验结果表明, 三级GEM探测器的暗电流和噪声较小, 有效增益能够达到10⁵以上并稳定地工作, 对5.9keV的X射线能量分辨率可达24%, 传输区电场强度大于3000V/(cm.atm)时, 能量分辨率基本稳定在30%左右.     

近地雷暴电场与羊八井地面宇宙线关联的模拟研究

雷暴期间地面宇宙线强度变化的研究对理解大气电场加速宇宙线次级带电粒子的物理机理具有重要意义. 分析西藏羊八井ARGO实验中2012年大气电场的数据后发现, 近地雷暴电场的强度可达1000 V/cm甚至更高. 用Monte Carlo方法模拟研究了近地雷暴电场与羊八井地面宇宙线强度的关联. 当雷暴电场强度(取1500 V/cm)大于逃逸电场时, 宇宙线次级粒子中正、负电子的数目呈指数增长, 在大气深度约520 g/cm²处达到极大值, 与Gurevich等提出的相对论电子逃逸雪崩机理和Dwyer理论相符. 当雷暴电场强度小于逃逸电场时, 在所有负电场范围和大于600 V/cm的正电场范围, 总电子数目随电场强度的增大而增加; 当正电场小于400 V/cm时, 总电子数目均出现一定幅度的下降; 在电场为400–600 V/cm范围内, 总电子数目的变化与原初粒子的能量有关, 原初能量小于80 GeV时, 其次级粒子中总电子数目增加, 原初能量在80–120 GeV 范围内时, 总电子数目变化不明显, 原初能量大于120 GeV时, 总电子数目出现下降, 下降幅度约4%. 模拟结果可对羊八井ARGO实验的观测结果给予合理的解释.     

羊八井50m2RPC实验及初步测试结果

介绍了羊八井50m²电阻板室(RPC)地毯实验的结构、安装和对其性能的初步测试.测试的结果表明RPC完全能够很好地在海拔4300m,气压594mbar的羊八井宇宙线观测站正常地运行.     

ARGO-YBJ实验“Scaler模式”计数的气象效应

对中意合作西藏ARGO\|YBJ实验“Scaler模式”下次级宇宙线计数的气象效应进行了讨论, 计算了计数率与大气压强、 室外温度、 大气电场及实验大厅内温度、 湿度等5个气象参量的偏相关系数。结果表明, 大气压强与次级宇宙线计数有很强的负相关, 与室外温度也有一定的负相关, 而实验大厅顶部的大气电场与实验记录的次级宇宙线计数基本没有关联。 另外, 实验大厅内温度也是影响次级宇宙线地面测量的一个重要因素, 实验大厅内的湿度也有一定影响。 随着符合多重数的增加, 实验大厅内温度和湿度的影响变得不再重要。 另外, 对次级宇宙线计数率进行了多参量的气象效应修正。 结果表明, 这种修正是可靠的, 为进一步利用ARGO\|YBJ实验“Scaler模式”下的实验数据进行各种物理分析打下了基础。     

Study of RPC gas composition using Daya Bay RPCs

This study uses Daya Bay RPCs operating in streamer mode to investigate gas mixtures of at least 50% argon,at most 6% isobutane,and with small amounts of SF6.Isobutane is reduced to 2% without degradation of performance,and SF6 reduces the noise rate and current,as well as the signal size.This study provides quantitative relationships between basic RPC operating parameters and various gas compositions.     

针-板空气间隙流注放电起始过程的三维PIC/MCC仿真研究

流注放电作为自然界中闪电传播的预电离机制、高压输变线路间长空间间隙放电的重要初始阶段,在工业领域存在诸多潜在应用,近年来引起人们越来越多的关注.流注放电具有典型的多尺度、非线性的放电特征,实验观测中多呈现出分叉等不规则结构.为了研究其微观结构特性和行为特征,本文采用三维粒子仿真模型(PIC/MCC),着重研究了流注从针型正电极的起始和发展过程.模型采用了可变自适应网格、可变粒子权重以及并行计算等技术,有效地降低了三维粒子仿真的计算时间.通过调节针型电极上的施加电压幅值、改变气体组分及调整电极形状尺寸等,研究了放电参数变化对流注放电的分叉结构、半径等行为的影响.模拟结果表明:随着电压的升高,流注的半径及分叉数目增加;对比不同气体组分(纯氧以及不同比例氮氧混合气体),发现其对流注的分叉数目影响较为显著;针型电极结构直接影响了流注的起始时间和形貌.     

Identification of Primary Y-Rays by the Characteristics of Time-Space Structure of the Cosmic-Ray Air Showers

The time-space structure of particles for individual air showers induced by primary γ-rays and protons at the observation level is analysed by Monte Carlo simulation. It is shown that air showers induced by the primary γ-rays can be effectively separated from the air showers induced by protons (background) using the combination cuts on the arrival time fluctuation and the lateral distribution width of secondary particles in air showers. This method can be used for reducing the background of hadrons in searching for γ-ray point sources for ARGO experiment coorperated by China and Italy at Yangbajing. The effect of this method on the significance of γ-ray signals is also estimated.     

Test of BESⅢ RPC in the avalanche mode

The installation of the BESⅢ RPC system has been completed.Cosmic ray test results show that they perform very well in streamer mode and meet the BESⅢ requirements.We have tested several RPCs in the avalanche mode with the addition of extra SF6 in the gas mixture.We find an efficiency plateau that reaches～95%.and a time resolution of 1.8 ns.This demonstrates that the BESⅢ-type RPC can work in the avalanche mode as well.     

Numerical modeling of the streamer-cathode interaction in a short positive point-plane corona gap

The development of the streamer-cathode interface has been studied by computer simulation of the discharge in a short positive point-plane gap in N₂ at 26.7 kPa. Special emphasis was given to the transition from a streamer head structure to an abnormal glow discharge fall and to the identification of the cathode current signal corresponding to the streamer arrival at the cathode. The signal, taking the form of a sharp spike due to the displacement current, was found to be relatively insensitive to changes in the cathode secondary photoemission. The conduction current due to the collection of positive ions by the cathode begins to become significant in a time of some 20 ns after the streamer arrival, resulting in subsequent gradual rise in the cathode current.The authors thank the Slovak Ministry of Education, Youth and Sport for their support of this work and Dr. I. Koinár for his interest and critical revision of the text.     

脉冲电晕放电流光发展和OH自由基二维分布的发射光谱研究

流光在OH自由基的生成过程中起到重要作用。为了研究流光与OH自由基之间的关系,利用ICCD拍摄了线板式脉冲电晕放电反应器内流光的形成和发展过程,着重研究了在反应器几何结构固定的情况下,输入峰值电压对流光发展速度和流光在阴极板覆盖范围的影响。实验表明在反应器不击穿的情况下,输入峰值电压越大,越有利于流光的发展,因此生成的高能电子数量越多。此外我们还利用发射光谱法测量了脉冲电晕放电反应器内OH自由基的二维分布特性,并且与流光发展轨迹图对比。OH自由基在放电电场中的分布特性是以电极线为中心向四周扩散,浓度逐渐降低。这个结论和流光在脉冲电晕放电反应器内的发展轨迹图相吻合。     

Characterization of Nano‐Particles Using Laser‐Induced Incandescence

Laser‐induced incandescence (LII) is introduced as a valuable tool for the characterization of nanoparticles. This optical measurement technique is based on the heating of the particles by a short laser pulse and the subsequent detection of the thermal radiation. It has been applied successfully for the investigation of soot in different fields of application, which is described here in the form of an overview with a focus on work done at the LTT‐Erlangen during the last 10 years. In laboratory flames the soot primary particle size, volume concentration, and relative aggregate size have been determined in combination with the number density of primary particles. Furthermore, the primary particle sizes of carbon blacks have been measured in situ and online under laboratory conditions and also in production reactors. Measurements with different types of commercially available carbon black powders, which were dispersed in a measurement chamber yielded a good correlation between LII results and the specified product properties. Particle diameters determined by LII in a furnace black reactor correlate very well with the CTAB‐absorption number, which is a measure for the specific surface area. It turned out that the LII method is not affected by variations of the aggregate structure of the investigated carbon blacks. The LII signal also contains information on the primary particle size distribution, which can be reconstructed by the evaluation of the signal decay time at, at least, two different time intervals. Additionally, soot mass concentrations have been determined inside diesel engines and online measurements were performed in the exhaust gas of such engines for various engine conditions simultaneously providing information about primary particle size, soot volume, and number concentration. The LII results exhibit good correlation with traditional measurement techniques, e.g., filter smoke number measurements. In addition to the soot measurements, primarily tests with other nanoparticles like TiO₂ or metal particles are encouraging regarding the applicability of the technique for the characterization of such different types of nanoparticles.