ARGO实验探测γ暴的灵敏度研究

西藏羊八井ARGO实验是对广延大气簇射事例进行观测研究的"全覆盖式"地面宇宙线观测实验, 其主要目的之一就是探测E>10GeV的γ暴. 通过Monte Carlo模拟, 估算了ARGO实验探测10GeV γ暴所具有的灵敏度.     

羊八井ARGO实验触发效率的地磁场效应

广延大气簇射(EAS)中次级带电粒子在地磁场中偏转,影响次级粒子的横向分布.本文简要分析了羊八井宇宙线观测站不同天顶角的地磁场因子随方位角的变化,表明地磁场对从北方来的宇宙线次级粒子横向分布的影响比对南方来的大.利用蒙特卡罗方法模拟了有无地磁场情况下两个大容量的EAS样本,采用ARGOG探测器模拟程序模拟羊八井ARGO阵列的触发效率.模拟结果表明在忽略地磁场影响时阵列的触发效率确是各向同性的,有地磁场时触发效率南高于北,且原初粒子的天顶角越大,这种南北不对称性越明显.     

6H-SiC高场输运特性的多粒子蒙特卡罗研究

采用非抛物性能带模型,对6H-SiC高场电子输运特性进行了多粒子蒙特卡罗(Ensemble Monte Carlo)研究.研究表明：温度为296 K时,电子横向漂移速度在电场为2.0×104 V/cm处偏离线性区,5.0×105 V/cm处达到饱和.由EMC方法得到的电子横向饱和漂移速度为1.95×107 cm/s,纵向为6.0×106 cm/s,各向异性较为显著.当电场小于1.0×106 V/cm时,碰撞电离效应对高场电子漂移速度影响较小.另一方面,高场下电子平均能量的各向异性非常明显.电场大于2.0×105 V/cm时,极化光学声子散射对电子横向能量驰豫时间影响较大.当电场一定时,c轴方向的电子碰撞电离率随着温度的上升而增大.对非稳态高场输运特性的分析表明：阶跃电场强度为1.0×106 V/cm时,电子横向瞬态速度峰值接近3.0×107 cm/s,反应时间仅为百分之几皮秒量级.     

西藏地区近地晴天大气电场气象效应和时间变化研究

基于西藏羊八井宇宙线观测站在2006年3月至2011年6月期间记录的近地大气电场数据, 分析研究了该地区近地晴天大气电场气象效应和时间变化特征. 气象效应分析结果显示, 该地区近地晴天大气电场与三个气象参量(大气压强、温度和相对湿度)的长时间变化趋势基本一致, 并有明显的季节效应. 冬春季, 大气电场强度整体水平相对较低, 约为0.14 kV/m; 夏秋季, 电场强度水平相对较高, 为0.18 kV/m左右. 近地晴天大气电场强度与大气温度间的线性相关性最强, 拟合相关系数达到0.89; 与大气压强和相对湿度间的线性相关性相对较弱, 拟合相关系数依次为0.43和0.53. 傅里叶分析结果表明: 晴天大气电场时间变化受太阳日周期、半太阳日周期及其三、四次谐波分量调制作用, 调制强度依次减弱. 西藏地区近地晴天大气电场日变化特征呈大陆简单型, 即双峰双谷. 主、次峰谷分别出现在白天和夜间, 主峰谷出现的早晚因季节不同略有差异, 次峰谷出现的早晚因季节不同差异相对较大.     

水桶中的宇宙线

<正>在我们“真空”的宇宙中,时刻在飞行着各种高能粒子(各种原子核、电子、伽马光子等),我们称之为原初宇宙线。通过“重走宇宙线发现之旅”系列课程《宇宙线发现之旅”》^[1]《有多少宇宙线穿过我们的身体》^[2]《电离之谜》^[3],我们已经知道,当它们飞向我们的地球时,在高空会与地球大气的氮、氧等原子核碰撞,产生很多次级粒子,次级粒子再碰撞产生更多的次级粒子,这一过程叫广延大气簇射。     

雷暴电场对宇宙射线次级粒子μ 子的影响研究

西藏羊八井宇宙射线观测站的中子监测器主要探测宇宙射线次级粒子中能量在500 MeV—20 GeV的核子成分和少量的负μ子成分. 本文分析了2008—2010年观测站附近发生的62次雷暴期间中子监测器和大气平均电场仪的同步观测资料, 发现27次雷暴期间中子监测器计数率发生明显变化, 显著性S>5σ, 其中13次变化显著, 显著性S>10σ . 显著性S>10σ的13次个例信号变化百分比与地面电场场强幅值之间存在大体一致的变化趋势, 而显著性在5σ <S<10σ之间的14次个例信号变化百分比与地面电场场强幅值之间不存在相似的变化趋势. 较强雷暴当顶时中子监测器计数率变化一般不明显, 而中子监测器计数率变化明显的个例则多发生于雷暴云不当顶, 但探测器仍处于雷暴云下部正电荷层的控制范围之内时, 或者当顶雷暴处于形成或消散阶段. Dorman等把雷暴期间中子监测器计数率的变化归因于雷暴云内电场对宇宙射线次级粒子μ子的作用, 并建立了雷暴期间中子监测器计数率变化与雷暴地面电场相关联的理论. 本文分析发现雷暴期间羊八井中子监测器计数率变化与地面电场场强之间相关性较小或者没有相关性, 不支持Dorman的理论.     

钎锌矿相GaN电子高场输运特性的Monte Carlo 模拟研究

应用全带多粒子Monte Carlo模拟方法,研究了钎锌矿相GaN 材料电子的高场输运特性. 模拟中利用了基于第一性原理总能量赝势方法计算得到的纤锌矿GaN的能带结构数据. 用Cartier的方法,计算碰撞电离散射率. 计算得到了电子平均漂移速度和电子平均能量与电场的关系曲线. 电离系数的分析表明当电场强度大于1 MV/cm时,才会有明显的碰撞电离发生,量子产额的分析表明当电子的能量大于7 eV时,量子产额随能量增加迅速增大. 研究了在0—4 MV/cm电场强度范围内电子在各导带的分布,低场下电子全部位于 关键词： 碰撞电离 高场输运 能带结构 Monte Carlo模拟     

利用宇宙线大气簇射的时空特征分辨原初γ射线

利用Monte Carlo模拟程序模拟甚高能区原初γ射线和质子大气簇射过程,分析γ射线和质子簇射在观测平面上的时空结构,利用大气簇射次级粒子到达时间涨落和空间横向分布特征,进行原初γ射线成分和质子成分的有效分辨,为中意合作羊八井ARGO实验进行γ点源的寻找提供了降低强子本底的方法,该工作还估计了该分辨方法对γ信号显著性的影响.     

羊八井ARGO实验RPC模拟读出

羊八井ARGO实验正处于探测器安装及试运行阶段,整个阵列由1848个工作于流光模式的单层RPC探测器构成.依靠RPC读出条的数字读出只能测量小簇射事例的次级粒子数目,为了实现逐事例区分“膝区”原初宇宙线的成分及其能谱研究,对探测器增加了模拟读出,以实现对EAS芯区高达10⁴/m2的次级粒子数密度的精确测量.本文对RPC探测器性能及大动态范围模拟读出板的信号和性能做了初步的分析和研究     

脉冲电场防治水生生物附着

为探究脉冲电场对防治水生生物附着效果的影响因素,确定有效防治附着生物所需的最低电场条件,搭建了脉冲电场试验平台,通过人工脉冲形成线产生近似方波的脉冲,统计不同条件下大型溞死亡率和形态结构发生的变化,通过函数拟合得到了脉冲电场诱导死亡率与电场强度、总等效处理时间、脉冲注入能量密度之间的函数关系,并以某干渠工程为例介绍了脉冲电场防治大型溞的参数选取原则和平台搭建方法。结果表明,脉冲电场对大型溞的处理效果与电场强度、总等效处理时间和脉冲注入能量密度都呈正相关关系。电场强度介于0.5～1.5 kV/cm之间时,电场强度每增加0.5 kV/cm,诱导死亡率增加35%左右。电场强度高于2.0 kV/cm、总等效处理时间大于900μs或脉冲注入能量密度高于80 J/L时,脉冲电场都可以产生80%以上的诱导死亡率。     

Investigating the separatrices for the runaway threshold of cosmic ray electrons in a thunderstorm atmosphere

Using a modified GEANT4 code, we calculated the probabilities for cosmic ray electrons to become runaway particles in an electric field with a strength ranging from 0 to 5 kV/cm. About 10 million trajectories were calculated for particles with initial energies of 0.1 to 100 MeV. Instead of a single separatrix determining the region of runaway electrons, a set of curves connecting points with equal probabilities of a runaway regime (from 0 to 100%) was obtained. It was shown that not only is the threshold for a runaway regime probabilistic in character, but the critical field as well. This must be considered when calculating variations in the intensity of cosmic rays during thunderstorms.     

Dynamics of cosmic rays in the atmospheric electrostatic field and production of particles by thunderclouds

Acceleration of particles in the atmospheric electrostatic field is considered taking into account multiple elastic scattering. The critical field strength necessary for implementing runaway effect of charged particles under different initial conditions is analytically obtained. The process of cyclic particle production in strong thunderstorm fields is considered. It is shown that this mechanism can be used to describe the strong increases (sometimes with exponential segments) observed during thunderstorms in the intensity of the soft component.     

Radon contribution to single particle counts of the ARGO-YBJ detector

The ARGO-YBJ experiment is an air shower detector for gamma ray astronomy and cosmic ray studies with an energy threshold of ∼500 GeV. Working in “single particle mode”, i.e. counting the single particles hitting the detector at fixed time intervals, ARGO-YBJ can monitor cosmic ray and gamma ray transients at energies of a few GeV.The single particle counting rate is modulated by the atmospheric pressure and temperature, and is affected by the local radioactivity from soil and air. Among the radioactive elements, radon gas is of particular importance since its concentration in air can vary significantly, according to environmental conditions. In this paper we evaluate the contribution of the radon daughter gamma ray emitters to the single particle counting rate measured by ARGO-YBJ. According to our analysis, the radon gas contribution is roughly 1–2%, producing a counting rate modulation of the same order of magnitude of the atmospheric effects.     

The townsend coefficient and runaway of electrons in electronegative gas

We have studied the character of variation of the number of electrons formed in an electronegative gas (SF₆) under the action of an external electric field. At any value of the electric field strength E, the number of generated electrons exponentially increases with the distance from the cathode, while the average velocity and energy of electrons attain constant values. At small values of the reduced field strength, E/p<94 V/(cm Torr) (p is the gas pressure), the regime of electron attachment prevails that is characterized by negative values of the exponent (negative Townsend coefficients). For E/p>94 V/(cm Torr), the electron multiplication proceeds in the usual Townsend regime with positive exponents. In the intermediate region of E/p=40–160 V/(cm Torr), the electron multiplication coefficient exhibits a linear dependence on E/p. Numerical calculations based on a simple model show that the Townsend multiplication regime takes place even in very strong fields where the drag caused by ionization can be ignored. A universal function describing the electron runaway in SF₆ is obtained.     

Improving Plasma Confinement by Controlling Hard X-Ray

Since runaway electrons and magnetohydrodynamics activity can contribute to serious damage and energy losses in tokamaks,the effect of an external electric field on runaway electrons and hard x-ray spectra is investigated.Parameters such as the plasma current,the hard x-ray photons count and the mean energy of runaway electrons are measured.Positive and negative voltages of 300 V are applied at 10 ms after the plasma initiation(while the plasma is forming),at 15ms(while the plasma is stable) and at 20ms(while the plasma is fading away) to attain the most effective time of applying the external electric held.The number of hard x-ray photons has the most changes in the range of 0-200 keV when the external electric fields are applied.Also in the duration of 20-30 ms of plasma the greatest number of hard x-ray spectra is detected.When the external electric fields are applied,the mean energy of runaway electrons reduces significantly,especially at 15ms(while the plasma is stable).     

Flux variations of cosmic ray air showers detected by LHAASO-KM2A during a thunderstorm on June 10, 2021

The Large High Altitude Air Shower Observatory (LHAASO) has three sub-arrays, KM2A, WCDA, and WFCTA. The flux variations of cosmic ray air showers were studied by analyzing the KM2A data during a thunderstorm on June 10, 2021. The number of shower events that meet the trigger conditions increases significantly in atmospheric electric fields, with a maximum fractional increase of 20%. The variations in trigger rates (increases or decreases) were found to be strongly dependent on the primary zenith angle. The flux of secondary particles increased significantly, following a trend similar to that of shower events. To better understand the observed behavior, Monte Carlo simulations were performed with CORSIKA and G4KM2A (a code based on GEANT4). We found that the experimental data (in saturated negative fields) were in good agreement with the simulations, assuming the presence of a uniform electric field of -700 V/cm with a thickness of 1500 m in the atmosphere above the observation level. Due to the acceleration/deceleration by the atmospheric electric field, the number of secondary particles with energy above the detector threshold was modified, resulting in the changes in shower detection rate.     

Monte Carlo calculation of electron spectra produced in water phantoms by 20 keV-1 GeV photons

Abstract

A Monte Carlo calculation for the energy spectra of electrons and positrons produced in infinite and semiinfinite water phantoms by photons ranging in energies from 20 keV to 1 GeV are presented. The dominant processes considered are the photoelectric effect, Auger effect, Compton effect, pair, and triplet production. Bremsstrahlung produced by electrons and positrons with energies greater than 1 MeV is also included. The effect of multiple Compton scattering, not considered in the earlier calculation, for the infinite phantom for photon energies higher than 2 MeV has been incorporated. For a semi-infinite phantom, multiple Compton scattering and backscattering through the top are considered. The results are compared with the earlier calculations for the first-collision spectrum. It is found that the inclusion of multiple Compton scattering significantly increases the average number of electrons/cm³ per photon/cm² at all energies considered whereas bremsstrahlung reduces the number of high energy electrons and produces more low energy electrons in the spectrum.     

PAMELA spectrometer data processing

The international space experiment PAMELA was started in the mid-2006 and was finished in the beginning of 2016. The main objective of the experiment was the study of the cosmic ray spectra and elemental composition (including antiproton and positron spectra) in a wide energy range. The main instrument of the PAMELA device is a spectrometer including several detectors. Since the case in point here is the technique of processing the results for high-energy particles (protons, α-particles with energies E ≥ 50 GeV/nucleon, electrons and positrons with E ≥ 50 GeV), the three detectors were mostly used in data processing: a tracker placed into a dc magnetic field, a calorimeter, and a neutron detector. A relatively simple technique for separating electrons and positrons from the total flux of charged particles arriving at the spectrometer and a technique for determining the energy of these particles and constructing their energy spectra are described. This paper is based on the results presented in [1].     

On the influence of the voltage pulse rise time and cathode geometry on the generation of a supershort avalanche electron beam

The influence of the voltage pulse rise time on the amplitude of a runaway electron beam and X-ray generation in air and nitrogen under atmospheric pressure is studied experimentally and theoretically. Generalization of the whistle criterion for the case of a nonuniform field is suggested. It is shown that the maximal energy of beam electrons and the beam current amplitude grow when the voltage pulse rise time decreases. It is found that the amplitude of the runaway electron current reaches a maximum at a certain curvature of the cathode. The maximal energy of electrons increases when the radius of curvature of the cathode exceeds the value at which the beam current amplitude is the highest. If the field is nonuniform, its critical value at which many electrons run away is more than an order of magnitude lower than in the uniform field.