Measurements of K-shell ionization cross-sections of S,Ca and Zn by 7–30 keV electron impact

The absolute K-shell ionization cross-sections of S, Ca and Zn by 7–30 keV electron impact have been measured. The targets were prepared by evaporating the compounds ZnS and CaF₂ to the thick pure carbon substrates. The effects of multiple scattering of electrons penetrating the target films, electrons reflected from the thick pure carbon substrates and Bremsstrahlung photons produced when incident electrons impacted on the targets are corrected by using Monte Carlo method. The uncertainties of our measured K-shell ionization cross-sections are, respectively, ～13% for S, ～15% for Ca and ～12% for Zn. The experimental results were compared with some theoretical results and available experimental data from the literature. The experimental data for S K-shell ionization cross-sections by 7–30 keV electron impact are given here for the first time.     

K-shell ionization cross sections of Cl and Lα, Lβ X-ray production cross sections of Ba by 6-30 keV electron impact

The absolute K-shell ionization cross sections of Cl and L_α, L_β X-ray production cross sections of Ba by 6-30 keV electron impact have been measured. The target was prepared by evaporating the thin film of compound BaCl₂ to the thick pure carbon substrate. The effects of multiple scattering of electrons penetrating the target films, electrons reflected from the thick pure carbon substrates and Bremsstrahlung photons produced when incident electrons impacted on the targets are corrected by using Monte Carlo method. For Ba L-shell X-ray characteristic peaks, the spectra were fitted by using spectrum-fitting program ALLFIT to extract more accurately the L_α and L_β peak counts. The experimental results, reported here for the first time in the energy region of 6-30 keV, were compared with some theoretical results developed recently.     

Post-collision interaction after electron impact measured by (e,2e) coincidence technique

Auger electron line-shapes after electron impact inner-shell ionization of Argon at 350 eV primary electron energy have been studied by coincidence spectrometry. Emitted Auger electrons are detected in coincidence with the scattered electrons and the energy of the very slow PCI inducer ejected electron was calculated from energy conservation. The background, caused by outer-shell electrons was measured and then removed from the coincident spectrum. The effect of PCI is studied on the background-free diagram Auger spectrum. A systematic deviation was found from the line-shape given by the semi-classical approach.     

硼靶制备技术的研究

介绍Ｂ靶制备技术及其质量厚度测量方法,静电振动,高压电喷和离心沉淀主极用于制备有衬Ｂ靶,而聚焦重离子束溅射和电子轰击可用来制备自支撑Ｂ靶和有衬Ｂ靶,Ｂ靶的质量厚度用分光光度法和称重法测量。     

用薄靶厚衬底方法测量电子碰撞引起的K壳层电离截面

用能谱仪测量特征X射线,从而导出元素钛和钒的K壳层电离截面。为克服制靶困难,实验中采用薄靶厚衬底方法。通过电子输运计算,由厚衬底产生的反射电子对计数的影响得以修正。将结果和Green等的半经验公式以及Jessenberger等的测量数据进行了比较。     

厚GEM探测器对γ射线探测效率的研究

作为一种新型微结构气体探测器(MPGD),厚型气体电子倍增器（THGEM）用于较高能量光子探测是新的尝试。为了解其探测机理及探测效率的主要影响因素,利用多粒子输运软件、多物理耦合仿真软件及气体电离模拟软件,分别建立了光子与探测器相互作用模型、电子漂移扩散模型和气体电离模型。通过仿真得到了漂移极内表面和膜上电极的电子出射概率,¹³⁷Cs在漂移极内表面产生激发电子的能量分布和角分布。动态模拟了电子在特定电场中的漂移和横向扩散行为,定量计算了原初电子的入孔数量和入孔效率。最后通过实验验证,证明增大漂移区距离和提高THGEM膜间电压可显著提高THGEM对γ射线的探测效率。     

Design Studies of a Multicusp Ion Source with FEMLAB Simulation

Femlab simulations have been used to arrive at the first step in the design of an ion source. The goal is to optimize Magnetic multipole plasma confinement geometries, the increased area of constant magnetic field in the central region of the plasma volume and the increase in number of electrons which have stationary orbits within this region of the field. The confinement of electrons is essential for Multicusp ion source to produce intense beams of negative hydrogen ions (H⁻). A higher electron temperature and density given by a better plasma confinement leads to the higher efficiencies of the ionization and the production of highly charged ions. We have performed Femlab simulations of the magnetic flux density from permanent magnet used for a Multicusp ion source, plasma confinement and trapping of fast electrons by the magnetic field.     

Manipulation and optimization of electron transport by nanopore array targets

The transport of sub-picosecond laser-driven fast electrons in nanopore array targets is studied.Attributed to the generation of micro-structured magnetic fields, most fast electron beams are proven to be effectively guided and restricted during the propagation. Different transport patterns of fast electrons in the targets are observed in experiments and reproduced by particle-in-cell simulations, representing two components: initially collimated low-energy electrons in the center and high-energy scattering electrons turning into surrounding annular beams. The critical energy for confined electrons is deduced theoretically. The electron guidance and confinement by the nano-structured targets offer a technological approach to manipulate and optimize the fast electron transport by properly modulating pulse parameters and target design, showing great potential in many applications including ion acceleration, microfocus x-ray sources and inertial confinement fusion.     

Ionization and excitation collision processes of electrons in liquid water

This paper reports on Monte Carlo simulations of electrons in liquid water using a set of electron collision cross-sections constructed with data published recently. The track history of electrons having initial energy ranged from 1 keV to 10 keV is investigated looking at the ionization and excitation processes. The results show that the ratio of the ionization and excitation events per track history is unique independent of the initial electron energy above a couple of 100 eV and these inelastic processes occur with low energy electrons frequently below 100 eV. In particular, the excitation processes are dominated by the electrons below 50 eV. Flight distance distributions between the inelastic collisions are also discussed.     

Dirac-fock total energies, ionization energies, and orbital energies for uranium ions U I to U XCII

Listed here are the orbital energies, total energies, and ionization energies for ground-state configurations of uranium ions U I to U XCII. These values have been computed with the relativistic Dirac-Fock code due to Desclaux. The ground-state electronic configuration for each ion is determined by comparing the total energies of neighboring configurations and selecting the one with the minimum value. The ionization energies are obtained by building differences between the total energies of the respective ions with and without the valence electron. The term values of the uranium ions have been assigned through comparison with the term values of ionized atoms with the same configuration and the same number of electrons as given in the tables of Moore. The tables presented here should find application in the calculation of opacities in uranium plasmas.     

Effect of surface roughness on the measurement of electron impact inner-shell ionization cross sections using thick-target method

The effect of surface roughness on the measurement of electron impact inner-shell ionization cross sections in the thick-target method has been studied by using Monte Carlo simulations. The surface roughness structures were described by a series of hemispheres, which were produced randomly on the smooth surface of a thick Ni target. The characteristic X-ray yields of K-shell ionization for Ni element by electron impact near threshold energy were obtained by Monte Carlo simulations for the target with smooth surface and the targets with various surface roughnesses. The Tikhonov regularization method was applied to treat the inverse problem involved and obtain the K-shell ionization cross sections for Ni element. The comparisons between K-shell ionization cross sections of Ni element obtained for the target with smooth surface and the targets with various surface roughnesses were made. The results show that the effect of surface roughness increases as the roughness increases and the surface roughness of the target should be limited to less than 100 nm if the experimental error originated from the surface roughness would be kept less than 2%.     

Information about TS-1 and TS-2 double ionization mechanisms for positron and electron impact ionization of argon

Ejected electron angular distributions are measured for single and double ionization of argon by 500 eV positron and electron impact. Double to single ionization ratios show marked differences as a function of projectile charge. Combinations of the positron and electron data and a simple double ionization model are used to obtain differential information about the TS-1 and TS-2 mechanisms. Our analysis suggests that both mechanisms contribute roughly equally to the emission of two electrons and that interference between the two mechanisms significantly alters the ejected electron spectra.     

Ranges and stopping power of KeV electrons in the solid hydrogens

1–3 keV electron ranges and stopping power in the solid hydrogens have been investigated by the Monte Carlo simulation method on the basis of experimental thin film measurements. In the simulation, elastic scattering cross sections are calculated exactly using the single-atom crystalline potentials. Inelastic processes for gold are treated by modifying Gryziński's semiempirical expression for each core and valence electron excitation. For H₂ the ionization cross section from Green and Sawada is applied together with the gas phase stopping power from Parks et al. Simulations of electron penetration in a layer of solid hydrogen on a gold substrate with normal incidence and reflection from bulk hydrogen with different angles of incidence are fitted to experimental measurements by adjusting the stopping power of electrons in solid hydrogen. It is found to be 0.75 times the stopping power for the gas phase. The mean path length and mean penetration depth of electrons in solid hydrogen are determined from the simulations with this modified stopping power. Also the full penetration depth distributions are presented as well as their Gaussian parametrizations. The previously determined measured projected range is almost equal to the calculated mean path length.     

Transfer ionization with bare 100 keV Ne10+ ions colliding with noble gas atoms

A crossed-beam coincidence time-of-flight technique has been used to measure the charge-state distribution of rare-gas recoil ions created by fully stripped Ne¹⁰⁺ projectiles which capture one electron in single collisions at 100 keV impact energy. The results of the investigation show the importance of transfer ionization as a contribution to charge-transfer processes: with increasing target atomic number the fraction of singly charged recoil ions decreases in favor of emission of additional target electrons. For xenon, recoil ion charge states up to Xe⁵⁺ have been observed.     

Two-stage γ ray emission via ultrahigh intensity laser pulse interaction with a laser wakefield accelerated electron beam

In this study, we investigate the generation of twin γ ray beams in the collision of an ultrahigh intensity laser pulse with a laser wakefield accelerated electron beam using a particle-in-cell simulation. We consider the composed target of a homogeneous underdense preplasma in front of an ultrathin solid foil. The electrons in the preplasma are trapped and accelerated by the wakefield. When the laser pulse is reflected by the thin solid foil, the wakefield accelerated electrons continue to move forward and pass through the foil almost without influence from the reflected laser pulse or foil. Consequently, two groups of γ ray flashes, with tunable time delay and energy, are generated by the wakefield accelerated electron beam interacting with the reflected laser pulse from the foil as well as another counter-propagating petawatt laser pulse behind the foil. Additionally, we study the dependence of the γ photon emission on the preplasma densities, driving laser polarization, and solid foil.     

能损法测平均电离激发能

采用电子透过金属箔后的最可几能损测量法，由兰多公式经实验反推Ａｌ，Ｔｉ，Ｆｅ，Ｃｕ及Ｔａ平均电离激发能之实验值，所得结果与已有文献值比较有很好的一致性。实验结果表明这是一种测平均电离激发能的简便、易行且具有较高准确性的方法。     

A Monte Carlo investigation of secondary electron emission from solid targets: Spherical symmetry versus momentum conservation within the classical binary collision model

A Monte Carlo scheme is described where the secondary electron generation has been incorporated. The initial position of a secondary electron due to Fermi sea excitation is assumed to be where the inelastic collision took place, while the polar and azimuth angles of secondary electrons can be calculated in two different ways. The first one assumes a random direction of the secondary electrons, corresponding to the idea that slow secondary electrons should be generated with spherical symmetry. Such an approach violates momentum conservation. The second way of calculating the polar and azimuth angles of the secondary electrons takes into account the momentum conservation rules within the classical binary collision model. The aim of this paper is to compare the results of these two different approaches for the determination of the energy distribution of the secondary electrons emitted by solid targets.     

Factors Influencing the Electron Yield of Needle-Ring Pulsed Corona Discharge Electron Source for Negative Ion Mobility Spectrometer

A simple negative ion mobility spectrometer （IMS） is designed and used to investi- gate the factors that influence the number and efficiency of electrons generated by the needle-ring pulsed corona discharge electron source. Simulation with Ansoft Maxwell 12 is carried out to analyze the electric field distribution within the IMS, and to offer the basis and foundation for analyzing the measurement results. The measurement results of the quantities of electrons show that when the drift electric field strength and the ring inner diameter rise, both the number of ef- fective electrons and the effective electron rate are increased. When the discharge voltage becomes stronger, the number of effective electrons goes up while the effective electron rate goes down. In light of the simulation results, mechanisms underlying the effects of drift electric field strength, ring inner diameter, and discharge voltage on the effective electron number and effective electron rate are discussed. These will make great sense for designing negative ion mode IMS using the needle-ring pulsed corona discharge as the electron source.     

X射线对Kovar封装材料的剂量增强效应的Monte-Carlo计算

用 Monte- Carlo光子 -电子耦合输运程序计算了真实半导体封装 Kovar结构对不同能量 X射线在硅中的剂量增强因子 ,并与内层不涂金的 Kovar结构进行比较 ,计算了界面处两种结构进入硅的净电子数 ,结果证实了界面处产生的剂量增强主要来自界面处高 Z材料二次电子的贡献 ,该计算方法和结果为研究射线剂量增强效应提供了一种可靠的理论评估手段