Average energy loss measured in single and double electron capture collisions of He2 on Ar at low velocities

Employing the recoil ion momentum spectroscopy we investigate the collision between He2+ and argon atoms. By measuring the recoil longitudinal momentum the energy losses of projectile are deduced for capture reaction channels. It is found that in most cases for single- and double-electron capture, the inner electron in the target atom is removed, the recoil ion is in singly or multiply excited states (hollow ion is formed), which indicates that electron correlation plays an important role in the process. The captured electrons prefer the ground states of the projectile. It is experimentally demonstrated that the average energy losses are directly related to charge transfer and electronic configuration.

X-ray spectra induced in highly charged Ar-40(q+) interacting with Au surface

By use of optical spectrum technology, the spectra of X-ray induced by highly charged Ar-40(q+) ions interacting with Au surface have been studied. The results show that the argon K alpha X-ray were emitted from the hollow atoms formed below the surface. There is a process of multi-electron exciting in neutralization of the Ar16+ ion, with electronic configuration 1s(2) in its ground state below the solid surface. The yield of the projectile K alpha X-ray is related to its initial electronic configuration, and the yield of the target X-ray is related to the projectile kinetic energy.

ATOMIC PHYSICS RESEARCHES AT COOLER STORAGE RING IN LANZHOU

The commissioning of the cooler storage rings (CSR) was successful, and the facility provides new possibilities for atomic physics with highly charged ions. Bare carbon, argon ions, were successfully stored in the main ring CSRm, cooled by cold electron beam, and accelerated up to 1 GeV/u. Heavier ions as Xe44+ and Kr28+ were also successfully stored in the CSRs. Both of the rings are equipped with new generation of electron coolers which can provide different electron beam density distributions. Electron-ion interactions, high precision X-ray spectroscopy, complete kinematical measurements for relativistic ion-atom collisions will be performed at CSRs. Laser cooling of heavy ions are planned as well. The physics programs and the present status will be summarized.

The study of helicon plasma source

Helicon plasma source is known as efficient generator of uniform and high density plasma. A helicon plasma source was developed for investigation of plasma neutralization and plasma lens in the Institute of Modern Physics in China. In this paper, the characteristics of helicon plasma have been studied by using Langmuir four-probe and a high argon plasma density up to 3.9x10(13) cm(-3) have been achieved with the Nagoya type III antenna at the conditions of the magnetic intensity of 200 G, working gas pressure of 2.8x10(-3) Pa, and rf power of 1200 W with a frequency of 27.12 MHz. In the experiment, the important phenomena have been found: for a given magnetic induction intensity, the plasma density became greater with the increase in rf power and tended to saturation, and the helicon mode appeared at the rf power between 200 and 400 W.

基于ECRIS的等电荷态序列离子与氦、氖、氩碰撞反应中的多电子过程研究

本工作设计并建立了一个离子-原子碰撞实验终端。该终端具有一定的通用性，可用于我所EcRIS、ECRIS一300kV高压平台和兰州大学Zxl．7MV串列加速器。终端的设计特别考虑了气体靶实验中系统的动态真空和对高品质弱束流流强的控制。2004年7月-10月，利用我所ECRIS提供的束流，在该终端上进行了首轮实验。本工作指出，除了入射离子的电荷态和速度外，其空能级结构是碰撞反应的另一个主导因素，并在此基础上提出了等电荷态序列离子的概念。为了确定离子空能级结构对碰撞反应的影响，本工作系统研究了等速度的q＝6序列离子（C6＋、N6＋、。6＋、F6＋、Ne6＋、Ar6＋、co6＋）、q＝7序列离子（07＋、F7＋、Ne7＋、57＋、Ar7＋）、q＝8序列离子（FS＋、Nes＋、Ars＋、cos＋）、q：9序列离子（Fg＋、Neg＋、519＋、59＋、Arg＋、cag＋）和叮：11序列离子（Si1、Aill＋、Call＋）与氦、氖、氢的碰撞反应。实验证实，对于等速度、等电荷态序列离子，碰撞反应与离子种类强烈相关。利用同位素纯的13coZ作为EcRIs的工作气体，获得了纯净的全裸离子13C6＋束流，研究了13C6＋离子与氦、氖、氢碰撞反应与碰撞速度的关系。实验发现，在C6十一He的碰撞反应中，纯双电子俘获（DC）与双电子转移（DE）截面比JDcDIZ随碰撞速度的增加而明显下降，这暗示准分子俄歇机制在本能区C6＋一He碰撞反应中的贡献不可忽略。用MCBM描述离子-原子相互作用阶段，用电子蒸发模型统一处理碰撞后多电了激发态散射离子和反冲离子的衰变，作者编写了计算程序COBEEM。经典过垒模型（如ECBM和MCBM）仅用电荷态q一个参数描述入射离子，本工作实验证实了这种描述是不完备的。COBEEM程序对此问题进行了初步修正。该程序还包含了ECBM和Selberg等人提出了经验公式的计算。

高能氩离子在钇铁石榴石中的电子能损效应研究

本文对国内外快重离子在固体材料中引起电子能损效应的研究工作的历史和现状作了简短回顾，重点列举了到目前为止在钇铁石榴石（YIG）电子能损效应研究中取得的主要结果以及几种主要的理论模型。详细叙述了在兰州重离子加速器上进行1GeV氢离子辐照YIG材料的实验过程。用倾斜样品X一射线衍射（STD）、穆斯堡尔谱、饱和磁化强度测量等方法研究了辐照前后YIG样品的微观结构和物理性质变化，分析结果表明晶胞常数a, 非晶相百分数Fp随电子能损Se和辐照剂量Φt的增加而变大，而饱和磁化强度4π Ms减小．验证了YIG完全非晶化的电子能损阈值为Se＝8.3 MeV/μm和临界剂量为Φt＝1x1014 ions/cm2,在总结本次实验和国内外文献结果的基础上，提出了一个关于Fp（Se, Φt）函数的经验性的数学模型，并在模型中将材料本身的性质和电子能损及辐照剂量联系起来。

高电荷态氩离子与原子碰撞中的多电子转移过程研究

本工作建立起了符合关联测量实验装置，包括反冲离子飞行时间谱仪、散射离子位置灵敏探测器、差分拉瓦型气体喷嘴、基于微机的多参数数据获取系统以及数据分析和处理程序。在入射离子能量在80KeV～240KeV范围内，利用该装置系统研究了Arq++He，Arq++Ne和Arq++Ar（q=8，9，11，12）碰撞体系中的多电子转移规律，实验鉴别了反应中发生的各种多电子转移过程，测量了反应截面，获得了一批新的实验数据。 对于Arq++He碰撞体系，本工作主要研究了He原子的转移电离相对截面与入射离子能量和电荷态的规律，发现相对截面在所研究能区基本与入射离子能量无关，并利用核间势垒和复合分子的经典图象，描述了此碰撞体系转移电离过程发生的两种可能途径，估计了相对截面的经典上限，发现在此碰撞体系中，转移电离过程中电子关联作用起着重要的作用。 本工作系统研究了Arq++He和Arq++Ar碰撞体系中多电子转移反应截面与入射离子能量、电荷态和反冲离子电荷态的变化规律，以及反冲离子电荷态分布。研究发现，在低能高电荷态离子与多电子靶原子碰撞反应中，碰撞系统的相对运动动能对碰撞体系中的电子转移过程基本没有贡献；系统所具有的势能是碰撞体系中电子转移和靶原子电离的主要因素；在相同的入射离子条件下，靶原子电离能对电子转移有重要影响；碰撞反应中单电子过程占主要地位，而在多电子转移过程中，转移电离过程发生的几率一般大于纯的多电子俘获几率；入射离子单电子俘获截面、总电荷交换截面与入射离子电荷态成正比关系；入射离子电荷交换截面随离子俘获电子数目的增加而单调减小；入射离子俘获一个电子时，转移电离截面随反冲离子电荷态的升高而单调下降，而入射离子俘获电子数多于一个时，转移电离截面存在极大值分布现象，而且分布宽度随入射离子电荷态的升高具有增加的趋势。 本工作在分析实验现象和分子经典库仑过垒模型MCBM的基础上，提出基于MCBM描述，把高电荷态离子与原子碰撞反应中的电子转移过程分为四阶段描述的新想法，即：入射过程中的分子化→复合分子形成→复合分子解离和中间态离子的形成→多电子激发态散射离子和靶离子向末态的自电离衰变。并依据能量守恒原理，规范了处理多电子激发态离子发生自电离衰变的规则。在此基础上，对Arq++He和Arq++Ar碰撞体系中的电子转移截面进行了理论计算，通过与实验结果的对比研究发现，对在中间态形成的多电子激发态散射离子，根据这些规则进行自电离衰变修正后计算得到的结果与实验符合很好，因此，对多电子激发态离子的自电离修正是合理的，而且多电子激发态离子的自电离衰变是低能高电荷态离子与原子碰撞反应中转移电离过程发生的主要因素。

Cluster assistant generation of C2+ and C3+ ions in nanosecond laser ionization of seeded benzene beam

Cluster assisted photoionization processes of benzene, which was seeded in argon, induced by an intense 25 ns Nd-YAG laser has been studied by means of time-of-flight mass spectrometry. At the laser intensity of 10(11) W/cm(2), multicharged ions Cq+ (q = 2-3) with kinetic energy up to 150 eV were observed in the mass spectra. Strong evidences Support that these ions are formed in the Coulomb explosion of multicharged benzene cluster ions. (C) 2004 Elsevier B.V. All rights reserved.

Gas permeability of a novel cellulose membrane

A novel cellulose membrane was prepared by using amine oxides as the solvent and its mechanical performance was measured. Steady-state permeation rates of carbon dioxide, hydrogen, methane, nitrogen, oxygen, argon and helium in the homogeneous dense cellulose membrane were measured in the temperature range of 298-353 K and under gas pressures up to 1 MPa. The effect of swelling on hydrophilic membrane permeability was studied in some detail on the cellulose membrane. The difference in gas permeability between the "dry" cellulose membrane and the "water-swollen" cellulose membrane was investigated, and the gas permeability between the cellulose membrane and the Cellophane was compared. In this paper, the separation performance Of CO2 over H-2 in a "water-swollen" cellulose membrane is reported for the first time and the separation factor Of CO2/H-2 can be up to 15. (C) 2002 Elsevier Science B.V. All rights reserved.

Thermal stability, crystallization, structure and morphology of syndiotactic 1,2-polybutadiene/organoclay nanocomposite

Syndiotactic 1,2-polybutadiene/organoclay nanocomposites were prepared and characterized by thermogravimetry analysis (TGA), X-ray diffraction (XRD), polarized optical microscopy (POM), and differential scanning calorimetry (DSC), respectively. The XRD shows that exfoliated nanocomposites are formed dominantly at lower clay concentrations (less than 2%), at higher clay contents intercalated nanocomposites dominate. At the same time, the XRD indicates that the crystal structures of sPB formed in the sPB/organoclay nanocomposites do not vary, only the relative intensity of the peaks corresponding to (0 1 0) and (2 0 0)/(1 1 0) crystal planes, respectively, varies. The DSC and POM indicate that organoclay layers can improve cooling crystallization temperature, crystallization rate and reducing the spherulite sizes of sPB. TGA shows that under argon flow the nanocomposites exhibit slight decrease of thermal stability, while under oxygen flow the resistance of oxidation and thermal stability of sPB/organoclay nanocomposites were significantly improved relative to pristine sPB. The primary and secondary crystallization for pristine sPB and sPB/organoclay (2%) nanocomposites were analyzed and compared based on different approaches.

Preparation, structure and oxide ion conductivity in Ce6-xYxMoO15-delta (x=0.1-1.4) solid solutions

The Ce6-xYxMoO15-delta solid solution with fluorite-related structure have been characterized by differential thermal analysis/thermogravimetry (DTA/TG), X-ray diffraction (XRD), IR, Raman, scanning electric microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. The electric conductivity of samples is investigated by Ac impedance spectroscopy. An essentially pure oxide-ion conductivity of the oxygen-deficiency was observed in pure argon, oxygen and air. The highest oxygen-ion conductivity was found in Ce5.5Y0.5MoO15-delta ranging from 5.9 X 10(-5)(S cm(-1)) at 300 degrees C to 1.3 X 10(-2)(S cm(-1)) at 650 degrees C, respectively. The oxide-ion conductivities remained stable over 80 h-long test at 800 degrees C. These properties suggested that significant oxide-ionic conductivity exists in these materials at moderately elevated temperatures.

Density-functional study of lanthanum, ytterbium, and lutetium dimers

La-2, Yb-2, and Lu-2 have been studied by use of the density-functional methods B3LYP, BLYP, B3PW91, BHLYP, BP86, B3P86, MPW1PW91, and PBE1PBE. In these density-functional methods, the exchange functional is from either Becke's three-parameter HF-DFT hybrid exchange functional (B3), pure DFT exchange functional of 1988 (B), a modification of the half-and-half HF/DFT hybrid method (BH), Perdew-Wang 1991 (PW91), or Barone's modified PW91 (MPW1), while the correlation functional is from either Lee, Yang, and Parr (LYP), Perdew-Wang 1991 (PW91), or Perdew 86 (P86). PBE1PBE is the generalized-gradient-approximation exchange-correlation functional of Perdew, Burke, and Ernzerhof. For La-2, the calculated bond distance is in reasonable agreement with the experiment, but the calculated vibrational frequency is underestimated significantly compared with the experiment. Only BP86 and B3P86 have the best performance in reproducing the experimental dissociation energy for La-2. For the van der Waals dimer Yb-2, three functionals, B3LYP, BLYP, and BHLYP have excellent performance in reproducing the spectroscopic constants compared with both the experiment and previous theoretical studies.

Ground state of lutetium dimer by density functional methods

Bond distances, vibrational frequencies and dissociation energies for the ground state of Lu-2 were studied by density functional methods B3LYP, B3PW91, BLYP, BHLYP, BP86, B3P86, MPW1PW91, PBE1PBE and SVWN with CEP-121G and SDD basis sets. Singlet state is predicted to be the most stable. CEP-121G has a better overall performance than SDD. At CEP-121G basis set, all density functional methods used in this study perform well in reproducing the spectroscopic constants.

Geometries and electronic properties of Ta-n, TanO and TaOn (n=1-3) clusters

Geometries, vibrational frequencies, electron affinities, ionization potentials and dissociation energies of the title clusters in both neutral and positively and negatively charged states were studied by use of density functional theory. For both neutral and charged species, different initial isomers were studied in order to determine the structure with the lowest energy. Vibrational analysis was also performed in order to characterize these isomers. For Ta-2, Ta-Ta metallic bond is strengthened by adding or removing an electron, i.e. the charged species are much more stable than the neutral counterpart. For Ta-3, equilateral triangle with D-3h symmetry has the lowest energy for both neutral and charged species (near equilateral triangle for cation). TaO and its charged species have much larger dissociation energy compared with other tantalum oxides. For Ta2O and TaO2. structure with C-2v symmetry is much more stable than linear chains. For Ta3O, planar structure with doubly bridging oxygen atoms of C-2v, symmetry is the global minimum for both neutral and charged species. While for TaO3, three-dimensional structures are favored for both neutral (C-1 symmetry) and charged species (C-3v symmetry).

Determination of mercury with a flow injection quartz tube atomic absorption spectrometry

A method was developed for the determination of micro mercury in the soil, plants and the traditional Chinese medicine using flow injection quartz tube-atomic absorption spectrometry. The effect of the factors such as acidity,. the carrier solution, the flow rate of reductive solution and argon gas, etc. on the determination was studied. When vanadic oxide, nitric acid and sulfuric acid were used to decompose the sample reliable result could be obtained. The characteristic mass of the method is 59 pg, the detection limit is 0.028 mug/L, RSD is < 3.9% and the recovery is in the range of 94% &SIM; 102%.