Spin-polarized electrons in collisions of multicharged nitrogen ions with a magnetized Fe(001) surface

We report on the first spin-resolved energy spectra for the emission of electrons during grazing scattering of 150 keV multicharged nitrogen ions from a magnetized Fe(001) surface. A substantial spin polarization for KLL Auger electrons emitted in the final stage of the neutralization sequence during the interaction of multicharged ions with a metal surface is observed. We conclude from our data that the projectile L shell is dominantly populated by electrons from the conduction band of the target. For low energy electrons we find an increase of their spin polarization with an increase of the projectile charge.     

Binary stopping theory for swift heavy ions

The Bohr theory treats charged-particle stopping as a sequence of interactions with classical target electrons bound harmonically to their equilibrium positions. We demonstrate that equivalent results can be derived on the assumption of free binary collisions governed by a suitable effective potential. This kind of mapping is rigorous in the limits of distant and close collisions and therefore provides a tool to evaluate energy losses via binary-scattering theory. This model was developed with the aim of calculating stopping forces for heavy ions at moderately high velocities, where a classical-orbital calculation is typically superior to the Born approximation. The effective potential employed holds equally well for dressed as for stripped ions. Unlike the Bohr theory, the present evaluation avoids a formal division into regimes of close and distant collisions that do not necessarily join smoothly. Moreover, no perturbation expansion is necessary. For these reasons the overall accuracy as well as the range of validity of the Bohr model are significantly enhanced. Extensive tests have been performed, including comparisons with rigorous evaluations of the Z ₁ ³ effect, with excellent agreement even where such was not necessarily expected. Moreover, credible results have been obtained under conditions where the perturbation expansion shows poor convergence. A comparison with experimental data on O–Al is encouraging, even though shell corrections and projectile excitation/ionization have not yet been incorporated and input has not yet been optimized. Received 21 April 2000 and Received in final form 16 June 2000 An erratum to this article is available at .     

Dynamics of ionization mechanisms in relativistic collisions involving heavy and highly-charged ions

The dynamics of mechanisms associated with the ionization of inner-shell electrons in relativistic collisions involving heavy and highly-charged ions is investigated within a nonperturbative approach formulated explicitly in the time domain. The theoretical treatment is based on the exact numerical solution of the time dependent Dirac equation for two Coulomb centers on a lattice in momentum space. We present results for ionization in encounters between 100 MeV/u Au⁷⁹⁺ projectile ions impinging on a hydrogen-like uranium target. By directly visualizing the collision dynamics we identify a new ionization mechanism in which electrons are emitted from the internuclear region preferentially in the transverse direction with respect to the projectile trajectory. A striking characteristic of this ionization mechanism is that the velocity of the electron is higher than the projectile velocity. Received 26 June 2001 and Received in final form 27 November 2001     

Characteristics of alpha projectile fragments emission in interaction of nuclei with emulsion

The properties of the relativistic alpha fragments produced in interactions of ⁸⁴Kr at around 1 A GeV in nuclear emulsion are investigated. The experimental results are compared with the similar results obtained from various projectiles with emulsion interactions at different energies. The total, partial nuclear cross-sections and production rates of alpha fragmentation channels in relativistic nucleus-nucleus collisions and their dependence on the mass number and initial energy of the incident projectile nucleus are investigated. The yields of multiple alpha fragments emitted from the interactions of projectile nuclei with the nuclei of light, medium and heavy target groups of emulsion-detector are discussed and they indicate that the projectile-breakup mechanism seems to be free from the target mass number. It is found that the multiplicity distributions of alpha fragments are well described by the Koba-Nielsen-Olesen (KNO) scaling presentation. The mean multiplicities of the freshly produced or newly created charged secondary particles, normally known as shower and secondary particles associated with target in the events where the emission of alpha fragments were accompanied by heavy projectile fragments having Z ≥ 3 seem to be constant as the alpha fragments multiplicity increases, and exhibit a behavior independent of the alpha fragments multiplicity.     

低能He2+-He碰撞体系转移电离机理的实验研究

利用冷靶反冲离子动量谱仪,对低能He²⁺-He碰撞反应中产生的反冲靶离子和炮弹离子进行了符合测量,根据反冲靶离子的动量,研究了转移电离过程中的电荷转移机理.实验结果表明：在20—40 keV能量范围内,靶原子上的一个电子俘获到炮弹离子的基态,另一个电子直接发射到靶的连续态的直接电离及另一个电子俘获到炮弹离子的连续态的过程(ECC)是最主要的转移电离机理,且ECC过程主要发生在大碰撞参数条件下;炮弹离子俘获两个电子处在双激发态的自电离过程的贡献很小. 关键词： 冷靶反冲离子动量谱仪 转移电离机理 离子原子碰撞     

Production of helium projectile fragments in {16O－emulsion interactions at 4.5 A GeV/c

The measurements of partial production cross sections of the multiple helium projectile fragments emitted at 4.5 A GeV/c {}^{16}O－Em interactions are reported. We have studied the production rate of helium projectile fragments due to fragmentation of {}^{16}O ions and compared it with that obtained from different projectiles at various energies. The dependence of on the mass number of the incident beams is formulated. The multiplicity distributions of the helium fragments produced in {}^{16}O－Em interactions at different energies exhibit Koba－Nielson－Olesen (KNO) scaling. The correlation of helium projectile fragments and target fragments is also investigated and it is found that the average of target fragments is increased with the decrease of the number of helium fragments in peripheral interactions.     

Radial correlation of the helium atom in the ground state

An expression for the binding energies of electrons in the ground state of an atom is derived on the basis of the Bohr–Sommerfeld quantization rule within the Thomas–Fermi model. The validity of this relation for all elements from neon to uranium is tested within a more perfect quantum-mechanical model with and without the inclusion of relativistic effects, as well as with experimental binding energies. As a result, the ordering of electronic levels in filled atomic shells is established, manifested in an approximate atomic-number similarity. It is proposed to use this scaling property to analytically estimate the binding energies of electrons in an arbitrary atom.     

The nuclear response in high-energy hadron-nucleus interactions

In an experiment at the CERN Super Proton Synchrotron (SPS) studying hadron-nucleus interactions, slow particles which are mainly knockout protons were measured with an electronic detector. Their dependence on the target mass, incoming energy, and projectile is shown. We discuss the use of the number of protons as a measure for the number of interactions of the projectile and conclude that the emitted protons measure the impact parameter of the reaction.     

低能He~(2+)与He原子碰撞转移电离出射电子能谱研究

利用反应显微成像谱仪对70和100keV He2+与He原子碰撞转移电离(TI)过程中不同出射角度的电子能谱进行了测量,观测到出射电子能谱具有如下分布特征:出射电子速度分布介于0和入射离子速度vp之间;在不同出射角度电子能谱分布均有一极大值存在,随着出射角度的增大,能谱分布极大值逐渐减小;当电子出射角度等于45°时,多数电子集中在0eV附近。上述特征可由低能离子-原子碰撞"准分子"模型进行定性解释。在100keV He2+-He转移电离出射电子能谱中有靶电子被俘获至散射离子连续态(electron capture to continuum,简称ECC)电子的贡献,这可看做是动力学两步过程的作用。     

Differential and total ionization cross sections due to impact of swift heavy ions

In the present work, the Binary stopping power theory was used to calculate total ionization cross section and differential cross section for energy transfer from a swift heavy ion to the target electrons. The dependence on the projectile charge state is studied. The calculated values are compared with the experimental values collected from the literature.     

60AGeV 16 O诱发乳胶核反应α射弹碎片发射研究

对60AGeV^16O诱发乳胶核反应射弹α碎片的发射进行了研究，得到α射弹碎片多重数分布服从KNO标度无关性。在边缘作用下，α射弹碎片的产生与靶核碎片的产生存在线性关联，靶核碎片平均多重数随α射弹碎片数的增加线性减小，它可以很好地利用核作用几何模型来解释。     

Yields of projectile fragments in sulphur-emulsion interactions at 3.7 A GeV

This work presents the basic characteristics of singly,doubly and heavily charged projectile fragments(PFs) emitted in inelastic interactions of ~(32)S ions with photo-emulsion nuclei at Dubna energy(3.7 A GeV).Our experimental data are compared with the corresponding data for other projectiles at the same incident energy.The study of mean multiplicities of different charged PFs against the projectile mass shows a power-law relationship.The multiplicity distributions of singly and doubly charged PFs have been fitted well with a Gaussian distribution function.The yields of PFs broken up from the interactions of ~(32)S projectile nuclei with different target nuclei are studied.The beam energy dependence in terms of the various order moments is studied as well.     

Differential cross section surfaces for low energy scattering of electrons and positrons from rare gas atoms

The differential cross sections for scattering of electrons and positrons from He, Ne, Ar, Kr, and Xe at projectile energies below the inelastic thresholds are calculated using a model potential approach in which the interaction between the projectile and the target atom is partitioned into static, exchange (for electrons), and correlation-polarization parts. Two different forms of the parameter-free correlation-polarization potential are suggested; in both cases the correlation-polarization potential is determined by smoothly matching the asymptotic form of the polarization potential (1/r ⁴) to the correlation potential at the outermost orbital radius of the target atom. The results of angular distributions are presented in the form of contours of constant differential cross sections as well as in the form of differential cross section surfaces in three-dimensional plots. Both of these presentations display the locations of the principal maxima and minima of the differential cross sections as well as the critical points in a very useful manner.     

15eV的质子与羟基碰撞的动力学

采用含时密度泛函理论和分子动力学非绝热自洽耦合的方法,全微观研究沿垂直羟基分子轴向入射初动能为15 eV的质子与羟基碰撞过程的电子-离子关联动力学.计算质子和羟基动能、碰撞后羟基电子和离子的运动状态及系统电子密度的实时分布.结果表明:质子与羟基碰撞后俘获羟基的一部分电子被反弹并损失26.7%的初始动能而羟基动能增加.碰撞后丢失1%电子的羟基在保持碰撞前收缩振动的同时向计算边界平动并以93%的中性和7%的+1价的几率存在.     

Auger electron emission from metals induced by low energy ion bombardment: Effect of the band structure and Fermi edge singularity

Calculations of the kinetic energy distributions of electrons ejected from plane metal surfaces by Auger neutralization of slow monoatomic ions are reported. A many body theory is used that includes both the band structure of the target material and the Fermi singular response of metal electrons (to the sudden neutralization of the projectile). Application is made to experiments of electron emission from polycrystalline Al by Ar⁺-ions, at varying incident energies and angles. Adjustment of the broadening parameters of the distribution of shake-up electrons leads to excellent agreement between the theory and the measurements.     

Ultrahigh harmonics from laser-assisted ion-atom collisions

We present a theoretical analysis of high-order harmonic generation from ion-atom collisions in the presence of linearly polarized intense laser pulses. Photons with frequencies significantly higher than in standard atomic high-harmonic generation are emitted. These harmonics are due to two different mechanisms: (i) collisional electron capture and subsequent laser-driven transfer of an electron between projectile and target atom; (ii) reflection of a laser-driven electron from the projectile leading to recombination at the parent atom.