Geometrical model approximation for ionization cross sections of atoms and ions in ion-atom collisions

The applicability of the geometrical model (GM) proposed in [14, 15] to calculate the ionization probability and cross section of atoms and ions during collisions with ions, including structural ions, was studied at high velocities of partners. The GM represents a version of the classical impulse approximation. It was shown that the GM in all cases under consideration allows estimation of the ionization probability and total corss section of an atom or an ion during collisions with ions with deviations of no more than 50% from the results of the classical Monte Carlo method. GM calculations are rather simple in computation respect and limit the ionization probability by unity at arbitrary impact parameters.     

About the effect of a bound state on ionization cross sections in ion-atom collisions

The cross sections σ_nl for ionization of hydrogen-like ions by heavy particles from the nl = 3s, 3p, 3d, 4s and 4p states have been calculated in the Born approximation. A structure in the energy dependence of the cross sections σ_nl and the ratios of the cross sections σ_nl/σ_1s due to the radial wave function of a bound state is discussed.     

用反应窗理论研究离子与原子碰撞的态选择微分截面

基于描述低能离子与原子碰撞的分子库仑过垒模型,详细阐述了与入射离子速度相关的反应窗理论,并对影响势垒变化的平均径向速度做了修正.根据该理论,计算了C5 -He和He2 -He碰撞体系单电子俘获过程的态选择微分截面,并分别与Kamber等人和Mergel等人的实验结果进行了比较.     

Radiative ionization in slow ion-atom collisions

Bremsstrahlung from the ionization of inner shell electrons in slow ion atom collisions is considered. The yield predicted by the binary encounter approximation is small compared with experiment in 12–33 MeV O + Zr and O + Au collisions.     

Calculated ionization cross sections for proton-fullerene ion collisions

A simple jellium model is constructed in order to obtain one-electron wave functions for the valence electrons of the fullerene. With this jellium wave function we have calculated ionization cross sections for proton-C₆₀ ⁺ collisions in the semiclassical approximation. For higher projectile velocities, for which the semiclassical approximation is valid also for electron impact, theoretical cross sections fit satisfactorily the experimental data of Völpel et al. [Phys. Rev. Lett. 71 (1993) 3439].     

Calculation of cross sections for elastic electron-molecule collisions

The phase functions and the partial and total elastic scattering cross sections for electrons with energies from 0.23 to 14.46 eV are numerically calculated on a computer for nitrogen and oxygen molecules. The phase equation in spheroidal coordinates is employed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 104–107, May, 1976.     

K-shell ionization cross sections in nearly symmetric collisions by S and Cl impact

K-shell ionization cross sections in collisions of S and Cl ions with target atoms with atomic numberZ ₂=11–22 have been measured in the energy range from 3.9 to 48 MeV. The data are interpreted in terms of the statistical model of electron diffusion to the continuum. The distribution ofK-vacancies between the projectile and the target atoms are discussed in the framework of the vacancy sharing process.     

Multiple ionization in fast ion-atom collisions: simultaneous measurement of recoil momentum and projectile energy loss

The stability of nonlinear laser light filaments in a homogeneous isothermal plasma with respect to coupled electromagnetic and density perturbations is examined. In addition to the previously known modulational instability of a trapped electromagnetic mode, a new fast growing resonant instability is found. It corresponds to the growth of an excited eigenmode in the waveguide formed by the filament density depletion, the associated density response being supersonic and transversally localized. The evolution of the instability is illustrated by numerical simulations in two and three spatial dimensions.     

低电荷态离子原子碰撞过程中的转移电离机理的研究

介绍了使用位置灵敏技术和飞行时间方法研究中低能低电荷态离子-原子碰撞过程中转移电离与单电子俘获过程.对于确定的入射离子电荷态,通过理论分析及与实验数据对比给出了转移电离与单电子俘获截面比R_TS随着入射离子速度V_P的变化规律和转移电离过程中电离的电子主要来自靶原子的最外亚壳层. 关键词： 转移电离 逃离半径 电离半径 俘获半径     

Mutual projectile-target ionization via the two-center dielectronic interaction in relativistic ion-atom collisions

We study mutual ionization in relativistic collisions between hydrogenlike projectiles and helium atoms: X(Z+)(1s)+He(1s(2))-->X((Z+1)+)+ He+(1s)+2e(-). At high collision velocities and for not too heavy projectiles, 2Z/v<1 (v is the collision velocity), the mutual ionization proceeds via the direct interaction between two electrons bound (initially) to different colliding particles. Considering for the first time this fundamental process in the case of relativistic collisions, we calculate ionization cross sections and discuss manifestations of relativistic effects. In particular, we predict two novel and interesting phenomena: (i) considerable relativistic effects in collisions with low Lorentz factors gamma and (ii) the rapid saturation of these effects at higher gamma. Estimates show that the predicted effects can be experimentally tested using existing facilities and spectrometers.     

Differential cross sections of positron-hydrogen collisions

We make a detailed study on the angular differential cross sections of positron–hydrogen collisions by using the momentum-space coupled-channels optical(CCO) method for incident energies below the H ionization threshold. The target continuum and the positronium(Ps) formation channels are included in the coupled-channels calculations via a complex equivalent-local optical potential. The critical points, which show minima in the differential cross sections, as a function of the scattering angle and the incident energy are investigated. The resonances in the angular differential cross sections are reported for the first time in this energy range. The effects of the target continuum and the Ps formation channels on the different cross sections are discussed.     

电子与高电荷离子碰撞的细致能级电离截面的相对论计算

电子离子碰撞电离的细致能级截面在X射线激光等需要确定能级布居数的高技术研究中有非常重要的意义.本文给出了在全相对论框架下利用扭曲波波恩交换近似计算细致能级电离截面的方法.作为示例,计算了若干高电荷离子细致能级的电离截面,并分析了组态相互作用的影响.计算结果与其它理论值进行了比较,获得了较好的符合.     

Excitation and ionization cross sections of hydrogen-like atoms in collisions with relativistic highly charged ions

The relativistic eikonal approximation and a matching procedure are used to describe excitation and ionization of hydrogen-like atoms from an arbitrary discrete energy state by the impact of a highly charged relativistic bare ion. Bethe-type formulas are derived that are asymptotically valid in the limits of v → c and Z ? 1, where v is the relative collision velocity, c is the speed of light, and Z is the ion charge.     

Calculation of the differential cross sections of excitation and ionization of a helium atom by electrons

Equations for the amplitudes and differential cross sections of electronic excitation and ionization of a helium atom are derived in the approximation of a frozen ion core. The wave functions of the discrete states are chosen in the form of generalized hydrogenlike orbitals. The radial wave functions of the continuous spectrum are determined by solving the equation of motion numerically. The differential excitation cross sections of excitation of the 2p, 3p, and 4p levels and ionization of a helium atom by electrons are calculated in the energy range up to 50 eV. Estimates are obtained for the nonorthogonal wave functions in the amplitudes of the excitation and ionization processes. It is shown that the given method is more compatible with experiment than the Born method.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 48–57, December, 1994.     

Stripping cross sections in collisions of light nuclei

By evaluating all the contributions of the intermediate states of the multiple scattering theory diagrams, we compute the integrated stripping cross sections of collisions among light nuclei. The resulting expressions have the simple form of a combination of total inelastic cross sections of nuclear reactions with projectile nuclei differing in the atomic mass number. We also check the accuracy of some widely used relations in heavy ion collisions. Received: 18 March 1998     

Modified over-barrier model for ionization cross sections of atomic hydrogen by multiply charged ions

The impact ionization of atomic hydrogen in collisions with H⁺, He²⁺, Li2,3+, C2,3,4,5,6+, N2,3,4,5+, O2,3,4,5,6+, and Ar3,4,5,6+ ions has been studied by the modified over-barrier model at low-to-intermediate velocities. Compared with the calculated results of the classical trajectory Monte Carlo (CTMC) method and the unitarized-distorted-wave approximation (UDWA), this model satisfactorily reproduces the experimentally obtained velocity dependence of the absolute ionization cross sections at intermediate impact velocities.