One and two electron transitions in multiply charged ions and helium collisions

In this paper, an extension of the already-developed and modified over-barrier model is presented to study theoretically one and two electron transitions between helium atoms and multiply charged ion collisions at a low-to-intermediate velocity (ν_Bohr ∼ 5ν_Bohr). It is found that the present model can partially reproduce the experimentally obtained velocity dependence of the absolute cross-sections which is also supported by the results of the classical trajectory Monte Carlo (CTMC) method.     

Surface physics with multiply charged ions

A program on surface physics with the ECR ion source is discussed. A first measurement, performed with a provisional set-up, will be shown.     

Electron capture into Rydberg states in collisions between multiply charged ions and hydrogen

We investigate the substate distribution σ _nlm in Rydberg manifolds (n ～ 10) following an asymmetric charge transfer reaction, C⁶⁺ + H(1s) → C⁵⁺(nlm) + H⁺, at velocities v ? 1 a.u. These calculations serve as testing ground for two novel features included in our theoretical treatment, namely, (1) the use of a multiple scattering approach, the continuum distorted wave (CDW) approximation, to describe the capture process, and (2) the explicit inclusion of the post-collision interaction (PCI) with the residual target ion to supplement the primary capture amplitude. A measure of the multiple scattering contributions is obtained by comparison with the predictions of the first Born (OBK, single scattering) approximation whereas the PCI effects are gauged by inspection of the (l, m)?distributions obtained from the resulting CDW(OBK)-PCI model with those calculated with the standard CDW (OBK) approximation.     

The decay of autoionizing states in electric field formed during collisions of multiply charged ions with metal surface

When a multicharged ion approaches the metal surface, a strong electric field occurs due to interaction between the ion and the charge induced in the metal. During ion-surface scattering, double excited autoionizing states can be formed, and their decay occurs in the presence of strong electric field. The Auger transition rates for such states are higher than those in the absence of the electric field; this is connected with the increase in the wave functions overlap and also with mixing of states with different orbital momentums. This effect changes our view on the population scheme of states with the lowest principal quantum numbers for the collisions considered.     

Theory and experiment of electron capture in collisions of multiply charged projectiles with light targets

In this joint theoretical and experimental effort, we examine in detail the capture channel in collisions of multiply charged projectiles with light targets. We report new high-resolution photon-spectroscopic results of electron capture of energetic (2–5 MeV) C⁴⁺ ions with H₂ and He, from which we extract specific (n,l) capture cross sections. The present study extends our previous work and demonstrates anew the superiority of the multiple scattering theories, here that of the continuum distorted wave (CDW) calculations, to describe the capture process. The multiple scattering contributions (absent in the usual first (single scattering) and second (single and double scattering) Born approximation) are shown to be important not only for the absolute magnitudes but also for the relative populations of the final states.     

Cross section database for carbon atoms and ions: Electron-impact ionization, excitation, and charge exchange in collisions with hydrogen atoms

A database has been constructed consisting of the recommended cross sections for electron-impact excitation and ionization of carbon atoms and ions C, C⁺-C⁵⁺, as well as for charge exchange processes between carbon ions C⁺-C⁶⁺ and hydrogen atoms. We have collected a large amount of theoretical and experimental cross section data from the literature, and have critically assessed their accuracy. The recommended cross sections, the best values for use, are expressed in the form of simple analytical functions. These are also presented in graphical form.     

Charge-changing processes in collisions of heavy many-electron ions with neutral atoms

Some features of charge-changing processes, namely, electron capture (EC) and electron loss (EL), are considered for heavy many-electron ions colliding with neutral atoms in a wide range of ion energy E = 10 keV/u-100 GeV/u. The discussion is based on cross-section calculations performed by available computer codes, namely, CAPTURE, DEPOSIT and RICODE. The RICODE (Relativistic Ionization CODE), which provides calculation of single-electron loss cross sections in the relativistic energy regime, was recently created on the basis of the relativistic Born approximation and is described in the Appendix A. In addition, a semi-empirical formula for single-electron loss cross sections is suggested based on properties of the Born approximation and numerical calculations by the RICODE program. To cover also the low and intermediate collision energies, EL cross sections are obtained by the recently created DEPOSIT code which provides calculation of single- and multiple-electron as well as the total cross sections. Based on the results obtained by these codes, recommended capture and loss cross sections for heavy ions like xenon, uranium and lead ions colliding with neutral atoms are presented over a wide energy range.     

Low-energy electrons emitted in collisions of heavy ions with solid state targets

Detailed knowledge of low-energy electron emission in collisions of swift ions with solids and gases is of utmost importance for the modeling of the dose distributions and track structures at small distances (<20 nm) in mixed radiation fields, particularly for the Local Effect Model, LEM, developed and used at GSI for the prediction of ion radiation effects in ion radiotherapy and related fields. At GSI, we have launched a project aimed at systematic investigations of the energy and angular distributions of low energy (sub-keV) electrons emitted from solids. We have commissioned an electrostatic toroidal spectrometer at the UNILAC accelerator, and we have developed a method to identify, study and analyze problems caused by the condition and constitution of the target foils and their surfaces. For this, we combined measurements of electrons emitted in collisions of low-energy electron beams (500 eV, 1 keV) with results of dedicated Monte Carlo simulations. We utilized the findings of these studies for the investigation of electrons emitted from the same targets in ion-atom collisions for the data analysis, and we report on results of our first measurements with carbon projectiles.     

Sputtering of monocrystalline and polycrystalline gold by multiply charged ions (fission fragments)

Translated from Atomnaya Énergiya, Vol. 64, No. 2, pp. 131–133, February, 1988.     

Single electron loss in the collisions of lowly charged ions and atomic hydrogen

In this paper, the projectile electron loss cross sections of He⁺, Li⁺, Li²⁺ and C²⁺ colliding with atomic hydrogen are studied in the frame work of the extended over-barrier model at intermediate velocities (25–600 keV/u). The electron loss cross sections are calculated in terms of the interaction between the screened target nucleus and the active projectile electron and of the interaction between the projectile electron and the target electron. Compared with the measurements, this model satisfactorily reproduces the experimentally obtained energy dependence of the single electron loss cross sections over the energy range investigated here.     

Energy distributions of charged and neutral hydrogen atoms backscattered from metal surfaces bombarded with 5 to 18 keV protons

Polycrystalline targets of Be, V, Nb, Mo and Ta have been bombarded with protons with primary energies in the range from 5 to 18 keV. The energy distributions of the charged and the neural particles backscattered at 135° with respect to the primary beam direction have been measured between 200 eV and 18 keV. The energy distribution of the neutrals has a pronounced maximum between 0.5 and 1 keV whose position does not depend on the primary energy or the target material, or the angle of emergence of the scattered particles. The energy distribution of the charged particles shows a less pronounced maximum between 1 and 1.5 keV. Only slight differences in the shape of the energy distributions have been observed for different target materials. The fractional number of charged backscattered particles increases from $\text{≈; 3\%}$ at 300 eV to $\text{≈; 40\%}$ at 18 keV.     

Energy-gain spectroscopy studies of state-selective electron capture for multiply charged Ar recoil ions: Comparison with the extended classical barrier model

Cross sections for capture into specific states have been measured by energy-gain spectroscopy for multiply charged argon recoils colliding with neon, argon, and xenon. The energy gains are compared with theoretical estimates based on an extension of the classical barrier model. It is found that both single-electron capture and the particular type of transfer ionization dominating these reactions are reasonably well described.