Electron Loss Cross Sections Research Articles

Absolute cross sections for electron loss, electron capture, and multiple ionization in collisions ofC3+with noble gases

Absolute charge-state-correlated cross sections for projectile electron loss, electron capture, and target multiple ionization in collisions between ${\mathrm{C}}^{3+}$ ions and noble gases have been measured for energies between $1.3$ and $3.5$ MeV. The data have been compared with other similar absolute cross sections existent in the literature for several projectiles. Calculations for the single-loss$\ensuremath{-}$multiple-ionization channel have been performed for the screening mode, using both an extended version of the classical-impulse free-collision model and the plane-wave Born approximation (PWBA), and for the antiscreening mode within the PWBA. The energy dependence of the average number of target active electrons which contribute to the antiscreening has been described by means of a simple function, which is ``universal'' for noble gases but, in principle, projectile dependent. A method has been developed to obtain the number of active target electrons for each subshell in the high-velocity regime, which presented physically reasonable results. Analyses of the dependences of the single-capture and transfer-ionization (SC and TI, respectively) processes on the projectile charge states showed that, for He, equally charged bare and dressed projectiles have very similar cross sections; the latter thus acting as structureless point charges. A behavior similar to that in the SC has been observed for the pure single ionization of He by projectiles with different charge states and of the other noble gases by singly charged projectiles. It has been shown that the ${q}^{2}$ dependence of the pure-single and total-ionization cross sections, predicted by first-order models, is only valid for high-collision velocities. For slower collisions, the electron capture process becomes more relevant and competes with the ionization channel, a feature which grows in importance as the projectile charge state increases.

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 +, Li 2+ and C 2+ 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.

Experimental electron loss and capture cross sections in ion–atom collisions

This work presents a compilation of experimental data for electron capture and loss cross sections obtained at the Scobeltsyn Institute of Nuclear Physics for neutral atoms and negative and positive ions with nuclear charge Z = 2–36 in collisions with atomic and molecular gases. The charge-changing cross sections are summarized in tables with the reference list attached.

Single and multiple projectile electron-loss and capture of low charge states of oxygen beams colliding with the methane molecule

The projectile electron loss and capture are important ionization components collision channels in dressed ion-atom and ion-molecule collisions. They play important roles in several processes connected to the penetration of neutral and charged projectiles in gases, in radiation damage and upper atmospheric physics. In this work, cross sections for total single and multiple electron loss and capture of O-, Oo, O+, O2+ projectiles impinging on the methane molecule were measured in the 15 keV ≤ E ≤ 1000 keV energy range. In addition, an extended version of the free-collision model was employed for the calculation of the electron loss cross sections. Multiple electron loss was analyzed within the independent particle model.

Electron loss and multiple electron capture of Li-like ions colliding with Ne and Ar targets

Absolute cross sections for projectile single electron loss and single and double electron capture of B2+and C3+ ions colliding with Ne and Ar in the energy range from 0.1 to 4.0 MeV were measured. Calculations for the single capture channel were performed using the Bohr-Lindhard model, showing good agreement with the experiment. For the single electron loss, calculations were made using an extended version of the free-collision model for the screening mechanism, added to antiscreening cross sections calculated within the PWBA. The calculations provided very good descriptions of the measured data. Scaling laws were obtained for the single-electron loss by both targets.

Projectile electron loss in collisions of Ar6+ and Ar8+ ions with He and Ar atoms

Multiple electron loss of fast Ar6+ (10.2 MeV amu−1) and Ar8+ (19 MeV amu−1) ions in collisions with neutral helium and argon target atoms is analysed in the independent particle model. It is found that losses from inner shells are significant such that subsequent Auger electron emission processes cannot be neglected. The Auger processes are taken into account on the level of a statistical model introduced recently. Total cross sections for multiple electron loss are calculated and compared with experimental data. In particular, ratios of q-fold to single ionization are described well.

Electron loss and multiple electron capture ofB2+andC3+ions colliding with Ne and Ar targets

Absolute cross sections for the projectile single-electron loss and single- and double-electron capture of ${\text{B}}^{2+}$ ions colliding with Ne and Ar targets and ${\text{C}}^{3+}$ ions colliding with Ar targets, in the energy range from 0.1 to 4.0 MeV, have been measured. Cross sections for the single capture channel have been calculated using the classical Bohr-Lindhard model, showing good agreement with the experiment. In the single electron-loss process, calculations were performed using both an extended version of the classical-impulse free-collision model and the plane-wave Born approximation (PWBA) for the screening mechanism, added to antiscreening cross sections calculated with the PWBA, thus providing total single electron-loss cross sections. The total cross sections obtained from the former method provided very good descriptions of the single electron-loss measured data, much better than those from the PWBA. The antiscreening calculations have been compared to experimental cross sections for ionization of ${\text{B}}^{2+}$ and ${\text{C}}^{3+}$ ions by electrons, within the independent-particle model, showing a good agreement in the asymptotic high-velocity region.

Calculation of charge-state distributions of accelerated ions in gas media

Charge-state distributions of medium-mass ions passing through H2 or He gas targets were calculated by means of a Monte Carlo code that only uses semiempirical formulae for electron-capture and electron-loss cross sections as inputs. A good agreement with experimental data was achieved. In this paper, we suggest the use of these calculations to study the effect of nuclear fusion reactions on the atomic electrons of the reactants, and on the ionic charge state of the products.

Calculation of cross sections of simultaneous ionization in ion-atom collisions by the generalized geometrical model

The geometrical model (GM) of ionization in ion—atom collisions [8, 9] was generalized to describe ionization of both colliding particles (simultaneous ionization) due to electron—electron interaction. The generalized GM (GGM) allows calculation of the cross sections for electron loss by an incident particle with simultaneous target ionization at collision velocities higher than characteristic electron velocities, accurate within a factor of two with respect to the Born or impulse approximation. An advantage of the GGM, except for its simplicity, is easy calculation of p(b) (p is the ionization probability and b is the impact parameter), which makes it possible to include the contribution of simultaneous ionization into more general approximate schemes for calculating cross sections of multielectron ionization of atoms or ions.

Single- and multiple-electron loss cross-sections for fast heavy ions colliding with neutrals: Semi-classical calculations

Extensive calculations of single, multiple and total electron-loss cross-sections of fast heavy ions in collisions with neutral atoms are performed in the semi-classical approximation using the DEPOSIT code based on the energy deposition model and statistical distributions for ionization probabilities. The results are presented for Ar 1+, Ar 2+, Kr 7+, Xe 3+, Xe 18+, Pb 25+ and U q+ ( q = 10, 28, 39, 62) ions colliding with H, N, Ne, Ar, Kr, Xe and U atoms at energies E > 1 MeV/u and compared with available experimental data and the n-particle classical-trajectory Monte Carlo ( nCTMC) calculations. The results show that the present semi-classical model can be applied for estimation of multiple and total electron-loss cross-sections within accuracies of a factor of 2. From calculated data for the total electron-loss cross-sections σ tot , their dependencies on relative velocity v, the first ionization potential I 1 of the projectile and the target atomic number Z A are found and a semi-empirical formula for σ tot is suggested. The velocity range, where the semi-classical approximation can be used, is discussed.

Analysis of the relationship between the electron-capture and electron-loss cross sections for carbon ions

The electron-loss cross sections σi, i + 1 and the electron-capture cross sections σi, i − 1 for carbon ions with energies of 35–330 keV/nucleon in hydrogen and neon are determined from experimental data. It is demonstrated that, for particle energies which satisfy the condition σi, i + 1 = σi, i − 1 or σi, i − 1 = σi − 1, i, the average equilibrium ion charge can be evaluated without solving the system of differential equations for charge exchange. The dependence of the average equilibrium ion charge on the ion energy is investigated for carbon ions.

Dissociative and non-dissociative charge-changing processes in 1.0-2.0 MeV/u O5+ + O2 collisions

In the present work molecular ionization and dissociation correlated with projectile single electron capture and loss is investigated as a function of energy for O5+ + O2 collisions. Coincidence recoil-ion spectra as well as total projectile charge-changing yields were measured for projectile energies of 1.0, 1.5, and 2.0 MeV/u. Charge states for dissociative and non-dissociative recoiling products of the target molecular oxygen were identified. Ratios of charged molecular fragment yields to single non-dissociative ionization yields as a function of projectile energy were determined as well as total cross sections for projectile single electron capture and loss.

Electron loss of fast many-electron ions colliding with neutral atoms: possible scaling rules for the total cross sections

General features of the total electron-loss (projectile ionization) cross sections, σtot, for fast many-electron ions colliding with neutral atoms are investigated. Two independent scaling laws for σtot are obtained: one follows from the experimental data and another one from the classical calculations based on the n-particle classical trajectory Monte Carlo (nCTMC) and semi-classical treatments. The semi-classical method has recently been developed based upon the energy deposition model and the statistical ionization probabilities. Both scaling relations are expressed in terms of the projectile velocity v, its first ionization potential I1 and the nuclear charge ZA of the target atom. The accuracy of the scaling relations suggested is a factor of 2–3. At the high-velocity region (v2 ≫ I1), experimental data are found to decrease approximately as σtot ∼ v−2, i.e., close to the Born ionization cross section. At low energies, the σtot values are better described by the classical approximation which accounts for multi-electron-loss processes. These scaling laws obtained are compared with a known scaling law for the Ar target and are used for the prediction of the total electron-loss cross sections in a wide range of the collision parameters. The predicted cross sections σtot can be approximately evaluated as a minimum cross section obtained from two scaling formulae.

Electron-loss cross sections for heavy-ion beam probe using gold beams: experiment and theory

We present cross section experimental data required for modeling beam production, attenuation and energy loss in the heavy-ion beam probe technique, namely, electron-loss cross sections for anionic gold projectiles and Ar and N2 targets in the energy range from 30 keV to 1 MeV. The results agree well with low-energy measured values from the literature for the Ar target. The present results are also compared with literature results for the H− projectile and the Ar target, displaying similar velocity dependences. This similarity led to the use of a simple semi-classical model to calculate the projectile-electron-loss cross sections in a wide energy range. This model employs the total scattering cross sections for free electrons and the momentum distribution of the Au− electrons. The present experimental results are in good agreement with this model, allowing a reliable estimate of the cross section values up to 100 MeV. Our results indicate that previously calculated cross sections are overestimated by at least a factor of two. This previous overestimation of electron-loss cross sections leads to significant errors in the modeling of charge-state fractions of gold beams, with consequences in the optimization of beam energy resolution and intensity for HIBP with megaelectronvolts gold beams.

Asymptotics of the cross section of the electron loss by fast ions in light media

The dependence of the single electron loss cross section on the nuclear charge Z of a projectile and on the nuclear charge Z t of a target atom for fast collisions is studied theoretically using the plane-wave Born approximation and the sum rule. The results of calculations for fast singly and triply charged ions show that the single electron loss cross section increases monotonically as Z and Z t increase. This can be used to interpolate cross sections of processes if there are no experimental data. The results of calculations compare with the experimental and theoretical data of other authors.

Polarization effects on the cross-section of ion–atom collisions

Coupled-channel cross-sections for electron capture, ionization and electron loss due to polarization effects are calculated. The maximum impact parameter for electron escape is analyzed within the classical framework. The probabilities of ionization and capture are analyzed simultaneously by a semi-empirical method. Differing from the n-body classical trajectory Monte Carlo method, the condition for electron escape is determined by Coulomb forces related to the two nuclei. This method can be used to calculate coupled-channel cross-sections rather than single-channel ones in other methods. Therefore the calculated results can be compared with experimental data directly. In the low energy range, neglecting the ionization effect, the single-capture cross-sections of hydrogen atoms induced by various partially-stripped ions were calculated. In the high energy range, neglecting the capture effect on ionization, the pure-ionization cross-sections of neon atoms induced by Ne q + ( q = 4, 6, 8) and Ar q + ( q = 4, 6, 8, 10) at an incident energy E = 1.05 MeV/u were calculated. Good agreement was found between our calculation and experimental data in the literature. This method had been partially applied for intermediate energy successfully.

Charge exchange of medium energy H and He ions emerging from solid surfaces

Charge exchange of medium energy H and He ions emerging from clean solid surfaces is studied extensively using a toroidal electrostatic analyzer with an excellent energy resolution. The charge distributions of He ions scattered from sub-monolayers near a surface are non-equilibrated, resulting in a surface peak even for poly-crystal solids. By solving simultaneous rate equations numerically, we derive electron capture and loss cross sections for Ni and Au surfaces. Based on a free electron gas model, non-equilibrated He+ fractions dependent on emerging angle reveals uniform electronic surfaces for metals and corrugated surfaces for Si and graphite with covalent bonds. It is also found that equilibrium charge fractions of H+ are independent of surface materials (Z2) and in contrast equilibrium He+ fractions depend pronouncedly on Z2. The data obtained are compared with semi-empirical formulas.

Theoretical Investigation on Excitation, Ionization and Capture in H(1s, 2s) + H(1s, 2s) Collisions

Cross sections of electron-loss in H(ls)+ H(ls) collisions and total collisional destruction of H(2s) in H(ls) + H(2s) collisions are calculated by four-body classical-trajectory Monte Carlo (CTMC) method and compared with previous theoretical and experimental data over the energy range of 4–100 keV. For the former a good agreement is obtained within different four-body CTMC calculations, and for the incident energy Ep > 10keV, comparison with the experimental data shows a better agreement than the results calculated by the impact parameter approximation. For the latter, our theory predicts the correct experimental behaviour, and the discrepancies between our results and experimental ones are less than 30%. Based on the successive comparison with experiments, the cross sections for excitation to H(2p), single- and double-ionization and H- formation in H(2s)+H(2s) collisions are calculated in the energy range of 4–100keV for the first time, and compared with those in H(ls)+H(ls) and H(ls)+H(2s) collisions.

Single-and-double electron loss of O2+ in collisions with argon and helium

This paper reports that the ratios of double to single electron loss cross-section (R) of O2+ in collision with Ar and He at the velocity of 1–4ν0 (ν0 is the Bohr velocity) have been obtained by the coincidence technique. The trend of R – V in the experiment indicates that the effective charge varies with injected velocity. The effective charge can be obtained by the n-body classical trajectory Monte Carlo method, which is interpreted by the molecular Coulomb over barrier model.

Single electron loss by fast ions in helium

The single electron loss cross sections for fast B, N, and Ne ions colliding with He atoms are calculated. In the calculation of the ionization amplitude, the He nucleus screening is taken into account by both the sum rule and the summation over a finite number of excited 1snl (n < 5, l < 2) states and states of the continuous spectrum. The calculated results agree satisfactorily with experimental data.