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.     

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.     

Study of the Ignition Requirements and Burn Characteristics of Aneutronic Fusion in Degenerate Plasma

The reactions such as; D?+?³ He and p?+?¹¹B are aneutronic fusion reactions that, in characteristic conditions create degenerate plasma. The electronic stopping power of degenerate plasma is smaller than the classical plasma, because some transitions between the electron states are forbidden. The equations that predict the behavior of these plasmas are different from the classical ones, and this is the main factor in decreasing the ignition temperature of the plasma. In this research, the nuclear fusion in deuterium–helium with a small seeding born, D/³ He/¹¹B, is considered using a time dependent model based on nuclear reactions, including ion-electron collisions, Bremsstrahlung losses and mechanical expansion. The effect of the initial born concentration on ignition temperature and energy gain is analyzed with calculating the effect of radiation loss in ignition temperature.     

An Experimental Apparatus for Low Energy High Charge Heavy Ions to Study Collisions on Atomic Hydrogen

The design and performance of a recoil ion source system which includes a recoil ion source, atomic hydrogen thermal oven target and an electrostatic analysis system will be discussed. The recoil ion source produces low velocity highly charged ions via collisions between heavy fast pump beams from the EN tandem accelerator and target gases. Time-of-flight techniques provide initial recoil charge state separation. Collisions of the recoils with atomic hydrogen are being studied. The atomic hydrogen is provided by a thermal oven which features long life time operation and low input power requirements. Dissociation fractions of 80% are achieved for 300 watts of input power. A hemispherical electrostatic analyzer allows the final charge states of the recoil ions to be determined thereby allowing the measurement of charge exchange processes for an energy range of 100 eV/q to 5000 eV/q for the incident recoil ions.     

Dielectronic recombination lines of C

The present paper presents atomic data generated to investigate the recombination lines of C ii in the spectra of planetary nebulae. These data include energies of bound and autoionizing states, oscillator strengths and radiative transition probabilities, autoionization probabilities, and recombination coefficients. The R-matrix method of electron scattering theory was used to describe the C²⁺ plus electron system.     

The ORNL ECR multicharged ion source

A multicharged ion source based on electron cyclotron resonance (ECR) heating has been designed and built at ORNL. The ECR ion source, which is completely dedicated for atomic physics collisions studies, produces higher charge states and higher beam intensities than the present ORNL PIG multicharged ion source, and will thus permit study of collision processes involving ions of higher charge states in experiments requiring higher beam intensities than could be previously obtained in our laboratory. The source has already produced up to fully stripped C and O beams, as well as up to He-like Ar beams. Measurements of the energy spread of ions extracted from the ion source operating in both single-stage and two-stage mode are described. In addition, initial results of total cross section measurements for fully stripped light ions incident on atomic hydrogen in the energy range 0.2–10 keV are presented.     

Transfer ionization with bare 100 keV Ne10+ ions colliding with noble gas atoms

A crossed-beam coincidence time-of-flight technique has been used to measure the charge-state distribution of rare-gas recoil ions created by fully stripped Ne¹⁰⁺ projectiles which capture one electron in single collisions at 100 keV impact energy. The results of the investigation show the importance of transfer ionization as a contribution to charge-transfer processes: with increasing target atomic number the fraction of singly charged recoil ions decreases in favor of emission of additional target electrons. For xenon, recoil ion charge states up to Xe⁵⁺ have been observed.     

(n,l)−Subshell electron capture cross sections in collisions of C4+, N5+ and O6+ with atomic hydrogen

By means of VUV-photon spectroscopy we have determined absolute Subshell selective electron capture cross sections σ_nlfor collisions of helium-like carbon, nitrogen and oxygen ions with atomic hydrogen, in the velocity range 0.1–0.5 a.u.The atomic hydrogen beam target was produced by means of a radio-frequency discharge source, and absolutely calibrated by measuring atomic and molecular radiation in the visible region produced by electron impacts.For all systems studied we find that the total capture cross section (σ_t = Σ_nlσ_nl depends only weakly on the impact velocity, and is in good agreement with published results from other authors. In contrast to σ_t, the Subshell selective cross sections σ_nl are strongly velocity dependent.Our results are compared with recent calculations by Fritsch and Lin; the agreement is quite satisfactory.     

The lamb shift in hydrogen-like atoms, 1 ⩽ Z ⩽ 110

Theoretical energy levels and energy-level separations for n = 1 and n = 2 states of hydrogen-like atoms with nuclear charge numbers in the range 1 ? Z ? 110 are tabulated. Quantum electrodynamical corrections of first and second order in the fine-structure constant α are included, together with finite nuclear size corrections, reduced mass corrections, and recoil corrections.     

Beam-foil interaction of highly ionized chlorine ions in the high energy region

Distributions of charge states and multiple scattering widths of angular distributions have been simultaneously measured using a two dimensional-position sensitive detector for 150 MeV ³⁷Cl¹⁰⁺ ions emerging from carbon foils with thickness of 2.5–180 $\text{μg}\text{cm}{}^2$. For thinner foils, the scattering angle dependence of mean charge states verifies the evidence for the so-called single violent and/or plural collisions     

Inelastic processes in Ne collisions with a Mg surface; charge fractions and surface roughness

Results of a study of inelastic scattering in Ne⁺ collisions with a polycrystalline Mg target, performed by measurements of charge fractions, are reported. In agreement with previous studies, ion production is found to be due to binary collisions with surface atoms and the charge fractions can be well described by a simple exponential dependence on the perpendicular velocity in the outgoing trajectory. This is also shown to be the case for Ar⁺ collisions. Charge fractions and angular distributions of scattered particles are strongly affected by surface roughness effects.     

Energy-angle distribution measurements for 0.8v020Ne and 209Bi ions penetrating thin carbon foils

Energy-angle distributions have been measured for 0.8v₀, (v₀ = Bohr velocity) Ne and Bi ions penetrating through carbon foils. Comparing the results with a Monte Carlo computer simulation that included an angle dependence only for the elastic collisions, we have observed for Ne projectiles an angle-dependent inelastic loss which, for small angles, is much larger than the elastic contribution in the case of thin foils. In the case of Bi, the energy loss distribution is dominated by elastic collisions. The calculations of Meyer, Klein and Wedell, and Ellmer and Wedell cannot describe the experimental results. The multiple scattering distributions are in agreement with both analytical and Monte Carlo calculations.     

State promotion and neutralization оf ions near metal surface

When a multiply charged ion with charge Z approaches the metal surface, a dipole is formed by the multiply charged ion and the charge induced in the metal. The states for such a dipole are promoted into continuum with decreasing ion-surface distance and cross the states formed from metal atom. The model proposed explains the dominant population of deep bound states in collisions considered.     

Charge transfer in collisions of protons with water molecule at high projectile energies and small scattering angles

The electron capture process induced by fast protons impinging upon water has been theoretically studied for very small scattering angles. Singly differential and total cross sections have been calculated for scattering angles ranging from 0 to 0.5 mrad and compared to the existing experimental data. For the sake of comparison, we have also presented the theoretical charge transfer cross sections for proton-helium collisions.     

Dynamics of molecular collisions with surfaces: Excitation,dissociation and diffraction

Aspects of molecular collisions with surfaces are discussed which are important in the chemically relevant energy range of ∼ 1–10 eV. In particular, the role of charge transfer, potential energy surface topology and intramolecular ground and excited-state potential curves are investigated as they pertain to internal vibrational excitation, dissociative adsorption or scattering, and diffractive scattering. The modeling and analysis is based on classical trajectories and semiclassical wavepacket dynamics, both for intramolecular and translation     

Semiempirical thermonuclear reaction-rate data for intermediate-mass nuclei

Given here are analytic formulas and fitting parameters which adequately represent the results of statistical thermonuclear reaction-rate calculations for over 300 target nuclei having atomic numbers in the range 8 ≤ Z ≤ 36 (oxygen through krypton) for temperatures in the range 5 × 10⁷ ≤ T ≤ 10¹⁰ K. These parametrized formulas will be useful to those involved in calculations of energy generation and nucleosynthesis in thermal environments as in stars and supernovae. All exoergic binary reactions involving an intermediate-mass nucleus reacting with n, p, α, or γ in an entrance or exit channel are considered. Ratios for determining the reverse reaction rate are given. These reaction rates have been calculated using global Hauser-Feshbach theory under the assumption that the incident particles have achieved an equilibrium distribution of center-of-mass energies and that all the excited states of each target nucleus are in equilibrium with the ground states of those nuclei. Experimentally determined excited states have been employed in the calculations where available. Otherwise a theoretical nuclear level-density expression was used. Parametrized nuclear partition functions are given for 0 ≤ T ≤ 10¹⁰ K as well as nuclear level-density information.     

Influence of the projectile charge state on the ionization probability of sputtered particles

We present a computational study of the effect of the projectile charge state on secondary ion formation in sputtering. A molecular dynamics simulation of an atomic collision cascade is combined with a kinetic excitation model including electronic friction and electron promotion in close atomic collisions. The model is extended to account for potential excitation following the bombardment with a highly charged ion (HCI). The spatial spreading of the excitation generated in the cascade is treated in an diffusive approach. The excitation energy density profile obtained this way is parametrized via an effective electron temperature, which is then used to calculate the ionization probability of each sputtered atom in terms of a simple charge exchange model. The results obtained for the impact of a 5 keV Ag atom onto a solid silver surface show that the average ionization probability increases from 4.7×10^-4 for a neutral projectile to 5.4×10^-4 for a highly charged projectile ion with a total ionization energy of 576 eV.     

Fermi shuttle acceleration in atomic collisions: the case of ion induced electron emission

The “Fermi shuttle” acceleration of electrons in ion–atom collisions, i.e. multiple collision sequences of electrons bouncing off the projectile and target nuclei, can lead to the emission of very energetic electrons (i.e. with velocities higher than the binary encounter electrons). We performed measurements of the evolution of the Fermi shuttle electron yield with the induced perturbation and the target atomic number. The yield increases with the perturbation parameter (ratio of projectile charge and projectile velocity q/v_P), which was varied from q/v_P ≈ 0.2 (weak perturbation) to q/v_P ≈ 2 (strong perturbation). We also introduce a more realistic scaling parameter, which accounts for the re-bouncing of the electrons on target and projectile, and show that the yields increase as a function of this parameter. For a given projectile, the Fermi shuttle electron yield increases with the target atomic number. Furthermore, we show that the velocity distribution of the high-energy electrons is exponentially decreasing N(v)  exp(−nv) and exhibits the same evolution of the slope n with projectile velocity as in the case of Fermi accelerated deuterons.     

Wave packet evolution of the valence state of a hyperthermal sodium ion impinging on a copper surface

One electron transfer in hyperthermal energy collisions of Na⁺ ions with clean Cu(1 0 0) surfaces is studied using a wave-packet propagation algorithm based on a semi-empirical model potential. Three specific collision events are considered in which the Na particle comes out either reflecting off the surface or after multiple scattering processes within the target. The evolution operator, depending parametrically on the trajectories of the atoms leaving the sample, is discretized via a split approximation and a three-point differentiation scheme. In this way, the time-reversed state of the projectile is calculated and projected onto the initially filled states of the target to obtain the neutralization probability of the scattered atomic level. The calculations are consistent with literature values [8].