Electron Loss Cross Sections Research Articles

Charge exchange cross sections of carbon ions

Based on experimental data on the ion charge distributions, the cross sections of single electron loss σi, i + 1 and single electron capture σi, i − 1 by carbon ions with velocities (2.7–8) × 108 cm/s in different gaseous media (He, N2, and Ar) have been obtained. Regularities of the cross section variation of the electron capture and loss by carbon ions as a function of the ion velocity, ion charge, and atomic number of the target have been for the first time studied in a wide range of the initial ion charge, from i = 0 to i = 6. A qualitative agreement of the obtained results with the published data has been established for a number of other ions. Theoretical calculations of the cross sections of single electron loss by carbon ions in helium have been carried out.

Free-collision model calculations for the electron detachment of anions by noble gases

An extended version of the free-collision model was employed for the calculation of the electron detachment cross sections of several anions, with npi structures, i = 2, 3, 5 and 6, namely B−, Al−, C−, O−, S−, F− and Cl−, in collisions with noble gases in the intermediate-velocity regime. The calculations were performed only for the total electron detachment cross sections, except for the C− case, where partial electron-loss cross sections were obtained. Multiple electron loss was analysed within the independent particle model. The comparison of the calculated cross sections with the available experimental data shows good agreement in almost all cases.

Features of energy loss for ions with K vacancy

The change in the average charge of helium-like ions when metastable particles are present in the beam is studied. The charge fractions and average charges are calculated as functions of the target thickness for ions with Z = 3–8 at a velocity of 3.65 au. Previous data on the cross sections for electron capture and loss by metastable ions are used in the calculations. It is shown that, for all ions under consideration, the presence of metastable particles in the beam leads to an increase in the average equilibrium charge and, possibly, to a corresponding increase in energy loss and ion ranges.

Gas-solid difference in charge-changing cross sections for bare and H-like nickel ions at200MeV∕u

It is well known that the density of the target can have a crucial impact on charge-changing collisions of partially ionized heavy ions. However, the basic understanding of this experimental observation is hampered by the difficulty in knowing the charge-state evolution of projectiles inside solids. Therefore, the present experiments with $200\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕\mathrm{u}$ bare and H-like nickel ions were performed to study charge-changing cross sections in different monatomic and compound gases and solids. The experimental results clearly demonstrate that the electron-loss cross sections in solids increase by about 40% compared to gases. The results support the Bohr-Lindhard model which predicts this gas-solid difference originating from enhanced ionization of excited ions. The experimental results are compared with recent theoretical estimates.

Charge states of medium energy He ions scattered from single and poly-crystal surfaces

High-resolution medium energy ion scattering (MEIS) spectroscopy has unveiled fine structures of surfaces and interfaces. However, problematic issues arise due to its excellent energy resolution. In particular, when one uses He+ beams, the He+ fraction η+(1) for the scattering component from top-layer atoms is frequently non-equilibrated owing to short exit path length. This leads to significant uncertainties of the absolute amount of atoms located on top of a surface. To overcome this difficulty, it is essential to acquire reliable data of equilibrium and non-equilibrium charge fractions and also to model the charge exchange process based on a simple picture. In this paper, we analyze the MEIS spectra from single and poly crystals of Si, Ni and Cu together with c-axis oriented graphite and derive electron capture (σ10) and loss (σ01) cross sections dependent on emerging ion velocity. Here, we assume that a He ion when arrives at a Maffin-tin sphere after a large angle collision takes the He+ state and then undergoes many charge exchanging collisions with valence electrons until leaving an electronic surface. The velocity dependent σ10 and σ01 values derived well reproduce equilibrium and non-equilibrium charge fractions of He+ except for graphite and poly-crystal Si at relatively large emerging angles. Such a deviation comes from the markedly anisotropic distributions of the valence electrons of Si and graphite with strong covalent bonds.

Electron Loss Cross Sections for a Heavy Ion Beam Probe

Electron loss cross sections of Au+ and Au2+ by electron and proton impact are calculated by using respectively the Lotz formula and the LOSS and CAPTURE computer codes. The corresponding rate coefficients have also been calculated. Using this information, the signal levels of heavy ion beam probe in the Large Helical Device are estimated. The calculated beam currents at the detector position are compared with the detected beam currents in the MeV energy range for a plasma electron density of 1 × 1019 m-3 and electron temperature of 1.5 keV. The obtained cross section / rate coefficient data can also be used for reconstruction of electron density and temperature profiles.

Charge transfer and ionisation by intermediate-energy heavy ions

The use of heavy ion beams for microbeam studies of mammalian cell response leads to a need to better understand interaction cross sections for collisions of heavy ions with tissue constituents. For ion energies of a few MeV u(-1) or less, ions capture electrons from the media in which they travel and undergo subsequent interactions as partially 'dressed' ions. For example, 16 MeV fluorine ions have an equilibrium charge of 7(+), 32 MeV sulphur ions have an equilibrium charge of approximately 11(+), and as the ion energies decrease the equilibrium charge decreases dramatically. Data for interactions of partially dressed ions are extremely rare, making it difficult to estimate microscopic patterns of energy deposition leading to damage to cellular components. Such estimates, normally obtained by Monte Carlo track structure simulations, require a comprehensive database of differential and total ionisation cross sections as well as charge transfer cross sections. To provide information for track simulation, measurement of total ionisation cross sections have been initiated at East Carolina University using the recoil ion time-of-flight method that also yields cross sections for multiple ionisation processes and charge transfer cross sections; multiple ionisation is prevalent for heavy ion interactions. In addition, measurements of differential ionisation cross sections needed for Monte Carlo simulation of detailed event-by-event particle tracks are under way. Differential, total and multiple ionisation cross sections and electron capture and loss cross sections measured for C(+) ions with energies of 100 and 200 keV u(-1) are described.

Semiclassical treatment of excitation and electron loss inAq++H(1s)collisions using spherical Bessel functions

We perform monocentric close-coupling calculations to obtain partial and total cross sections for excitation and electron loss in bare ${A}^{q+}+\mathrm{H}(1s)$ collisions, with $1\ensuremath{\leqslant}q\ensuremath{\leqslant}6$, for intermediate $(E=40\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕\mathrm{amu})$ to high $(E=7000\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕\mathrm{amu})$ impact energies. We use underlying basis sets of even-tempered Slater-type orbitals and confined spherical Bessel functions and compare the accuracy of the cross sections derived from these two implementations. Scaling rules are then established for the partial excitation cross sections of interest in fusion plasma research. We also undertake impact parameter first-Born calculations using the spherical Bessel underlying set to compare in the course of collision the close-coupling and perturbative descriptions of the ionization process.

Dominant screening process in the projectile electron loss for F- + Ar collisions

A comparison between projectile electron loss cross sections for negative, F-, and positive, He+, projectiles is presented for collisions with Ar target. The behavior of the two collision systems is similar for the projectile electron loss with target ionization. For projectile electron loss without target ionization (the so-called screening electron-loss process), quite different situations are presented for the studied positive and negative projectiles. For He++ Ar, the loss without target ionization collision channel is negligible for intermediate-to-low energies. On the other hand, for F-+ Ar, this collision channel is the dominant one in the total projectile electron loss at intermediate-to-low velocities. The roles played by coupling with the electron capture by the projectile collision channel and by the very different binding energies for negative and positive projectiles are discussed.

Electron loss cross sections of fluorine negative-ion projectile for modeling of inertial confinement fusion

Negative ion beams have been proposed as drivers for inertial confinement fusion (ICF), as high-velocity neutral projectiles produced by photodetachment may efficiently impact and heat up a hydrogen pellet target. Charge-changing cross sections are henceforth needed to estimate the beam attenuation in the residual gases. In this work we analyse cross section measurements for the several electron-loss collision channels of fluorine anions impinging on argon (10-50 keV/u energy range) and producing charge states from Ar + to Ar 4+ . Cross sections for projectile destruction associated to target ionization rise steeply with velocity, displaying a clear energy threshold. This threshold is characteristic of a collision process involving direct interaction between a projectile electron and a target electron.

Projectile electron losses in the collisions with neutral targets: sudden-perturbation approximation

An approach based on the sudden-perturbation approximation is presented for the treatment of single and multiple electron losses of high and intermediate energy projectiles in their collisions with neutral targets. Using this approach, we calculate electron loss cross sections of hydrogen-like Pb81+ and Au78+ projectiles in the collisions with neutral atoms. Also, multiple electron loss cross sections are calculated for U10+ and U28+ projectiles in their collisions with N2 and Ar targets.

Formation of O 2+ in collisions between O + ions and N 2 molecules

We report measurements of the total and absolute differential electron loss cross sections of 2.0–5.0 keV O + ions in collisions by N 2 target at scattering angles between − 3.2 ° ≤ Θ ≤ 3.2 ° in the laboratory frame. The behavior of the absolute differential cross sections display an expected decreasing behavior with increasing angle. The measured total electron loss cross section show a monotonically increasing behavior as a function of the incident kinetic energy and found to be within the order of magnitude between 1 0 − 19 and 1 0 − 21 cm 2.

Charge-changing cross sections of fastH0,1+andHe0,1+,2+projectiles inC60

Electron capture and loss cross sections have been measured for fast light projectile ions of $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ ${\mathrm{H}}^{0,1+}$ and $0.5--2.0\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ $^{4}\mathrm{He}^{0,1+,2+}$ in collisions with ${\mathrm{C}}_{60}$. The gaseous target of ${\mathrm{C}}_{60}$ was prepared by heating ${\mathrm{C}}_{60}$ powder in a target cell to temperatures of $300--500\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, and outgoing charge fractions were measured as a function of the cell temperature. Absolute cross sections are deduced by using two different vapor-pressure data available in literature. Experimental cross sections are examined in comparison with theoretical values obtained from various conventional formulas proposed for atomic targets. In addition, single- and double-electron capture cross sections are also calculated on the basis of a classical model by taking account of the local electron density of ${\mathrm{C}}_{60}$. From a complete set of our experimental cross sections, equilibrium charge fractions are also deduced and found to be essentially the same as carbon-foil data, indicating no gas-solid difference.

Cross sections for charge-changing processes involving kilo-electron-volt H andH+with CO andCO2

Absolute differential cross sections are reported for electron capture and loss by 1-5 keV H atoms incident on CO and CO{sub 2} for laboratory scattering angles up to 1.73 deg., and for charge transfer of 1-5 keV H{sup +} with CO and CO{sub 2} for scattering angles up to 2.51 deg. To our knowledge, the H-atom differential electron-capture and -loss cross sections presented here are the first of their kind for CO and CO{sub 2}. The differential electron-loss cross sections are very similar to one another, and to previous measurements with other molecular targets, suggesting that some aspects of these collisions may be amenable to a relatively basic theoretical model. The differential measurements reported here significantly advance our knowledge of these collision processes and very good agreement is observed between the corresponding integral cross sections and prior work.

Electron stripping cross-sections for fast, low charge state uranium ions

Cross-sections for projectile electron loss for U 10+ and U 28+ colliding with H 2, N 2, and Ar were calculated using the n-body classical trajectory Monte-Carlo method. The calculations include electrons on both nuclear centers and all electron–electron and electron–nuclear interactions between centers. Multiple ionization is inherently included in these many-electron calculations. Overall, except for the H 2 target where the projectile stripping is overestimated by a factor of two, the calculated cross-sections are in reasonable accord with available data and the recent beam lifetime measurements from GSI-Darmstadt. For energies less than 100 MeV/u, the N 2 and Ar cross-sections do not scale as E −1.0 as predicted by one-electron theories.

Cross sections for electron capture and loss by keV oxygen atoms in collisions with CO and CO2

Interpretation of the energetic neutral atom data from the ASPERA‐3 instrument aboard the ESA Mars Express spacecraft requires knowledge of the relevant charge‐changing atomic collision cross sections. Important among these are collisions involving energetic O atoms, and absolute cross sections are reported here for electron capture and loss by 1–5 keV oxygen atoms incident on CO and CO2 for scattering angles between 0.02° and 1.73° in the laboratory frame. All of the differential cross sections are forward peaked, but those for electron loss decrease particularly slowly with scattering angle at low energies indicating that many of the colliding particles suffer significant deviation.

Energy loss calculations for fast light ions in celluloid including charge-exchange processes

A method is proposed to calculate the charge-exchange energy loss (−dE/dx)ex and electronic energy loss (−dE/dx)el on the basis of the electron capture and loss cross-sections, extracted from the experimental data. The experimental and calculated results are presented for energy loss of projectile ions Be, B, N and O with 0.35MeV/nucleon, passing through celluloid films. The dependence of energy loss on the initial charge of projectile ions and target thickness in nonequilibrium conditions is examined.

Projectile electron loss and capture in MeV/u collisions of U28+ with H2, N2 and Ar

Electron capture and loss cross sections for U28+ colliding with H2, N2 and Ar were measured at 3.5 and 6.5 MeV/u. These data were used to benchmark n-body calculations using the classical trajectory Monte Carlo method. The n-body calculations include electrons on both nuclear centres and all electron–electron and electron–nuclear interactions between each centre. For the U28+ ion, 36 electrons were incorporated in the calculations (4s24p64d104f145s25p2), while for the H, N and Ar targets all electrons were used except those for the K-shell of Ar, leading to 39-, 45- and 54-body calculations, respectively. Projectile electron loss was predicted for U28+ at energies from 2 to 150 MeV/u. Only for the H-target did the projectile electron loss cross section decrease approximately as E−1. The heavier targets exhibited slower energy dependences, contrary to the E−1 prediction of one-electron theories. Moreover, the collisional interactions are quite strong with an average of 1.64 and 2.88 electrons removed from the U28+ ion at 10 MeV/u in each collision with N and Ar, respectively. These data and calculations were used to assess the vacuum requirements for the SIS-100 synchrotron ring under construction at GSI-Darmstadt. For the residual gases expected to be in the ring, the U28+ lifetime was found to be essentially constant as a function of projectile energy, leading to very stringent vacuum requirements.

Cross sections for charge change in argon and equilibrium charge states of 3.5 MeV/amu uranium ions passing through argon and carbon targets

Cross sections for single and multiple electron capture and loss were measured for 3.5MeV/amu uranium ions, traveling in argon gas, as a function of incident charge state. Multiple electron loss in single collisions was found to contribute significantly to the total loss cross section. The measured cross sections were used to determine the average equilibrium charge in argon by three different methods. The resulting charges were in good agreement with each other and with the effective charge calculated from stopping powers. In order to investigate the gas–solid (density) effect on the average equilibrium charge, the charge distributions of 3.5MeV/amu uranium ions emerging from carbon foils of different thicknesses were measured. It was found that the average equilibrium charge of the uranium ions emerging from the solid is 41% larger than that of the uranium ions emerging from the gas. The energy dependences of the average equilibrium charges for uranium ions exiting carbon and argon targets were examined by combining the present results with previous results of other investigators and compared with the predictions of a semiempirical formula developed recently by Schiwietz and Grande.

Electron capture and loss by kilo-electron-volt oxygen atoms in collisions with He,H2,N2, andO2

Absolute differential cross sections are reported for electron capture and loss by (1-5)-keV oxygen atoms incident on He, H{sub 2}, N{sub 2}, and O{sub 2} for scattering angles between 0.02 deg. and 1.73 deg. in the laboratory frame. The form of the differential cross sections is seen to vary significantly with energy and between different targets. Differences between the present O-atom electron-loss cross sections and those for H atoms reported previously imply that the underlying physical mechanism may not be the same. The integral cross sections, also reported here, are consistent with most previous studies. The consensus of the available electron-loss data suggests that the cross sections of Fogel et al. [Soviet Phys. JETP 35, 601 (1959)] are in error.