V. P. Shevelko

Target density effects in collisions of fast ions with solid targets

The influence of the target density on the charge-changing—ionization and electron capture—cross sections when fast ions penetrate through solid targets is considered. It is shown that, with the target density increasing, electron-capture cross sections decrease and ionization cross sections increase, resulting in a higher mean charge of exit ions after a solid target compared to a gas target (often called gas-solid or density effects).Recent experimental data on equilibrium charge-state fractions F∞q of 6.0 MeV u−1 ions with atomic numbers Z = 6–26 passing through carbon foils [10, 11] are described in terms of the calculated charge-changing cross sections using a four-charge state model. It is found that the reasonable agreement can be obtained provided the target-density effects are properly accounted for. Moreover, the present treatment allows one, for the first time, to estimate the distributions of the exit ions over excited nl states from experimental equilibrium charge-state fractions using the charge-changing cross sections calculated with the density effects included; here n and l denote the principal and orbital quantum numbers, respectively.Numerical calculations of the charge-changing cross sections and equilibrium charge-state fractions of exit ions are performed for 6.0 MeV u−1 C2+, Ne4+, Mg5+, Si5+, Ar8+ and Fe9+ ions penetrating through carbon foils. Taking the target-density effects into consideration and comparing the calculated equilibrium charge fractions with the recently observed data for carbon foils, the nl distributions of exit ions with the largest fractions are estimated by fitting the calculated F∞q values to the experimental ones.

Ionization of heavy ions in relativistic collisions with neutral atoms

The problem of ionization of ions in ion-ion and ion-neutral relativistic collisions is considered. Formulas for ionization cross sections are derived in the Born approximation in terms of the momentum transfer without allowance for magnetic interactions. Using these formulas implemented in the LOSS-R code, the ionization cross sections are calculated for the K shells of neutral atoms colliding with protons and also for 1s and 2p electrons of multiply charged heavy ions (nuclear charge Z = 80−90) colliding with bare nuclei and neutral atoms. The calculation results are compared with experimental data and calculations of other authors.

Ionization of heavy ions in collisions with neutral atoms at relativistic energies

Ionization processes of heavy ions colliding with atoms and ions at relativistic energies are considered. Formulaes for calculating ionization cross sections in the Born approximation using momentum-transfer representation without regard to magnetic interactions are given as well as those in dipole and impulse approximations. Using the LOSS-R [25] and HERION codes, calculations of relativistic cross sections are performed for H-like multiply changed ions with the nuclear charge Z ≈ 80−90, colliding with neutral atoms and for multiply changed uranium ions colliding with protons and carbon atoms. The results of calculations are compared with available experimental data and calculations performed by other authors.

Influence of relativistic effects on electron-loss cross sections of heavy and superheavy ions colliding with neutral atoms

The influence of relativistic effects, such as relativistic interaction and relativistic wave functions, on the electron-loss cross sections of heavy and superheavy atoms and ions (atomic number Z ≳ 92) colliding with neutral atoms is investigated using a newly created RICODE-M computer program. It is found that the use of relativistic wave functions changes the electron-loss cross section values by about 20–30% around the cross-section maximum compared to those calculated with nonrelativistic wave functions. At relativistic energies E ≥ 200 MeV/u, the relativistic interaction between colliding particles leads to a quasiconstant behavior of the loss cross sections σELrel ∼ const, to be compared with the Born asymptotic law σELB ∼ lnE/E.

Influence of the isotope effect on the charge exchange in slow collisions of Li, Be, and C ions with H, D, and T

The influence of the isotope effect (mass dependence) on the charge-exchange process in low-energy collisions of light ions with hydrogen isotopes (H, D, and T) is studied using the adiabatic theory of transitions in slow collisions developed by E. Solovev [Sov. Phys. Usp. 32, 228 (1989)]. Results of the numerical calculations are presented for the charge-exchange probabilities and cross sections of Li, Be, and C ions colliding with hydrogen isotopes and for the inverse reactions.

Electron loss of heavy many-electron ions in relativistic collisions with neutral atoms

Electron-loss processes arising in collisions of heavy many-electron ions (like U28+) with neutral atoms (H, N, Ar) are considered over a wide energy range including relativistic energies. Various computer codes (LOSS, LOSS-R, HERION, and RICODE), created for calculation of the electron-loss cross sections, and their capability are described. Recommended data on the electron-loss cross sections of U28+ ions colliding with H, N, Ar targets and predicted lifetimes of U28+ ion beams in accelerator are given. Calculated electronloss cross sections are compared with available experimental data and other calculations.

Effect of the target density on the cross section of charge exchange between fast ions and atoms

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Collision processes involving heavy many-electron ions interacting with neutral atoms

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