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

The electron-loss cross sections σ _{i, i + 1} and the electron-capture cross sections σ _{i, 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 σ _{i, i + 1} = σ _{i, i ? 1} or σ _{i, i ? 1} = σ _{i ? 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.     

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 σ _EL ^rel ～ const, to be compared with the Born asymptotic law σ _EL ^B ～ lnE/E.     

Investigation of cross sections for the formation and destruction of negative boron ions

The electron loss and electron capture cross sections σ _i,i+m and σ _i,i−m for boron ions and atoms traveling at the velocities V=1.19 and 1.83 a.u. in H₂, He, N₂, Ne, Ar, and Xe are measured. The known experimental data on these cross sections at velocities near the cross-section maximum are analyzed. It is found that the electron loss cross sections can be described by a formula which was previously derived in the free-collision approximation and takes into account features of both the ions and the ambient atoms. As the nuclear charge Z _t of the ambient atoms increases, the cross sections vary nonmonotonically, increasing on average as Zt _t ^1/2 . A formula based on the model of independent electrons is proposed for electron capture by ions with small values of the charge i. It describes the dependence of the electron capture cross section σ _i,i−1 on the mean binding energy of an electron in an ion with the charge i−1. The total electron capture cross section σ _i,i−1 is proportional to the number of vacancies in the unfilled electron shell nearest the nucleus. The cross sections 0σ _i,i−1 exhibit substantially nonmonotonic variation with Z _t, increasing on average as Z _t ^1/3 . Zh. éksp. Teor. Fiz. 116, 1539–1550 (November 1999)     

Fragmentation cross sections of relativistic 208Pb projectiles

Production cross sections of more than 270 isotopes ranging from Z = 59 to Z = 82 were measured in the reaction ²⁰⁸Pb(1 GeV A)+Cu. The method of identifying the projectile fragments and evaluating the production cross sections is described. The experimental data are compared with a modern version of the abrasion-ablation model and with the empirical parameterization EPAX. Apart from deviations in the details they both show an overall good agreement. The cross sections of those fragments which are produced by the removal of protons only test the lower part of the excitation energy distribution. For the first time, the four-proton removal channel could be observed.     

Modified over-barrier model for ionization cross sections of atomic hydrogen by multiply charged ions

The impact ionization of atomic hydrogen in collisions with H⁺, He²⁺, Li2,3+, C2,3,4,5,6+, N2,3,4,5+, O2,3,4,5,6+, and Ar3,4,5,6+ ions has been studied by the modified over-barrier model at low-to-intermediate velocities. Compared with the calculated results of the classical trajectory Monte Carlo (CTMC) method and the unitarized-distorted-wave approximation (UDWA), this model satisfactorily reproduces the experimentally obtained velocity dependence of the absolute ionization cross sections at intermediate impact velocities.     

Transport cross sections for excited muonic hydrogen

Transport cross sections for scattering of excited muonic hydrogen on hydrogen are calculated in the quasi-classic approximation in the energy range 0.01–50 eV.     

Determination of mean collision cross sections of free radical OH with foreign gases

Experimental studies of absorption by the free radical OH in the 13.4 GHz region (2Π^{$\text{3}\text{2}$} state, J = $\text{7}\text{2}$) have been used to determine collision cross sections of OH with foreign gases. We have performed both direct measurements of linewidths and measurements of absorption saturation over wide pressure ranges. The experimental values are compared with available theoretical values.     

Coulomb and photo cross sections for nucleon emission from relativistic O projectiles

Coulomb cross sections for nucleon emission out of ¹⁶O projectiles scattered with laboratory energies of 2.1, 60 and 200 GeV/nucleon on various target nuclei are calculated in first-order perturbation theory by using the corresponding photo cross sections. The photo cross sections are obtained with an 1-particle-1-hole basis in the giant resonance region and with the quasi-deuteron model up to photon energies of 140 MeV. Whereas the 2.1 GeV/nucleon results agree well with the experimental data points, the 60 and 200 GeV/nucleon cross sections are roughly one quarter lower than the measured ones, because also photons with energies higher than 140 MeV contribute at these incident energies.     

Differential cross sections for muonic hydrogen scattering on hydrogen molecules

The results of first calculations of the differential cross sections for muonic hydrogen scattering on hydrogen molecules are presented. They are functions of the initial and final kinetic energy of the system and the scattering angle. These calculations are based on the respective set of cross sections for muonic hydrogen scattering on hydrogen nuclei, obtained within the framework of the adiabatic method. The Fermi pseudopotential method is used to estimate the molecular binding effects. The influence of electrons on the cross sections under consideration is described in terms of the effective screening potential. Rotational and vibrational transitions are taken into account. The calculated molecular differential cross sections show a strong angular dependence. This effect is very significant for the electronic contributions to the cross sections, e.g. for collision energies above approximately 0.1 eV only the cross sections of small scattering angles are influenced considerably by the screening. Since these differential cross sections give detailed information about the final energies and complicated angular distributions of the scattered muonic atoms they are the proper basis for calculations concerning the deceleration of muonic hydrogen atoms in molecular hydrogen targets and for Monte Carlo simulations of different experiments in muonic physics.     

Next-to-leading order jet cross sections in polarized hadronic collisions

We present a next-to-leading order computation in QCD of one-jet and two-jet cross sections in polarized hadronic collisions. Our results are obtained in the framework of a general formalism that deals with soft and collinear singularities using the subtraction method. We construct a Monte Carlo programme that generates events at the partonic level. We use this code to give phenomenological predictions for pp collisions at √S = 500 GeV, relevant for the spin physics programme at RHIC. The possibility of using jet data to constrain the poorly known polarized parton densities is examined.     

Charge exchange cross sections of carbon ions

Based on experimental data on the ion charge distributions, the cross sections of single electron loss σ _{i, i + 1} and single electron capture σ _{i, 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.     

Excitation-autoionization cross sections and rate coefficients for Ga-like ions

Detailed level-by-level calculations of cross sections and rate coefficients for electron impact direct and indirect ionization of ions belonging to the GaI isoelectronic sequence (ground 3d ¹⁰4s ²4p) have been performed. The cross sections are presented in the energy range near the threshold for the five ions Kr⁵⁺, Mo¹¹⁺, Xe²³⁺, Pr²⁸⁺ and Dy³⁵⁺. The rate coefficients are given for ions from Kr⁵⁺ to U⁶¹⁺ in the GaI sequence at seven electron temperatures (kT _e = 0.1E _I , 0.3E _I , 0.5E _I , 0.7E _I ,E _I , 2E _I and 10E _I , where E _I is the first ionization energy). The calculations include the contribution of direct ionization (DI) calculated using the Lotz formula approximation and the contributions of excitation-autoionization (EA) computed in the framework of the distorted wave (DW) approximation for the 4s-nl, 3d-nl and 3p-nl resonant inner-shell excitations. The ionization enhancement due to the EA channels is presented as a function of Z along the GaI isoelectronic sequence. The present results show the great importance of the EA processes; an ionization enhancement factor of up to 10 is predicted for instance for La²⁶⁺ (Z = 57) at electron temperature of coronal equilibrium maximum abundance.     

Angular characteristics of processes of electron detachment from negative ions and hydrogen atoms in gases

The results of experimental measurement of spatial-angular distributions of hydrogen particles (H⁻, H⁰, H⁺) obtained in scattering of a collimated ribbon beam of H⁻ ions and H⁰(1s) atoms in He, Ar, Kr, Xe, H₂, O₂, and CO₂ gas targets for certain values of energy in the range from 0.6 to 15 MeV are reported. The experimental setup and the measurement procedure with an angular resolution of 5×10⁻⁶ rad are described. The angular characteristics of measured distributions, i.e., full width at half maximum and standard deviation, were determined. It is shown that the shape of distribution for a beam of hydrogen atoms produced by neutralization of H⁻ ions in a gas target varies with the type and thickness of the target, and the angular spread is smallest for the H₂ target. The variations in the shape of distribution are due to the contribution of scattering processes without changing the charge of particles.     

Spin-flip cross sections in muonic hydrogen scattering on hydrogen molecules

The results of calculations of the total cross sections of spin-flip processes in low energy muonic hydrogen scattering on hydrogen molecules are presented. These calculations are based on the respective set of cross sections for muonic hydrogen scattering on hydrogen nuclei, obtained within the framework of the multichannel adiabatic method. All combinations of the three hydrogen isotopes are considered. Molecular binding effects are described in terms of the Fermi pseudopotential method. Electron screening effects are calculated in the distorted wave Born approximation. Rotational and vibrational transitions of the molecules, due to collisions with muonic hydrogen atoms, are taken into account. The molecular and electron screening corrections do not exceed a few tens per cent for lowest collision energies.     

Electron-impact ionization cross sections and rates for ions of argon

A distorted-wave Born exchange (DWBE) approximation including relativistic correction is used to calculate the electron-impact ionization cross sections and rate coefficients for the highly charged ions Ar⁷⁺,…,Ar¹⁷⁺. The comparison of the calculated results with the experimental data and other theoretical calculations shows that the DWBE method is valid for these ions of argon. The calculated results for direct ionization cross sections and excitation autoionization were fitted by empirical formulas to meet the requirements of applications. A set of improved empirical formulas are used for the fast and accurate calculations of rate coefficients from the fit parameters of cross sections.     

State-selective radiative recombination cross sections of argon ions

The n-, (n,l)- and fine-structure level state-selective radiative recombinations (RR) cross sections of argon ions Ar¹⁸⁺,Ar¹³⁺,Ar⁷⁺ and Ar⁺ are obtained with the semi-classical Kramer formula, the relativistic self-consistent field (RSCF) method and the relativistic configuration interaction (RCI) method. It is found that for the highly charged ions with few electrons, the cross sections calculated with these three methods are in good agreement with each other. But as the number of electrons increases, the Kramer formula deviates from the RSCF and RCI results. For instance, when the energy of the incident electron is larger than 100 eV, the n-state selective cross sections of Ar⁷⁺ calculated from the Kramer formula are underestimated for more than 50%. The RSCF results are in general agreement with the RCI results. However, for the low charged ions, a clear distinction appears due to the strong configuration interaction, especially near the Cooper minimum. The n-resolved (n≤10) and total Maxwellian averaged rate coefficients are calculated, and the analytic fitting parameters are also provided.     

Optical potential ambiguities and fusion cross sections for heavy ions

We explore some of the effects of optical-potential ambiguities on the fusion cross sections for heavy-ion collisions, especially at energies below the top of the Coulomb barrier when the barrier-penetration model is used. Ambiguities of the Igo type in the real potential are found to have little effect except when the potential is very shallow. The cross sections are seen to be very sensitive to the imaginary potential adopted if this allows for some absorption within the barrier; both the magnitude and shape of the excitation function may be changed.     

Photoelectric cross sections for ions scaled from their neutral atoms

Removal of outer electrons from an atom does not significantly change the potential and wave functions over the region where the wave function of the remaining bound electrons is large. This explains why the partial cross sections of an ion are similar to those of its neutral atom but truncated at the ion's threshold. Scaling by the wave-function-effective-Z can significantly improve the accuracy of the ion partial cross sections.