Asymptotics of the cross section for the electron loss by atoms and ions in light media

The dependence of the cross section of electron loss on the nuclear charge Z of a bombarding ion 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 show that the cross section of electron loss for fast collisions increases monotonically as Z and Z _t increase, which can be used to interpolate cross sections for the processes for which there are no experimental data.     

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.     

Peculiarities in charge symmetry of energy loss in ion-atom collisions

Systematic experimental studies on energy loss (?dE/dx) were performed for ions with nuclear charge Z = 2–18 in various gases. The energy range ～0.001 to ～1 MeV/amu was considered. Detailed analysis confirmed the oscillating character of the energy loss dependence on the ionic nuclear charge associated with the ions’ electron shell structure. The symmetry of the energy loss dependence on the nuclear charges of projectile Z and target Z _t is examined.     

Description of single-electron capture by fast multielectron ions

An analytical approximation of wave functions has been derived for the excited states of atoms and ions. The nuclear charge and the number of electrons are Z ≤ 10 and N _e ≤ 10, respectively. It is shown that the cross section of electron capture by fast ions must be estimated with allowance for their Coulomb interactions. The theoretical dependence between the single-electron capture cross section and the collision energy is close to the experimental, when ion interactions in the final state are taken into account. This proximity enables us to analyze the correlation between theoretical and experimental results.     

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)     

Ionization of K-shell electrons by electron impact

We have investigated the universal scaling behavior for cross sections of the single K-shell ionization by electron impact. The calculations are performed within the framework of non-relativistic perturbation theory, taking into account the one-photon exchange diagrams. Special emphasis is laid on the near-threshold energy domain. The results obtained are applicable for wide family of atomic targets with moderate values of the nuclear charge Z.     

Simple model for the ionization of helium atoms by fully and partially stripped ions in the strong interaction region

Theoretical calculations employing the modified over-barrier model to investigate single and double ionization cross sections of helium in collisions with highly charged ions are presented in the strong perturbation region. It shows the velocity and charge state dependences of cross sections, which coincides with the available experimental data. In order to determine the reliability of this model for partially stripped projectiles, the cross-section ratios have been measured for CZp+, OZp+-He (Zp=1-4) by the coincidence technique in the velocity range of 1-4.5 a.u. The calculated results are approximately in agreement with the experimental data.     

K-shell ionization of atoms and ions by relativistic projectiles

We evaluate the total cross section for the single K-shell ionization of atoms and ions by the impact of relativistic electrons. The study is performed to leading orders of the QED perturbation theory with respect to the parameters αZ and 1/Z. The results obtained are in good agreement with experimental data for different atomic targets. In the case of moderate values of the nuclear charge Z, the total cross section is described by a simple analytic formula. The K-shell ionization by relativistic heavy particles is also considered.     

Double <Emphasis Type="Italic">K</Emphasis>-shell ionization of atoms by a single photon

We investigate the double K-shell ionization of heliumlike ions by a single photon. A fast convergence of QED perturbation theory with respect to the parameter 1/Z is demonstrated in the entire nonrelativistic domain for moderate nuclear charge numbers Z≥2. The ratio of double-to-single photoionization cross sections is calculated for light heliumlike ions, taking into account the leading orders of 1/Z and αZ expansions. A comparison of our results with the available experimental data for a number of neutral atoms is presented.     

Effect of the structure of the singly charged ion on the cross section for electron capture

The calculations of the cross section for single-electron capture by fast ions are carried out in the Oppenheimer-Brinkman-Kramers approximation. The dependences of the experimental and calculated cross sections for single-electron capture by fast singly charged ions on the collision energy coincide. This makes it possible to estimate the cross section for electron capture in the case of ion-atom collisions if experimental data are absent. The results of calculations for projectiles with filled s-type subshells show that the contribution of electron capture channels to the excited state of the scattered particle depends on the collision energy.     

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.     

The reactions of 12C with 12C AT 293 MeV

Energy spectra, angular distributions, and elemental yield distributions have been measured for products Z = 1?9 produced in the reactions of ¹²C on ¹²C. A total reaction cross section 1170_?100⁺¹⁷⁰ mb was determined from the measured elemental cross sections and the principle of charge conservation. This total reaction cross section is about 250 mb less than the geometric cross section and agrees with the Glauber-model calculations of DeVries and Peng. The experimental energy spectra, angular distributions, and yield distributions were compared with those from model calculations for the statistical decay of the products of fusion and of incomplete fusion reactions. For both types of calculations, a modified version of the code LILITA was used. By comparing the data to model calculations, an upper limit of 75 mb for the fusion cross section was determined. That limit corresponds to an upper limit of L_crit for fusion of 10? in the sharp-cutoff approximation. The dominant reaction mechanisms appear to be incomplete fusion processes.     

Energy loss of light ions with allowance for the presence of metastable particles in the ion beam

The change in the average ion charge due to the presence of particles in metastable states in beams of helium-like ions has been studied. The charge distributions and average charges have been calculated for ions with nuclear charges Z = 3?7 and a velocity of 3.65 au in nitrogen. The previously obtained data on the cross sections of loss and capture of electrons by metastable ions and ions in the ground state were used in the calculations. It is shown that the presence of metastable particles in ion beams leads to an increase in the average charge and energy loss for all considered ions.     

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.     

Microscopic multichannel investigation of the <Superscript>6</Superscript>Li + <Emphasis Type="Italic">n</Emphasis> seven-nucleon nuclear system at low energies

The ⁶Li + n seven-nucleon nuclear system is studied at low energies within a microscopic approach based on the multichannel algebraic version of the resonating group model. The partial and total cross sections for the ⁶Li(n, t)⁴He reaction are calculated. The contributions of the various partial cross sections to the energy dependence of the total cross section are considered. The results of the calculations are found to be in a good agreement with experimental data.     

Effect of density on the equilibrium charge distribution of carbon and oxygen ions

Theoretical estimation of the equilibrium charge distribution of carbon and oxygen ions passed through a matter is obtained. The coefficient considering the effect of density on the charge distribution of these ions is calculated for an amorphous medium consisting of atoms with the nuclear charge Z _t (Z _t ≤ 54). An oscillating dependence of the average ion charge on the nuclear charge of the target atom is obtained which cannot be described by empirical relations.     

Spectroscopic constants of VUV laser transitions in ions of the palladium isoelectronic sequence

Spectroscopic characteristics of ions of the palladium isoelectronic sequence with nuclear charge Z=50–63 are theoretically studied. The Pd-like scheme of x-ray lasers is one of the most efficient schemes. Optical transitions promising for the development of lasers operating in the vacuum ultraviolet region are determined. The wavelengths and probabilities of these radiative transitions are presented, along with their cross sections and the rates of electron-impact excitation of the active levels. The results obtained are compared with experimental data and calculations available in the literature.     

Direct production of muon pairs by high-energy muons

For ultrarelativistic muons, the cross section for the process μ+Z→μ+Z+μ⁺+μ^? is calculated with allowance for the nuclear and atomic form factors. It is shown that the nuclear form factor affects significantly the cross-section value. The transverse-momentum distribution of muons is calculated. An approximate formula determining the total cross section to within 2 to 3% is derived. The fluxes of groups of cosmic-ray muons generated by the above process are estimated at various depths. It is shown that calculations performed earlier overestimate significantly the fluxes of such groups.     

Single electron capture in collisions of N^q＋ （q = 5, 6, 7） ions with helium

Close-coupling calculations are carried out for cross sections of the single electron capture in collisions of N^q+ (q = 5, 6, 7) ions with helium atoms in the collision velocity range from 0.3 a.u. to 1.8 a.u. The relative importances of the single ionization (SI) to the single capture (SC) are investigated for the N^q+ (q = 5, 6, 7) projectiles, respectively. The SI/SC cross section ratio for the N⁷⁺ projectile obtained from our calculations is in excellent agreement with the experimental data. The ratio curves also show us distinct behaviours when the charge of the projectile is different. The partial electron capture cross sections for different projectiles indicate that the electron on the target He atom tends to be captured by the projectile into its lower orbital of the outer shell with the decreasing projectile charge.     

The four-momentum transfer distribution for the deuteron break up at 3.3 GeV/c incident deuteron momentum

The differential cross section (dσ/dt) for the dp → ppn charge retention reaction at 3.3 GeV/c deuteron momentum is studied and compared with the Glauber multiple scattering theory. Within the limits of the uncertainties of the existing elementary nucleon-nucleon data, the simple Glauber model calculations give, in general, a fair agreement with experiment, except for the low |t| region where possible spin effects may play a role.