Inner-shell Electron Capture Research Articles

Inner-shell electron capture by impact of positron on the multi-electron atomic targets

The first-order Coulomb-Born approximation has been applied to the study of positronium formation through K-shell electron capture in the collision of positron with multi-electron atomic targets. The single-zeta Roothaan-Hartree-Fock wave functions are used to describe the electron initial bound states. The differential and total cross sections are computed for the impact of positron on helium, carbon, neon, sodium and argon atoms, with the formation of positronium in its ground state. For helium atoms, the calculated total cross sections are compared with the available experimental data and other theoretical calculations. The comparison shows a good agreement between the present calculations and the measurements.

Charge exchange in collisions between heavy low-charged ions

The probabilities and the effective cross sections of collision-induced one-electron charge exchange between singly charged and four-charged heavy Xe, Cs, Ba, Pb, Bi, and U ions at energies E>0.1 keV/u are calculated by a method of multichannel normalization in the impact parameter representation. The cross sections are rather large with a maximum σm≈10−15 cm2 at relative energies E m ≈10–30 keV/u. For collision energies E 1 MeV/u, the charge exchange proceeds largely by the capture of inner shell electrons of the ionic targets. The charge exchange cross sections calculated for low-charged Xe, Cs, Ba, Pb, Bi, and U ions are compared with available theoretical and experimental data.

Multiple target ionization in collisions between highly charged ions and Ar

We have performed measurements on charge-state distributions of target ions produced in collisions of , , , , and on Ar. Charge states of Ar target ions higher than the initial projectile charge state are observed for , and . This intriguing observation seems to imply that even in low-energy collisions () of highly charged ions on gas targets excitation of the target occurs due to inner-shell electron capture. For collisions of and on Ar less than six electrons are transferred.

Relativistic continuum distorted wave theory for electron capture

A new relativistic continuum distorted wave model is presented. A first-order scattering amplitude for inner-shell electron capture is calculated, and the complete analytic form of the transition amplitude is obtained. Results for differential and total cross sections are presented for transitions with and without change of spin. Comparison with experimental data and other theoretical models is made. Agreement with experiment for total cross sections is good. Inconsistencies in the matrix distorted wave model are highlighted, and the correct form of the residual interaction is given for the first time. The utility of approximate relativistic wavefunctions are discussed, and a number of misunderstandings concerning their use in collision theory addressed.

The capture of inner-shell electrons in the strong-potential born (SPB) approximation

For the first time the capture of inner-shell electrons by protons is calculated by the SPB method without further approximation and using Hartree-Slater wavefunctions. The resulting cross-section has roughly the correct shape, but is much too large. The problem is traced to a loss of normalization caused by the SPB approximation. A suitably renormalized SPB gives close agreement with experiment.

Target continuum distorted-wave theory for capture of inner-shell electrons by fully stripped ions

The target continuum distorted wave (TCDW) theory is derived and developed. It describes charge exchange in asymmetric collisions, in particular the collision of a projectile ion of low charge with a target ion of high charge. The final state is represented by a TCDW function. The initial state is taken as a travelling atomic orbital, while the intermediate states are represented by a Coulomb-Green function. The theory is applied to capture by protons from the inner shells of heavy atoms. For s-s transitions, it is found that within a standard on-shell full-peaking approximation the second-order amplitude does not contribute. The total cross section for K-K electron capture in proton-carbon, neon and argon atom collisions is calculated in the energy range corresponding to values of ZT/v from 0.5 to 3.0, where ZT is the nuclear charge of the target and v the velocity of impact in atomic units. Agreement with experiment is excellent in all three cases and the cross section values compare extremely favourably with those of the well known strong-potential Born theory.

Charge state distributions for ions moving in metals

Charge transport processes for ions moving in metals have been analyzed. Three mechanisms are relevant: Auger, whereby an electron is captured or lost by the ion creating an electronic excitation in the solid; resonant processes, coherently induced by the potential of the ionic nuclei; and direct capture of inner shell electrons stemming from the target atoms. Atomic-like processes acquire increasing importance for higher ion velocity, v, and ion atomic number, Z. Charge state distributions for ion beams have been calculated in the range v/ Z ∼ 1–3 a.u., where no more than two electrons are involved. The results have been applied to ions B, C, N and O moving in Ai. Good agreement with available experimental evidence has been found.

Contributions from off-energy-shell states to inner-shell electron capture.

It is shown that contributions from off-energy-shell intermediate states are small for inner-shell electron capture in highly asymmetric ion-atom collisions. We analyze the influence of the on-energy-shell discontinuities of the electron wave function by introducing a cut-off Coulomb potential. We found that these discontinuities, which are mainly responsible for large corrections introduced by the strong-potential Born approximation, do not have physical meaning.

Response to "Contributions from off-energy-shell states to inner-shell electron capture"

We show that the off-shell factor is essential for a consistent description of electron capture even when effects of screening are incorporated as in the approximate description of Barrachina, Garibotti, and Miraglia.

Inner-Shell Electron Capture by a Swift Bare Ion: Second Born Effects

The second Born cross section for electron capture from a hydrogenlike atom of atomic number Z/sub T/ by a bare ion of atomic number Z/sub P/ and speed ..nu.. is evaluated for (Z/sub p/e/sup 2//h..nu..) very-much-less-than 1 and Z/sub T/ arbitrary. The ratio of the second to first Born cross sections increases rapidly as Z/sub T/ increases; for (Z/sub T/e/sup 2//h..nu..) > or approx. =1 this ratio is very large. These results indicate that second- and higher-order Born terms must be considered in calculating the cross section for inner-shell electron capture (or the time-reversed process).