Momentum Distribution Of Target Electrons Research Articles

N‐shell ionization cross sections by proton impact in the BEA

The N‐subshell ionizations cross sections of heavy elements by proton impact have been calculated in the binary‐encounter approximation. The momentum distribution of target electrons is taken into account by the use of the nonrelativistic and relativistic hydrogenic models and the Hartree–Fock–Roothaan and the relativistic Hartree–Fock–Roothaan methods. The obtained subshell ionization cross sections are compared with the experimental data and other theoretical calculations. The electronic relativistic effect and the wave‐function effect on N‐shell ionization cross sections are discussed.

M-X-ray production cross sections of heavy elements by charged-particle impact

The M-subshell ionization cross sections of heavy elements by proton and helium-ion impact have been calculated in the binary-encounter approximation. The momentum distribution of target electrons is taken into account by the use of the nonrelativistic and relativistic hydrogenic models and the Hartree–Fock–Roothaan method. The obtained subshell ionization cross sections are converted into the M-X-ray production cross sections and compared with experimental data and other theoretical calculations. The electronic relativistic effect and the wave-function effect on M-shell ionization cross sections are studied and possible reasons for large discrepancy between theory and experiment for Mγ-X-ray production cross section are discussed.

Kinetic electron emission by grazing atom scattering from clean flat metal surfaces

Kinetic electron emission (KE) for grazing scattering of H, He, Ne, and Ar ground state atoms with keV/amu impact energies on clean monocrystalline atomically flat Al and Cu surfaces has been studied in coincidence with projectile energy loss. Measured KE yields are subject to a clear impact energy threshold, in agreement with a free electron gas model description for the target electron momentum distribution (“classical” KE threshold). For smaller projectile scattering angles corresponding to larger distances of closest approach to the surface, this classical KE threshold is shifted to higher impact energies. By measuring KE threshold energies for different projectile scattering angles, we have probed the effective electron surface potential.For scattering of Ne and Ar atoms, a very weak electron emission is observed below the classical KE threshold, which within a more realistic description of the electron momentum distribution for the target surface can be ascribed to higher electron momenta.Grazing projectile scattering also permits a practically non-destructive surface structure determination, because a considerably larger number of electrons is emitted when changing from planar to axial surface scattering “surface triangulation”.

Dielectronic Recombination and Resonant Transfer Excitation for Ca19+ Ions

In the frame of quantum defect theory, the dielectronic recombination cross sections of Ca19+ ion are calculated by a simple relativistic configuration interaction method. Based on this calculation, the resonant transfer and excitation cross sections of Ca19+ with H2 and He targets are estimated in impulse approximation. The theoretical results for Ca19+ + H2 system are compared with the measurements available. The effect of target electron momentum distribution on the resonant transfer and excitation cross sections is discussed.

Electron transfer and projectile excitation in single collisions

Studies of electron transfer (capture) and projectile excitation occuring together in a single encounter are reviewed. This combined capture and excitation can result from either a correlated or an uncorrelated interaction. The correlated process is referred to as resonant transfer and excitation (RTE), while the uncorrelated process is called nonresonant transfer and excitation (NTE). RTE is analogous to dielectronic recombination (DR) which occurs in the interaction between an ion and a free electron. Experimental and theoretical works leading to establishing the existence of RTE are reviewed as well as considerations relevant to distinguishing RTE from NTE. The dependences of RTE on projectile atomic number (14≤ Z≤23) for Li-like ions, and on projectile charge state for H-like to Ne-like ions have been measured and compared with theory. The effect of the target electron momentum distribution on RTE has been demonstrated by comparing measurements for H 2 and He targets. Measurements of RTE involving L-shell excitation have been conducted and compared with K-shell results. All of the measured RTE cross sections to date for H 2 and He targets are in reasonable agreement with calculations based on theoretical DR cross sections averaged over the target electron momentum distribution; however, systematic discrepancies between experiment and theory exist. Additionally, it has been found that RTE can contribute considerably to total single-electron capture cross sections in the region where RTE is important, accounting for nearly half of the total capture events for calcium ions colliding with H 2.

K- and l-shell resonant transfer and excitation in ion-atom collisions

Recent experimental studies of resonant transfer and excitation (RTE) in ion-atom collisions are reviewed. In the RTE process correlated electron capture and projectile excitation occur together in a single encounter with a target atom. Measurements of Ca q+ + H 2 ( q= 10–19) from 100 to 370 MeV establish the projectile charge-state dependence of K-shell RTE and provide a detailed test of the theory. Structure due to RTE is observed in the energy dependence of the total electron-capture cross sections for this collision system. A comparison of the Ca 17++H 2 data with previous results for Ca 17++He demonstrates the effect of the target-electron momentum distribution on the RTE process. Studies of 230–610 MeV Nb 31+ +H 2 provide information about RTE involving projectile L-shell excitation. All the measurements are in reasonable agreement with theoretical calculations.

Resonant transfer and excitation: Dependence on projectile charge state and target-electron momentum distribution.

Resonant transfer and excitation: Dependence on projectile charge state and target-electron momentum distribution.

Model for radiative electron capture: an interpretation of the line width

Radiative electron capture (REC) X-ray profiles have been analysed for oxygen ions incident on a variety of gaseous targets. A model for REC is given which includes the effects of binding in both the target and projectile and the target electron momentum distribution. From measurements of the REC line widths the average kinetic energies of the outer-shell target electrons are obtained which are in good agreement with theoretical estimates.