Incident Particle Velocity Research Articles

Inner-shell alignment of atoms in ion-atom collisions. II. Electron capture

For pt.I see ibid., vol.13, p.1601 (1980). The alignment of ions with an inner-shell vacancy resulting from electron capture in ion-atom collisions is treated theoretically. The general expressions for the alignment are obtained in the Oppenheimer-Brinkman-Kramers and Born approximations. Simple analytical formulae for the alignment are derived within the framework of the hydrogenic model. The dependence of the degree of alignment on the incident particle velocity and the ratio of charges of the colliding particles is analysed. The alignment due to electron capture is shown to differ essentially from the alignment due to direct Coulomb ionisation. The sensitivity of the degree of alignment to the form of captured-electron wavefunctions and to the type of perturbing interaction is investigated. The experimental data on the angular distribution of Auger electrons in the ionisation of the 2p3/2subshell of Mg by protons and He+ ions are reanalysed taking into account the electron capture mechanism.

Electron transfer in keV-energyHe++4atomic collisions. I. Single and double electron transfer with He, Ar,H2, andN2

Single- and double-electron-transfer cross sections have been measured for a $^{4}\mathrm{He}^{++}$ beam incident on thin He, Ar, ${\mathrm{H}}_{2}$, and ${\mathrm{N}}_{2}$ gas targets over the energy range 15-125 keV. Comparison with previous $^{3}\mathrm{He}^{++}$ experimental results is made at the same incident particle velocity. For ${\mathrm{He}}^{++}$ collisions with He, we find good agreement with the theory for double electron transfer, but conclude that the single-electron-transfer cross section is far from being understood. Interpretation of the data in terms of simple theoretical ideas indicates that capture into excited states of the ${\mathrm{He}}^{+}$ ion can be the dominant single-electron-transfer process in some keV-energy ${\mathrm{He}}^{++}$ atomic collisions.

Combined theory of classical excitation of atoms by charged particles

A 'combined' analytic theory of classical excitation of hydrogenic atoms and ions by charged particles is presented: it is valid for all energy transfers at sufficiently high incident particle velocity. The theory reduces to the binary encounter or classical impulse approximation and to an adiabatic dipole perturbation theory in their respective ranges of validity. The combined theory agrees reasonably well with published Monte Carlo trajectory calculations. It is confirmed that adiabatic effects are a major defect of binary encounter theory. The energy transfer distribution for fixed impact parameter is studied.

Theoretical Investigations of Gas–Solid Interaction Phenomena. IV Spatial and Velocity Distributions

A study of the spatial and final velocity distributions for gaseous particles reflected from a solid surface is reported. The three-dimensional classical model previously used by the authors is employed to study the scattering distributions as functions of the incident particle velocity, the velocity distribution in the incident beam, and surface temperature. The broadness of the spatial scattering distributions is predicted to decrease with increasing incident velocity. The spatial distribution peak position is specular for large incident velocity, shifts toward the surface for intermediate velocity, and approaches the surface normal for small incident velocity. The model indicates that the spatial distribution dependence upon initial velocity causes velocity-selected and thermal beams to give similar spatial scattering. For hot surfaces the spatial scattering is indicated to be a rather insensitive function of surface temperature. The velocity distributions of reflected particles are predicted to be non-Maxwellian, bimodal for large incident velocities, and clearly different for velocity-selected and thermal incident beams. The results indicate that final velocity distribution measurements may be the most informative characteristic of gas–solid interaction phenomena.

Interaction of a Ring-Reinforced Shell and a Fluid Medium

This work is concerned with the transient dynamic response of a periodically ring-reinforced, infinitely long, circular cylindrical shell to a uniform pressure suddenly applied through the surrounding acoustic medium. The incident particle velocity is zero, and the rings are assumed to be slightly flexible. A classical theory of the Donnell type is used to analyze the shell while the fluid is described by the linear acoustic field equation. The solution is obtained by assuming a power series expansion in the ring stiffness parameter and utilizing a technique which reduces the transient dynamic problem to an equivalent steady-state formulation. Numerical results are presented for a steel shell immersed in salt water for different ring spacings. For the case of rigid rings, a cylindrical and plane wave approximation was also used to represent the fluid field. It is shown that the cylindrical wave approximation yields reasonably accurate results. Flexible ring results, although limited, indicate that undamped or nonradiating components of the shell vibration are activated.

Transient Response of a Periodically Supported Cylindrical Shell Immersed in a Fluid Medium

The dynamic response of a periodically simply supported, infinitely long, circular cylindrical shell to a pressure suddenly applied through the surrounding acoustic medium is investigated. The incident particle velocity is zero, and the pressure is assumed to have a harmonic spatial variation parallel to the shell axis. The exact solution is obtained by use of a Fourier integral transform, and the resulting inversion integral is evaluated by numerical and asymptotic integration. Two solutions to the same problem are obtained by using a plane and cylindrical wave approximation for the radiated field. The range of their applicability is investigated. For a steel shell in water ccs2=0.08815 it is found that, when the supports are placed three shell diameters apart, the use of the cylindrical wave approximation results in a 5-percent underestimation of the maximum deflection, while when the supports are placed one sixth of a shell diameter apart, the approximations are invalid.