2,063 research outputs found
Calibration of distorted wave Born approximation for electron impact excitation of Ne and Ar at incident energies below 100 eV
We calibrate the distorted wave Born approximation (DWBA) for electron impact
excitation processes empirically. Differential cross sections (DCS) for the
excitation of the , ,, and configurations of
Ne and the and configurations of Ar by electron impact are
calculated using DWBA for incident energies between 20 and 100 eV. The
calculated results are compared with the absolute experimental measurements and
other theoretical results. We found that the structure of the DCS can be well
reproduced by the DWBA model while the magnitude is overestimated for most
cases considered here. The differences in magnitude between DWBA and experiment
are used to test the calibration of DWBA such that the DWBA can be used to
describe laser-induced electron impact excitation processes. These processes
are involved in the non-sequential double ionization of atoms in strong laser
fields.Comment: 10 pages, 8 figure
Perturbative and Nonperturbative Calculations of Electron-Hydrogen Ionization
We compare calculations of the fully differential cross section for ionization of atomic hydrogen by electron impact using two different theories-the perturbative CDW-EIS (continuum distorted wave with eikonal initial state) approximation and the nonperturbative ECS (exterior complex scaling) method. For this comparison, we chose an impact energy of 54.4 eV, since this is near the lowest energy that our perturbative approach would be applicable and near the highest energy that can be tackled by the ECS method with our present computational resources. For the case of equal-energy outgoing electrons investigated here, the two theories predict nearly identical results except that CDW-EIS underestimates the ECS values nearly uniformly by about 30%. Interestingly, when initial-state projectile-target interactions are neglected by replacing the eikonal initial state with the unperturbed initial state (the approximation of Brauner, Briggs, and Klar @J. Phys. B 22, (2265) (1989:]). the cross section oscillates by ±50% about the ECS values
Theoretical and experimental(e,2e)study of electron-impact ionization of laser-aligned Mg atoms
We have performed calculations of the fully differential cross sections for electron impact ionization of magnesium atoms. Three theoretical approximations, the time dependent close coupling (TDCC), the three body distorted wave (3DW), and the Distorted Wave Born Approximation (DWBA), are compared with experiment in this article. Results will be shown for ionization of the 3s ground state of Mg for both asymmetric and symmetric coplanar geometries. Results will also be shown for ionization of the 3p state which has been excited by a linearly-polarized laser which produces a charge cloud aligned perpendicular to the laser beam direction and parallel to the linear polarization. Theoretical and experimental results will be compared for several different alignment angles, both in the scattering plane as well as in the plane perpendicular to the incident beam direction
Three-Dimensional Imaging of Atomic Four-Body Processes
To understand the physical processes that occur in nature we need to obtain a solid concept about the 'fundamental' forces acting between pairs of elementary particles. It is also necessary to describe the temporal and spatial evolution of many mutually interacting particles under the influence of these forces. This latter step, known as the few-body problem, remains an important unsolved problem in physics. Experiments involving atomic collisions represent a useful testing ground for studying the few-body problem. For the single ionization of a helium atom by charged particle impact, kinematically complete experiments have been performed since 1969 (ref. 7). The theoretical analysis of such experiments was thought to yield a complete picture of the basic features of the collision process, at least for large collision energies. These conclusions are, however, almost exclusively based on studies of restricted electron-emission geometries. Here, we report three-dimensional images of the complete electron emission pattern for the single ionization of helium by the impact of C6+ ions of energy 100 MeV per a.m.u. (a four-body system) and observe features that have not been predicted by any published theoretical model. We propose a higher-order ionization mechanism, involving the interaction between the projectile and the target nucleus, to explain these features
Fine-structure effect for (e,2e) collisions
For the case of inelastic electron-atom scattering, it has been known for some time that significant spin effects may be observed even if spin-dependent forces on the projectile can be ignored. These spin effects result from the Pauli principle and this phenomenon has become known as the fine-structure effect. Recently, the question of whether or not these same types of effects should be observed for atomic ionization has been considered and the initial indications are that significant spin asymmetries can also be expected for atomic ionization if the final ion satisfies LS coupling and the final J state of the ion can be resolved. In this paper, we consider this problem for electron-impact ionization of inert gases. The theory of the fine-structure effect is presented for ionization and first-order distorted-wave results are compared with very recent experimental data
Creation of a monopole in a spinor condensate
We propose a method to create a monopole structure in a spin-1 spinor
condensate by applying the basic methods used to create vortices and solitons
experimentally in single-component condensates. We show, however, that by using
a two-component structure for a monopole, we can simplify our proposed
experimental approach and apply it also to ferromagnetic spinor condensates. We
also discuss the observation and dynamics of such a monopole structure, and
note that the dynamics of the two-component monopole differs from the dynamics
of the three-component monopole.Comment: The focus of the paper is shifted towards creation and observation of
monopole
Electron Production in Proton Collisions: Total Cross Sections
Existing data on the ionization of neutral atoms and molecules by proton impact are reviewed, and electron production cross-section data are collected. The three major experimental methods are discussed and possible sources of error identified. Some theoretical cross sections are discussed, and well-established methods of relating them to measured cross sections are reviewed. A mathematical equation is fitted to the weighted experimental data for each target, and these fits are adjusted to be consistent with appropriate theoretical calculations and with electron impact and photoionization data. Recommended values of total cross sections for proton-impact ionization are given
Dissipative dynamics of vortex arrays in trapped Bose-condensed gases: neutron stars physics on K scale
We develop a theory of dissipative dynamics of large vortex arrays in trapped
Bose-condensed gases. We show that in a static trap the interaction of the
vortex array with thermal excitations leads to a non-exponential decay of the
vortex structure, and the characteristic lifetime depends on the initial
density of vortices. Drawing an analogy with physics of pulsar glitches, we
propose an experiment which employs the heating of the thermal cloud in the
course of the decay of the vortex array as a tool for a non-destructive study
of the vortex dynamics.Comment: 4 pages, revtex; revised versio
Natural & unnatural-parity contributions in electron-impact ionization of laser-aligned atoms
Differential cross section measurements from laser-aligned Mg atoms are compared to theoretical calculations using both time dependent and time-independent formalisms. It is found that both natural and unnatural parity contributions to the calculated cross sections are required to emulate the data when the state is aligned out of the scattering plane
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