arXiv subjects

Igor Bray

Publications and source records attributed to Igor Bray.

23 records · Page 2Linked to original sources

arXiv1999

Electron-impact ionization of atomic hydrogen from near threshold to high energies

Application of the convergent close-coupling (CCC) method to electron-impact ionization of the ground state of atomic hydrogen is considered at incident energies of 15.6, 17.6, 20, 25, 27.2, 30, 54.4, 150 and 250 eV. Total through to fully differential cross sections are presented. Following the analysis of Stelbovics [submitted to Phys. Rev. Lett. (physics/9905020)] the equal-energy sharing cross sections are calculated using a solely coherent combination of total-spin-dependent ionization amplitudes, which are found to be simply a factor of two greater than the incoherent combination suggested by Bray and Fursa [1996 Phys. Rev. A {\bf 54}, 2991]. As a consequence, the CCC theory is particularly suited to the equal-energy-sharing kinematical region, and is able to obtain convergent absolute scattering amplitudes, fully ab initio. This is consistent with the step-function hypothesis of Bray [1997 Phys. Rev. Lett. {\bf 78}, 4721], and indicates that at equal-energy-sharing the CCC amplitudes converge to half the step size. Comparison with experiment is satisfactory in some cases and substantial discrepancies are identified in others. The discrepancies are generally unpredictable and some internal inconsistencies in the experimental data are identified. Accordingly, new (e,2e) measurements are requested.

physics.atom-ph↗

arXiv1999

A study of cross sections for excitation of pseudostates

Using the electron-hydrogen scattering Temkin-Poet model we investigate the behavior of the cross sections for excitation of all of the states used in the convergent close-coupling (CCC) formalism. In the triplet channel, it is found that the cross section for exciting the positive-energy states is approximately zero near-threshold and remains so until a further energy, equal to the energy of the state, is added to the system. This is consistent with the step-function hypothesis [Bray, Phys. Rev. Lett. {\bf 78} 4721 (1997)] and inconsistent with the expectations of Bencze and Chandler [Phys. Rev. A {\bf 59} 3129 (1999)]. Furthermore, we compare the results of the CCC-calculated triplet and singlet single differential cross sections with the recent benchmark results of Baertschy et al. [Phys. Rev. A (to be published)], and find consistent agreement.

physics.atom-ph↗

arXiv1999

Electron-impact ionization of atomic hydrogen at 2 eV above threshold

The convergent close-coupling method is applied to the calculation of fully differential cross sections for ionization of atomic hydrogen by 15.6 eV electrons. We find that even at this low energy the method is able to yield predictive results with small uncertainty. As a consequence we suspect that the experimental normalization at this energy is approximately a factor of two too high.

physics.atom-ph↗

arXiv1998

Quantum-mechanical calculation of Stark widths of Ne VII n=3, $Δn=0$ transitions

The Stark widths of the Ne VII 2s3s-2s3p singlet and triplet lines are calculated in the impact approximation using quantum-mechanical Convergent Close-Coupling and Coulomb-Born-Exchange approximations. It is shown that the contribution from inelastic collisions to the line widths exceeds the elastic width contribution by about an order of magnitude. Comparison with the line widths measured in a hot dense plasma of a gas-liner pinch indicates a significant difference which may be naturally explained by non-thermal Doppler effects from persistent implosion velocities or turbulence developed during the pinch implosion. Contributions to the line width from different partial waves and types of interactions are discussed as well.

physics.atom-ph↗

arXiv1997

Stark Broadening of the B III 2s-2p Lines

We present a quantum-mechanical calculation of Stark line widths from electron-ion collisions for the $2s_{1/2}-2p_{1/2,3/2}$, lambda = 2066 and 2067 A, resonance transitions in B III. The results confirm the previous quantum-mechanical R-matrix calculations but contradict recent measurements and semi-classical and some semi-empirical calculations. The differences between the calculations can be attributed to the dominance of small L partial waves in the electron-atom scattering, while the large Stark widths inferred from the measurements would be substantially reduced if allowance is made for hydrodynamic turbulence from high Reynolds number flows and the associated Doppler broadening.

physics.atom-ph↗