A. Chetioui

Charge-state distributions of few-electron ions deduced from atomic cross sections

A model for the evolution of charge-state distributions of fast heavy ions in solid targets is formulated, applying to the case when highly stripped ions are produced. Starting from atomic cross sections, the authors calculate the evolution of the individual populations in 1s, 2s and 2p subshells resulting from a dynamical competition between atomic processes, like electron capture, ionisation, excitation, and radiative decay processes. The final charge-state fractions are calculated by combining these individual populations. Numerical calculations are compared with experimental data for 7 MeV u-1 Fe and 35 MeV u-1 Kr ions in various targets.

X-ray reflectivities, at low and high order of reflection, of flat highly oriented pyrolytic graphite crystals

Abstract Integrated reflectivities of flat highly oriented pyrolytic graphite crystals have been measured at various energies (5.9 ≤E ≤ 15.10 keV) and for various orders of reflection n (1 ≤n ≤ 5). For low n values, the reflectivity is severely affected by secondary extinction; our results show that the theory of Zachariasen represents the experiment reasonably well, a conclusion reached by other authors for the case of n = 1 reflections. For high n values, the reflectivity is more sensitive to the structure factors temperature correction, a quantity not precisely known. Our measurements are in favour of the larger temperature correction within the range reported in the literature.

New investigation of saturation effect in ion-atom excitation

Excitation cross sections of Kr34+ ions colliding with various target atoms, (Zt between 6 and 40) at nu =35 au have been investigated both experimentally and theoretically. The experimental cross sections were obtained from those for production of projectile He-like and H-like Lyman X-rays. The combined experimental and theoretical analysis of H-like emission allowed for a determination of the competitive capture-ionization process, whose contribution to the Lyman production cross sections is important for near-symmetric collision systems and has to be subtracted. A saturation effect of the experimental excitation cross sections with Zt is analysed from the theoretical point of view through atomic and molecular coupled-state calculations.

Characteristics of single capture nl distributions and double capture probabilities in slow collisions of Al13+, Al12+ and Ne9+ ions with two-electron targets (He, H2)

Relative intensities of Lyman X-rays consecutive to one- or two-electron capture have been measured for collisions of 4 keV u-1 Al13+, Al12+, Ne9+ ions with He and H2 targets. A method is presented to extract separate information on single and double transfer processes. Preferential n states, proportion of p substrates and mean l values populated by single capture are measured, together with double capture probabilities. Comparison of experimental results with theoretical predictions for one-electron systems with near-crossing radii suggest that the location of these crossings may be more important than target internal structure to determine final l distributions. Finally, for the investigated systems with different ionic charges but near-crossing radii, double capture probabilities are found to be quite similar.

Doubly excited states populated in collisions of O8+ ions with He and H2 at 1.24 keV amu-1

Coincidence measurements between O6+(3, 3), (3, 4) (or (4, 4)) ions and their emitted X-rays have been performed in double capture collisions between fully stripped O8+ ions and He (or H2) targets at 1.24 keV amu-1. Average ratios of autoionization widths towards different continuum states have been extracted for this measurement and compared with predictions of new Feshbach calculations. A complete set of theoretical partial autoionization widths for the singlet (3, 3), (3, 4) and (4, 4) states of O6+ is also given. In most cases the results exclude a dominant population of high-L states by double capture in contrast with previously reported measurements at higher velocities.

Excitation of Kr34+ ions at intermediate velocity

Abstract Total and partial excitation cross sections for 34 MeV/amu Kr34+ ions colliding with various targets (6 ≤ Zt ≤ 40) have been determined from projectile X-ray measurements. The results were compared to the predictions of a method based on Schwingers variational principle.

Alignment of Kr35+ np states in high velocity charge transfer collisions

Abstract Experimental alignments of some Kr35+ np states (n

Charge exchange collisions involving highly stripped ions: Distribution and anisotropy of final state angular momenta

= 4) populated by electron capture in 3 GeV Kr36+ ion-atom collisions are presented. A full comparison with theoretical CDW calculations is performed, which provides a further test of the applicability of this theory at the low side of the high energy range ( v p v i , v f ∼ 2 to 4 ).

Polarization factor measurements of flat crystals using synchrotron radiation

Abstract In this paper, physical effects responsible for l and m distributions in low energy capture process are discussed and a review of the physical content of various theories is given. Experimental data are reported for l, m capture cross sections for 4 keV u Ne9+ → H2 collisions and compared to theoretical predictions for the F9+ → H case.

Role of angular correlations and total angular momentum on partial autoionisation widths of O6+ (3,3) and (4,4) states

Abstract A method for measuring polarization factors of flat crystals, using a highly polarized beam source provided by synchrotron radiation, is presented. Application to the test of a graphite mosaic crystal, performed at the LURE-DCI facility in Orsay (France), is reported. Results concerning polarization factors at different energies are discussed in connection with measured crystal reflectivities.