Jean-Claude Dousse

The high‐resolution spectra of thorium Mα _{1 , 2} ( M ₅ → N _{6 , 7} ) and Mβ ₁ ( M ₄ → N ₆ ) x‐ray lines induced by an impact of O ions with energy 376.0 MeV were measured using a von Hamos crystal spectrometer in order to study the x‐ray emission from multiple ionized atoms. The observed x‐rays have been interpreted in terms of the relativistic multiconfiguration Dirac‐Fock (MCDF) calculations performed for dominating vacancy configurations expected to contribute to the measured spectra. Due to the complexity of such calculations for selected multi‐vacancy configurations the simplified average < MCDF > model, combining the MCDF calculations and binomial distribution of vacancies has been used. The measured spectra clearly exhibit a rich structure of Mα _{1 , 2} x‐ray satellites of thorium, including the transitions from the multivacancy initial configurations M ⁻¹ N ^{− n} as well as the hypersatellites corresponding to the transitions in complex multivacancy initial configurations M ^{− m} N ^{− n} ( m,n ≤ 4). The present interpretation of the measured satellite/hypersatellite structure of Mα _{1 , 2} ( M ₅ → N _{6 , 7} ) x‐ray transitions allows us to determine the ionization probabilities for the M ‐ and N ‐shell in central collisions. The measured ionization probabilities are compared with the theoretical predictions of the geometrical model (GM), and the semiclassical approximation (SCA) using both the Dirac hydrogenic and Dirac‐Hartree‐Fock selfconsistent wave functions.

We report on novel reference-free methods to determine the instrumental resolution of transmission-type bent crystal spectrometers. The novel methods are based on the measurements of a selected X-ray line in several orders of diffraction. It is shown that the angular broadening of the spectrometer and the natural linewidth of the selected transition can be obtained directly from the novel methods. No reference X-ray line or γ-ray line is needed. The precision of the results is about 10 times better than the one obtained with the standard method consisting of measuring a reference X-ray line and keeping fixed in the fit the natural width of this line at the value taken from available databases. The novel methods are illustrated for a DuMond-type bent crystal spectrometer with the Kα₁ X-ray line of Gd measured in the first five orders of diffraction.

We report on a laboratory-based facility for in-house x-ray absorption fine structure (XAFS) measurements. The device consists of a conventional x-ray source for the production of the incident polychromatic radiation and a von Hamos bent crystal spectrometer for the analysis of the incoming and transmitted radiation. The reliability of the laboratory-based setup was evaluated by comparing the Cu K-edge and Ta L3-edge XAFS spectra obtained in-house with the corresponding spectra measured at a synchrotron radiation facility. To check the accuracy of the device, the K- and L-edge energies and the attenuation coefficients below and above the edges of several 3d, 4d, and 5d elements were determined and compared with the existing experimental and theoretical data. The dependence of the XAFS spectrum shape on the oxidation state of the sample was also probed by measuring inhouse the absorption spectra of metallic Fe and two Fe oxides (Fe2O3 and Fe3O4).

We report on high energy resolution measurements of the Kα hypersatellite x-ray spectra of Ca, V, Fe and Cu induced by impact with 144 MeV C and 180 MeV Ne ions.

Single-photon double K-shell ionization of low-Z neutral atoms in the range 12$\leqslant${}Z$\leqslant${}23 is investigated. The experimental method was based on measurements of the high-resolution K$\alpha${}h hypersatellite x-ray spectra following the radiative decay of the K-shell double-vacancy states excited by monochromatic synchrotron radiation. The photon energy dependence of the double K-shell ionization was measured over a wide range of photon energies from threshold up to and beyond the maximum of the double-to-single photoionization cross section ratios. From the high-resolution x-ray emission spectra the energies and linewidths of the hypersatellite transitions, as well as the K$\alpha${}1h:K$\alpha${}2h intensity ratios, were determined. The relative importance of the initial-state and final-state electron-electron interactions to the K-shell double photoionization is addressed. Physical mechanisms and scaling laws of the K-shell double photoionization are examined. A semiempirical universal scaling of the double-photoionization cross sections with the effective nuclear charge for neutral atoms in the range 2$\leqslant${}Z$\leqslant${}47 is established.