M. Berset

Relative detection efficiency of back- and front-illuminated charge-coupled device cameras for x-rays between 1 keV and 18 keV

High-resolution x-ray measurements were performed with a von Hamos-type bent crystal spectrometer using for the detection of the diffracted photons either a back-illuminated charge-coupled device (CCD) camera or a front-illuminated one. For each CCD the main x-ray emission lines (e.g., Kalpha, Kbeta, Lalpha, and Lbeta) of a variety of elements were measured in order to probe the performances of the two detectors between 1 and 18 keV. From the observed x-ray lines the linearity of the energy response, the noise level, the energy resolution, and the quantum efficiency ratio of the two CCDs were determined.

Observation of L-X-ray satellites and hypersatellites in collisions of O and Ne ions with Mo and Pd

Abstract The satellite structure of Lα 1,2 and Lβ 1 X-ray transitions in 42 Mo and 46 Pd induced by an impact of O and Ne ions with energies 178–376 MeV have been studied with a high-resolution von Hamos crystal spectrometer. The observed M-shell satellites of the diagram Lα 1,2 and Lβ 1 lines are affected mostly by one- and two-vacancy configurations for oxygen ions and much more complex multi-vacancy configurations for neon impact. The L-shell hypersatellites are clearly observed in the measured spectra, both for Lα 1,2 and Lβ 1 X-ray transitions. The spectra are compared with the predictions of the multi-configuration Dirac–Fock (MCDF) calculations performed for up to two additional vacancies. Such MCDF calculations reproduce the main features of the M-shell satellite structure observed for oxygen ions, but they fail to describe the X-ray spectra measured for neon ions. Clearly, more complex multi-vacancy configurations have to be included in the MCDF calculations to achieve quantitative agreement in this case. The measured X-ray satellite structure for neon ions is thus interpreted by means of a simplified binomial model based on the average MCDF X-ray shifts and independent electron picture of multiple ionization of atoms by ion impact.

High-resolution Laue-type DuMond curved crystal spectrometer

We report on a high-resolution transmission-type curved crystal spectrometer based on the modified DuMond slit geometry. The spectrometer was developed at the University of Fribourg for the study of photoinduced X-ray spectra. K and L X-ray transitions with energies above about 10 keV can be measured with an instrumental resolution comparable to their natural linewidths. Construction details and operational characteristics of the spectrometer are presented. The variation of the energy resolution as a function of the focal distance and diffraction order is discussed. The high sensitivity of the spectrometer is demonstrated via the 2s-1s dipole-forbidden X-ray transition of Gd which could be observed despite its extremely low intensity. The precision of the instrument is illustrated by comparing the sum of the energies of the Au K-L2 and L2-M3 cascading transitions with the energy of the crossover K-M3 transition as well as by considering the energy differences of the Gd Kα1 X-ray line measured at five different diffraction orders. Finally, to demonstrate the versatility of the spectrometer, it is shown that the latter can also be used for in-house extended X-ray absorption fine structure measurements.

High-resolution study of the x-ray resonant Raman scattering process around the 1s absorption edge for aluminium, silicon, and their oxides

X-ray resonant Raman scattering (RRS) spectra of Al, Al{sub 2}O{sub 3}, Si, and SiO{sub 2} were measured at the European Synchrotron Radiation Facility, using a high-resolution Bragg-type curved crystal spectrometer. The x-ray RRS spectra were collected at several beam energies tuned below the 1s absorption thresholds of Al and Si. Differences in the spectral features between the elemental samples and the oxide ones were clearly observed. The data were interpreted using the second-order perturbation theory within the Kramers-Heisenberg (KH) approach. It is shown that, using the KH formalism, oscillator strengths that are similar to the ones deduced from x-ray absorption measurements can be extracted from emission x-ray RRS spectra. The total cross sections for the x-ray RRS process were derived for the different photon beam energies and compared with theoretical predictions. For elemental silicon, the weak 1s-3p excitation was observed and found to be consistent with results of density of states calculations.

Observation of internal structure of the L-shell x-ray hypersatellites for palladium atoms multiply ionized by fast oxygen ions

An observation of the internal structure of the L-shell hypersatellite x rays resulting from the one-photon decay of L{sup -2} double-vacancy states in palladium multiply ionized by oxygen ions is reported. The Pd L{sub 3}{yields}M{sub 4,5} x-ray spectrum was measured with a von Hamos high-resolution crystal spectrometer. The complex shape of the observed spectrum could be interpreted in detail using relativistic multiconfiguration Dirac-Fock calculations. The relative intensities of the measured x rays were found to be in good agreement with semiclassical approximation calculations using relativistic Dirac-Hartree-Fock wave functions.

Vacancy rearrangement processes in multiply ionized atoms

We demonstrate that in order to interpret the x-ray satellite structure of Pd Lα1,2(L3M4,5) transitions excited by fast O ions, which was measured using a high-resolution von Hamos crystal spectrometer, the vacancy rearrangement processes, taking place prior to the x-ray emission, have to be taken into account. The measured spectra were compared with the predictions of the multi-con.guration Dirac-Fock (MCDF) calculations using the fluorescence and Coster-Kronig yields which were modiffed due to a reduced number of electrons available for relaxation processes and the effect of closing the Coster-Kronig transitions. We demonstrate that the vacancy rearrangement processes can be described in terms of the rearrangement factor, which can be calculated by solving the system of rate equations modelling the flow of vacancies in the multiply ionized atom. By using this factor, the ionization probability at the moment of collision can be extracted from the measured intensity distribution of x-ray satellites. The present results support the independent electron picture of multiple ionization and indicate the importance of use of Dirac-Hartree-Fock wave functions to calculate the ionization probabilities.

M-subshell ionization in near-central collisions of 20-MeV/amu carbon ions with molybdenum atoms

Abstract The Kβ spectrum of 42 Mo bombarded by 20.8 MeV/amu carbon ions was measured with high-resolution using a transmission-type bent crystal spectrometer operated in the modified DuMond slit geometry. The M-shell satellites of the Kβ 2 transition could be well resolved, whereas for the Kβ 1,3 transitions only a broadening and shift of the line centroid was observed. The composite structure of the satellite lines which consist of many components that vary in energy and strength was analyzed using theoretical energies and relative intensities obtained from multiconfiguration Dirac–Fock calculations. From the data analysis average M-shell satellite-to-diagram line yield ratios were deduced for both the Kβ 1,3 and Kβ 2 transitions. For the Kβ 2 transition for which the relative contributions of the 3s,p and 3d spectator vacancies to the observed Kβ 2 M 1 satellite yield could be determined, separated X(Kβ 2 M 1 1,2,3 ):X(Kβ 2 M 0 ) and X(Kβ 2 M 1 4,5 ):X(Kβ 2 M 0 ) yield ratios could even be extracted.

High energy resolution measurements of the radiative decay of double K-shell vacancies in 20 ≤ Z ≤ 29 elements bombarded by fast C and Ne ions

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.

High-resolution KMM radiative Auger x-ray emission spectra of calcium induced by synchrotron radiation

The KMM radiative Auger (RA) x-ray spectra of solid Ca were induced by monochromatic synchrotron radiation and measured with a high-resolution von Hamos bent crystal spectrometer. Two excitation energies were employed, one in the near K threshold region and the second well above the K absorption edge. The KMM RA spectral structure and relative intensity with respect to the diagram K{beta}{sub 1,3} (K-M{sub 3,2}) line are found to be independent of the excitation energy. The overall RA structure resembles the density of unoccupied s, p, and d states. Due to solid-state effects, however, spectral features resulting from the major discrete shake-up transitions could not be resolved. For the total KMM RA to K{beta}{sub 1,3} yield ratio, a value of 0.053(3) is obtained. The latter is compared to theoretical predictions and available experimental data obtained by various types of target excitation.

Double K-shell photoionization and universal scaling laws

The photon energy dependence of the double K-shell ionization cross sections for light atoms and He-like ions is reported. The K-shell double photoionization DPI cross-sections for hollow atom production are compared to those of the corresponding He-like counterparts. The relative contribution of the initial-state correlations and final-state electron-electron interactions to the K-shell DPI is addressed. A semiempirical universal scaling of the double photoionization cross sections with the effective nuclear charge for neutral atoms in the range 2 ≤ Z ≤ 47 is established.