L x‐ray fluorescence cross‐sections of heavy elements in the atomic region 57 ≤ Z ≤ 71 excited by 17.78 keV photons

L x‐ray fluorescence cross‐sections (σ_Lα, σ_Lβ, and σ_Lγ) were measured with an accuracy of 6% (except for the Lγ x‐ray line around 8%) for La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb and Lu at an excitation energy of 17.78 keV. Relative intensities I_Kβ/I_Kα and I_Lγ/I_Lα were also measured for the same elements. The measured cross‐sections were compared with experimental and theoretical values. Measurements of the emitted x‐rays were performed using an Si(Li) detector. Copyright © 2004 John Wiley & Sons, Ltd.     

Charge redistribution and a shortening of the Fe—As bond at the quantum critical point of SmO1–xFxFeAs

Many researchers have pointed out that there is a quantum critical point (QCP) in the F‐doped SmOFeAs system. In this paper, the electronic structure and local structure of the superconductive FeAs layer in SmO_1–xF_xFeAs as a function of the F‐doping concentration have been investigated using Fe and As K‐edge X‐ray absorption spectroscopy. Experiments performed on the X‐ray absorption near‐edge structure showed that in the vicinity of the QCP the intensity of the pre‐edge feature at the Fe‐edge decreases continuously, while there is a striking rise of the shoulder‐peak at the As edge, suggesting the occurrence of charge redistribution near the QCP. Further analysis on the As K‐edge extended X‐ray absorption fine structure demonstrated that the charge redistribution originates mostly from a shortening of the Fe—As bond at the QCP. An evident relationship between the mysterious QCP and the fundamental Fe—As bond was established, providing new insights on the interplay between QCP, charge dynamics and the local structural Fe—As bond in Fe‐based superconductors.     

The density and tube energy dependency of cobalt Kα/Kβ in x‐ray fluorescence spectrometryfor thick target measurements

The relative intensity of K_α/K_β for cobalt in thick targets with cobalt mass densities from 0.51 to 22.49% has been measured by the wavelength dispersive x‐ray fluorescence (XRF) spectrometer. The measuring conditions are: tube current ranging from 10 to 60 mA and voltages ranging from 20 to 60 kV. We plotted the K_α/K_β ratio vs Co densities for different tube voltages and currents. Our study shows that the K_α/K_β ratio is below the theoretical value for low Co densities and it increases with increasing Co density. For higher x‐ray energies, the K_α/K_β ratio shows a sharp growth at the special density and then reaches a nearly constant value. However, K_α/K_β ratio is theoretically constant and independent of energy in thin target measurements. The changes of this ratio according to the x‐ray energy and the element density have been studied in thick target measurements. The results provide experimental evidence to suggest that exciting energy and element density can indeed affect the K_α/K_β ratio. Copyright © 2008 John Wiley & Sons, Ltd.     

A study of KαL1 X‐ray satellite spectrum of the elements 27 ≤ Z ≤ 31 by photon excitation

K _α X‐ray satellite spectra of Co, Ni, Cu, Zn, and Ga generated by photon excitation are analyzed using a wavelength dispersion spectrometer. Spectra of Ni, Cu, Zn, and Ga are studied for the first time using a LiF420 crystal. Spectrum of Co was studied with LiF200 crystal in second order. K_αL¹ X‐ray satellite energies and relative intensities are measured. The energy shifts relative to diagram line are computed and are compared with theoretical and semi‐empirical values. Dependence of energy shifts and relative intensities on Z and mode of excitation is analyzed.     

Measurements of L subshell and L shell x‐ray fluorescence cross‐sections for U and Th

The Ll, Lα_{1, 2}, Lη, Lβ₆, Lβ_{2, 4, 15, 17}, Lβ_{1, 3, 5}, Lβ_{9, 10}, Lγ₁, Lγ_{2, 3, 6, 8}, Lγ_4,4′ and Lγ₅ x‐ray fluorescence cross‐sections for U and Th were measured at 59.5 keV incident photon energy by using theoretical L_i subshell photoelectric cross‐sections, fluorescence and Coster–Kronig yields and fractional emission rates, and calculated theoretically by using atomic parameters. The measured values were compared with the theoretical values and experimental results available in the literature. Copyright © 2003 John Wiley & Sons, Ltd.     

Residual‐density mapping and site‐selective determination of anomalous scattering factors to examine the origin of the Fe K pre‐edge peak of magnetite

The electron‐density distribution and the contribution to anomalous scattering factors for Fe ions in magnetite have been analyzed by X‐ray resonant scattering at the pre‐edge of Fe K absorption. Synchrotron X‐ray experiments were carried out using a conventional four‐circle diffractometer in the right‐handed circular polarization. Difference‐Fourier synthesis was applied with a difference in structure factors measured on and off the pre‐edge (E_on = 7.1082 keV, E_off = 7.1051 keV). Electron‐density peaks due to X‐ray resonant scattering were clearly observed for both A and B sites. The real part of the anomalous scattering factor f′ has been determined site‐independently, based on the crystal‐structure refinements, to minimize the squared residuals at the Fe K pre‐edge. The f′ values obtained at E_on and E_off are ?7.063 and ?6.682 for the A site and ?6.971 and ?6.709 for the B site, which are significantly smaller than the values of ?6.206 and ?5.844, respectively, estimated from the Kramers–Kronig transform. The f′ values at E_on are reasonably smaller than those at E_off. Our results using a symmetry‐based consideration suggest that the origin of the pre‐edge peak is Fe ions occupying both A and B sites, where p–d mixing is needed with hybridized electrons of Fe in both sites overlapping the neighbouring O atoms.     

Strikingly dissimilar effect of Mn and Zn dopants imposed on local structural distortion of Ba0.5K0.5Fe2As2 superconductor

To clarify the contrasting impurity effects of Mn and Zn dopants on the critical temperature of optimally doped Ba_0.5K_0.5Fe₂As₂ superconductors, extended X‐ray absorption fine‐structure spectroscopy was implemented at the Fe and As K‐edge. In Mn‐doped compounds a gradual deviation of the symmetric FeAs₄ tetrahedron and weakening of the Fe—As bond was observed. Conversely, in Zn‐doped compounds the perfect FeAs₄ tetrahedron is maintained and the Fe—As bond is rigid. The local structural details are consistent with the development of superconductivity in these two systems, suggesting a significant role played by the topology of the FeAs₄ tetrahedron and rigidness of the Fe—As bond in Mn/Zn‐doped Ba_0.5K_0.5Fe₂As₂ superconductors.     

Quantitative analysis of Mo–Si–B alloy phases with wavelength dispersive spectroscopy (WDS–SEM)

Mo–Si–B alloys show great potential as high temperature materials. Due to peak overlapping of B‐K_α and Mo‐M_ζ, analyzing these alloys with microanalysis presents a real challenge. This paper describes the analytical methodology used to qualify and quantify the boron content in these alloys without stoichiometric reference samples by the use of a single parallel‐beam wavelength dispersive spectrometer. Characterization of boron is performed by using a coupled energy dispersive X‐ray spectroscopy—wavelength dispersive spectroscopy system in a scanning electron microscope. Self‐made pure element samples are used for calibration and quantification of the boron content.     

Study of absorption parameters around the K edge for selected compounds of Gd

The K shell absorption jump ratios, jump factors, effective atomic numbers, and electron densities were derived from the measured total mass attenuation coefficient using an energy dispersive X‐ray fluorescence spectrometer for Gd₂O₃, Gd₂(CO₃)₃H₂O, Gd₂(C₂O₄)₃H₂O, and Gd₂(SO₄)₃ compounds. The total mass attenuation coefficients were measured in the X‐ray energy range from 39.52 to 57.14 keV in a transmission geometry utilizing the Kα₂, Kα₁, Kβ₁, and Kβ₂ X‐rays from different secondary source targets excited by the 59.54‐keV photons from an Am‐241 annular source and detected by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. The energy gap, ionization energy, electron affinity, and global electrophilicity parameters of oxide, sulfate, oxalate, and carbonate ions were calculated using density functional theory (B3LYP). The experimental results are discussed based on these parameters. Copyright © 2015 John Wiley & Sons, Ltd.     

Three dimensional (Z‐dependence), collective and individual semi‐empirical formulae for L X‐ray production and ionization cross section by protons impact within corrected ECPSSR theory and updated experimental data: a review

In this paper we propose a new three dimensional semi‐empirical formulae for the deduction of L X‐ray production and ionization cross sections by introducing the dependence on the atomic number of the target, noted as ‘Z‐dependence’. The data are also fitted collectively and separately (for each element) by analytical functions to calculate semi‐empirical cross sections. For this purpose, the corrected ECPSSR model (noted as eCPSSR) and the published experimental data of L_α, L_β and L_γ X‐ray production and L₁, L₂ and L₃ ionization cross sections in the period (1950–2014) are combined to calculate the semi‐empirical ones for a wide range of elements by proton impact. The semi‐empirical cross sections (for the three x‐rays lines L_α, L_β, L_γ and the three sub‐shells L₁, L₂, L₃) are then deduced by fitting the available experimental data normalized to their corresponding theoretical values (using the eCPSSR model) giving a better representation of the experimental data for the individual interpolation. At last, a comparison is made between the three semi‐empirical formulae reported in this work. Copyright © 2016 John Wiley & Sons, Ltd.