Crystal Diffraction Spectrometer Research Articles

Assessment of the possibility of X-ray fluorescence analysis before conducting the experimental work

The article proposes an approach to the development of a method for X-ray fluorescence analysis of an object using crystal-diffraction spectrometers prior to the experimental work. In case when the X-ray fluorescence analysis method is intended as a substitute for an existing method, then for the object being analyzed the statistical characteristics of the material for which the X-ray fluorescence analysis method is being developed, i.e. the average content of the elements to be determined, the dispersion and the range of the elements content, the requirements for the accuracy of determination, and some others, are calculated on the basis of archival data of the analytical laboratory (or an array of selected calibration samples). In case when a new method is developed, technical requirements for the product allowing estimating these characteristics are sufficient. Analytical characteristics, such as basic instrumental error, sensitivity, spectral resolution, contrast, must be measured and calculated over the entire operating range of the measured analytical lines for the spectrometer used. Metrological characteristics of the method for determining the elements, i.e. detection limit, differential sensitivity, instrumental reproducibility of content measurement at the selected exposure time, are evaluated on the basis of these data. At this stage the question concerning the necessity of diluting the samples with a heavy or light diluent for obtaining satisfactory differential sensitivity may be resolved. The regimes for recording the analytical signal for the elements to be analyzed, i.e. analytical lines, analyzer crystals, X-ray tube operating modes, are determined, the probability of overlapping spectral lines is estimated, and the background measurement points are selected. Calculation of theoretical and simulation of experimental intensities for selected calibration and test samples and calculation of theoretical coefficients of influence are carried out. The expected error of the analysis is estimated on the basis of the statistical characteristics of the material and the theoretical coefficients of influence, and the need to take into account the relationship between the interfering elements in the equations is determined for achieving the required accuracy of determining the elements. Selection of regression or theoretical coupling equations, which provide the required accuracy of determining the elements, is carried out on the basis of the simulated experimental intensities of the analytical lines of the elements. Such approach allows a priory estimate the possibility of developing an X-ray fluorescence analysis technique for an object selected, and can significantly reduce time for performing the experimental work. Keywords: X-ray fluorescence analysis, method of analysis, analyzed object, X-ray spectrometer, analysis characteristics, forecast of experimental intensities, estimation of expected error, modes of registration of the analytical signal, coupling equations.

Express X-ray fluorescent analysis of technical-grade tantalum and niobium: from raw materials to products

Determination of impurities in Ta- and Nb-based materials is a necessary operation in supporting technological processes. The existing approaches involve the transfer of a sample into a solution with subsequent isolation of impurities. This procedure is rather complicated and takes a lot of time. For this reason, it is of interest to study the possibilities of direct analysis of solid-phase samples of materials, e.g., X-ray fluorescence analysis (XRF). The usual scheme of X-ray fluorescence analysis, which involves the experimental construction of calibration characteristics for each element to be determined, requires using a large number of reference samples containing a rather wide range of impurities. We present the results of preliminary characterization of samples of technical-grade tantalum and niobium and products on their base. It is shown that for starting materials, only a significant absence of impurities can be determined using XPA, but even for sintered niobium hydride and Ta powder, XPA can be used as a method for rapid assessment of the composition. A SPECTROSCAN MAX GVM crystal-diffraction spectrometer can be used for analysis and a standard software that implements the fundamental parameter method (FPA) can be used for calibration. In this case, the obtained values of the content of impurities may differ by 1 – 2 orders of magnitude from the reference values. However, such an accuracy is often enough to correct technological processes. The limits of detecting impurities by XRF in Ta- and Nb-based materials are revealed: for elements determined by K-series (from Ti to Co), the detection limits lie in the range from 30 to 60 ppm, whereas for the elements determined by M-series (Ta) the detection limit is approximately 200 ppm and for L-series (Nb) the detection limit is in the range from 100 to 150 ppm.

Hydrogen bonds promoted formation of Eu(III)-based host-guest complex and luminescence properties

Host-guest interaction is widely employed as a powerful tool to create supramolecular assembles with multicomponent units. In this work, an emissive quinoline-based tripodal acceptor L1 with tunable syn and anti-conformers was synthesized and used as host. Upon binding with guest species, Eu(III)-based host–guest complex 1 (L1 ⊃ [Eu(NO3)3(H2O)(CH3OH)2]) was constructed via host–guest interaction driven by multiple hydrogen bonds. Furthermore, in this complex, host conformation motion and Eu(III)–centered emission enhancement behavior are also observed by X-ray single crystal diffraction and fluorescence spectrometer. Theoretically, Density Functional Theory (DFT) calculations revealed that the anti and syn-conformations are stabilized by complexation of solvated lanthanide ions within cavity of tripodal host L1, respectively. The calculations were in good agreement with the experimental data. Moreover, emissive host–guest complex 1 could be used as an imaging regent in living cell potentially.

New rotational levels in 186Re nucleus

Excited levels of 186Re have been studied using results of the single γ-ray spectra measurements following the thermal neutron capture reaction. Energies and intensities of more than 500 γ-transitions have been obtained with the high-resolution crystal diffraction spectrometer GAMS5 of ILL. Most of the obtained intense γ-transitions have been placed in the 186Re level scheme. A number of new levels, as well as the depopulation for levels observed earlier in the 187Re(p,d)186Re reaction measurements have been proposed. Structure of 186Re levels is interpreted in terms of two-quasiparticle plus rotor coupling model and compared with that of the neighbouring doubly-odd nucleus 188Re.

Levels of 188Re nucleus populated in thermal neutron capture reaction

Levels of 188Re populated in thermal neutron capture reaction with enriched 187Re targets have been studied. Single γ-ray spectrum of 188Re, measured with the high-resolution crystal diffraction spectrometer GAMS5, as well as γγ-coincidence experiments performed with high efficiency Ge detectors, allowed to develop model-independent level scheme of the doubly-odd 188Re nucleus up to ∼1.5 MeV excitation energy. Analysis of the established 188Re level scheme in terms of the quasiparticle-plus-rotor model indicates coexistence of axially-deformed and triaxial structures in the energy range above 400 keV.

X-ray spectroscopy of multicharged xenon ions at the EBIT plasma

SynopsisX-ray spectra of multicharged xenon ions created in an electron-beam ion trap (EBIT) were measured both with a low-resolution silicon drift detector (SDD) and a high-resolution Johann/Johannson type crystal diffraction spectrometer. The measurement were performed in the electron-beam ion source (EBIS) using the transmission, leaky and pulsed modes of the ion source operation with trapped xenon ions excited by an electron beams of energies 9-15 keV. Moreover, the dynamics and equilibration of the EBIT plasma was studied by measuring the X-ray spectra for different electron energies and trapping times. The results will be discussed using available theoretical models describing the atomic processes in the EBIT plasma.

Estimation of microblock sizes in mosaic crystals according to fast electron radiation characteristics

The possibilities of a previously proposed technique for determining the characteristic sizes of microblocks in mosaic aα-class crystals have been analyzed. Determination is performed according to the ratio between the measured and calculated values for the diffraction suppression of the fixed-energy bremsstrahlung yield. The limits of applicability of the technique have been revealed. It is demonstrated that the technique can be implemented in an electron accelerator with the average energy Ee ∼ 30–40 MeV and long baselines making it possible to use crystal-diffraction spectrometers. The influence of microblock sizes on coherent electromagnetic processes in real crystals is discussed.

Influence of crystal mosaicity on the X-radiation characteristics observed at a small angle to the particle velocity direction

The experimentally measured yields of X-rays generated by 500-MeV electrons (the X-ray energies are ω ∼ γωp) in oriented tungsten single crystals are analyzed. A series of experiments have been performed at the Tomsk synchrotron with the use of crystal-diffraction spectrometers based on mosaic pyrolytic graphite crystals. The measured results are shown to be explained by competition between parametric X-radiation and bremsstrahlung diffraction in mosaic crystals of the aα class. The characteristic sizes of microblocks of refractory metal crystals are discussed from the standpoint of their influence on the positron yield in designed positron sources. A method for determining the characteristic sizes of microblocks in mosaic crystals of the aα class is proposed.

Study of the electron structure of Mn, Sr, La, Ce, and Sm cations in Ln1 − x Sr x MnO3 (Ln = La, Ce, Sm) manganites by the X-ray line shift method

The X-RayKα line shifts of all cations in Ln1 − xSrxMnO3 (Ln = La, Ce, Sm) manganites have been measured using crystal diffraction spectrometers. The Mn Kαline shifts have been found in the Sm1 − xSrxMnO3 system correspond to an increase in the valence from Mn3+ to Mn4+. In the Ce1 − xSrxMnO3 system, in addition to this, the valence of cerium have been found also increases to almost 4. It is shown that the dependence of the valence of manganese on the content of strontium does not correspond to a simple model of the local mixture of Mn3+ and Mn4+ ions, which is usually applied to these systems. It is also demonstrated that the bonds of Sr, La, and Sm in the manganites studied exhibit a significant covalent character. In cation-deficient Sm1 − yMn1 − zO3, an increase in the valence of Mn is found accompanied by a decrease in the covalence of Sm.

Johann crystal diffraction spectrometer for measuring small chemical shifts of soft X-ray lines

A new crystal diffraction spectrometer constructed at the St. Petersburg Nuclear Physics Institute (NPI) according to the Johann scheme is described. The instrument is intended for studying the electron structure of light elements, in particular, 3d metals (beginning with scandium) in their compounds. The working energy range is 4–15 keV. A specific feature of this Johann spectrometer is that this instrument (like the Cauchois spectrometers also available at the PNPI) is capable of simultaneously measuring chemical shifts and the other parameters of X-ray lines of the same element in two compounds possessing specific physical properties (valence, magnetoresistance, etc.). With the proposed spectrometer, it is possible to study the electron structure of elements from Sc to Br using lines of the K series and from Ba to Pb using lines of the L series. Extensive investigations in this field of solid-state physics are important in both experimental and theoretical aspects.

Effect of the chemical state of uranium atom on the energy of spin-orbital splitting of its inner orbitals

Summary Chemical shifts (ChSh) of nine emission lines of the uranium L-series in uranium oxides UO2+ x (x=0-1) with respect to UO2 were studied by using a precise crystal-diffraction X-ray spectrometer. ChSh of Lα 1,α 2 uranium and thorium lines in solid solutions yUO2·(1-y )ThO2 (y=0:1) were measured with respect to UO2 and ThO2, respectively. The changes in energy of spin-orbital splitting (SOS) — Δδnl ± of inner nl-orbitals of the uranium atom were calculated from the data of ChSh of spin-doublet lines. For UO2+ x oxides, a linear decrease in Δδnl ± values with increasing degree of uranium oxidation was found. Sign inversion of Δδnl ± for uranium levels was found on passing to solid solutions. No change in the SOS energy of inner thorium levels was detected. The values of Δδnl ± were found to correlate with the experimental values of the effective magnetic moment of uranium in oxides. On the basis of the comparison of experimental Δδnl ± values with Dirac–Hartree–Fock atomic calculations, it was concluded that the observed variations in Δδnl ± values are due to the redistribution of electron and spin density between the 5f 7/2- and 5f 5/2-levels of the fine structure of the uranium atom without changes in atomic charge state. On the basis of the hypothesis of intraatomic relativistic U5f 7/2↔U5f 5/2 transition, a model of paramagnetic moment formation on the uranium atom in uranium dioxide was proposed.

Role of Spin-Orbital Splitting of 5f-Orbitals of Uranium Atom in the Formation of Its Chemical State

ABSTRACTChemical shifts (ChSh) of nine emission lines of the uranium L-series in uranium oxides UO2+x (x=0−1) with respect to UO2 were studied by using a precise crystal-diffraction X-ray spectrometer and the changes in energy of spin-orbital splitting (SOS) − Δδnl± of inner nl-orbitals of the uranium atom were calculated from the data of ChSh of spin-doublet lines. For UO2+x oxides, a linear decrease in Δδnl± values with increasing degree of uranium oxidation was found.On the basis of the comparison of experimental Δδnl± values with Dirac-Hartree-Fock atomic calculations, it was concluded that the observed variations in Δδnl± values are due to the redistribution of electron and spin density between the 5f7/2- and 5f5/2-levels of the fine structure of the uranium atom without changes in atomic charge state.

Diffraction of real and virtual photons in a pyrolytic graphite crystal as source of intensive quasimonochromatic X-ray beam

A series of experiments on the parametric X-rays radiation (PXR) generation and radiation soft component diffraction of relativistic electrons in pyrolytic graphite (PG) crystals have been carried out at the Tomsk synchrotron. It is shown that the experimental results with PG crystals are explained by the kinematic PXR theory if we take into account a contribution of the real photons diffraction (transition radiation, bremsstrahlung and PXR photons as well). The measurements of the emission spectrum of channeled electrons in the photon energy range much smaller than the characteristic energy of channeling radiation have been performed with a crystal-diffraction spectrometer. For electrons incident along the 〈1 1 0〉 axis of a silicon crystal, the radiation intensity in the energy range 30⩽ ω⩽360 keV exceeds the bremsstrahlung one almost by an order of magnitude. Different possibilities to create an effective source of the monochromatic X-ray beam based on the real and virtual photons diffraction in the PG crystals have been considered.

X-ray Spectroscopy of Neon-like Xenon at the Dresden EBIT

X-ray spectroscopic measurements of highly charged xenon ions produced in the Dresden electron beam ion trap (DEBIT) are presented and compared to simulation results. The measurements are done using both a Si(Li) solid state detector and a crystal diffraction spectrometer being equipped with a SiO2 (101̄0) crystal and an energy sensitive CCD camera. The simulation is performed by a code that calculates the charge state evolution in an EBIT by solving the particle and energy rate equations. In addition the energies of the most intensive lines of the wavelength dispersive spectrum are compared to calculations using the GRASP atomic structure code. The calculated charge states and energies are in good agreement with the experimental results.

Soft Component of Emission from Channeled Electrons in a Silicon Crystal

The Tomsk synchrotron has been used to measure the emission spectrum and orientation dependences of the yield of photons with energies much smaller than the emission energy of channeled electrons. The measurements have been performed with a crystal-diffraction spectrometer. For electrons incident along the (110) axis, the radiation intensity in the energy range 30 ≤ ω ≤ 360 keV exceeds the bremsstrahlung one by almost an order of magnitude. The shape of the emission spectrum does not coincide with that of the bremsstrahlung spectrum. The radiation intensity increases smoothly with the photon energy. The bremsstrahlung spectrum from a disoriented crystalline target is satisfactorily described by the existing theory with phenomenological consideration of the polarization of the medium.

He-like hole states in mid- Z atoms studied by high-resolution K X-ray spectroscopy

High-resolution measurements of the Kα 1,2 X-ray spectra were performed with a bent crystal diffraction spectrometer for zirconium, niobium, molybdenum and palladium targets bombarded by 280 and 360 MeV oxygen ions. The energy differences between the Kα 1,2 diagram and the K h α 1,2 hypersatellite transitions as well as the intensity ratios I( K h α 1)/ I( K h α 2) were determined. The L-shell satellites of the diagram and of the hypersatellite lines were resolved. The data are interpreted in terms of the properties of He-like hole states in mid- Z atoms. The Breit interaction correction is determined. The corrections due to the unresolved M-shell satellites and to the QED are found to be much smaller than the Breit terms and comparable to the experimental accuracy.

The deuteron binding energy and the neutron mass

A new value for the deuteron binding energy of S(d)=2.38817007(42)×10 −3 u is reported based on an absolute wavelength determination of the 2.2 MeV n–p capture gamma-ray using a crystal diffraction spectrometer. A new more precise value for the neutron mass m n=1.00866491637(82) u is obtained by summing this binding energy and the 2H− 1H mass difference.

Experimental widths of Kα x-ray lines in solid-state 3d elements

Using a high-resolution x-ray crystal diffraction spectrometer, x-ray line widths of the Kα1,2 lines of Fe, Co, Ni and Cu were analysed. Thereby, an evolutionary strategy was used for spectrum deconvolution to determine the life-time governed contributions to the line widths. On this basis, L2–L3X Coster–Kronig widths are calculated and assumptions about the energetics of radiationless transitions are derived. © 1998 John Wiley & Sons, Ltd.

High resolution wavelength dispersive X-ray spectroscopy for ECR plasma diagnostics

The high resolution of a Bragg crystal diffraction spectrometer was used to investigate the ion charge distribution of krypton ions inside the plasma of an 14.5 GHz ECR ion source. Analyzing the measured spectra, we got information about the abundances and the relative densities of krypton ions of different charge states.

Luminosity of Bragg Crystal Diffraction Spectrometers with Flat and Focusing Crystals

Analytical approximations for calculations of the luminous efficiency of Bragg crystal diffraction spectrometers with flat and focussing crystals are derived. The given approximative formulas are in good agreement with ray-tracing calculations presented in an earlier work. Influences of the geometric source dimensions on the luminous efficiency are discussed for both spectrometer types mentioned.