Characteristic X-ray Lines Research Articles

X-ray sources for in situ wavelength calibration of x-ray imaging crystal spectrometers.

X-ray sources for a range of wavelengths are being considered for in situ calibration of X-ray Imaging Crystal Spectrometers (XICSs) and for monitoring line shifts due to changes in the crystal temperature, which can vary during experimental operation over a day [A. Ince-Cushman etal., Rev. Sci. Instrum. 79, 10E302 (2008), L. Delgado-Aparicio etal., Plasma Phys. Control. Fusion 55, 125011 (2013)]. Such crystal temperature dependent shifts, if not accounted for, could be erroneously interpreted as Doppler shifts leading to errors in plasma flow-velocity measurements. The x-ray sources encompass characteristic x-ray lines falling within the wavelength range of 0.9-4.0Å, relevant for the XICSs on present and future fusion devices. Several technological challenges associated with the development of x-ray sources for in situ calibration are identified and are being addressed in the design of multiple x-ray tubes, which will be installed inside the spectrometer housing of the XICS for the JT-60SA tokamak. These x-ray sources will be especially useful for in situ calibration between plasma discharges. In this paper, laboratory experiments are described that were conducted with a Cu x-ray source, a heated quartz (102) crystal, and a pixelated Pilatus detector to measure the temperature dependent shifts of the Cu Kα1 and Kα2 lines at 1.5405 and 1.5443Å, respectively, and to evaluate the 2d-lattice constant for the Bragg reflecting crystal planes as a function of temperature, which, in the case of in situ wavelength calibration, would have to be used for numerical analysis of the x-ray spectra from the plasma.

Application of X-ray principles to quantify sulfur oxidation states in concrete

This study introduces a novel mathematical approach rooted in X-ray spectroscopy principles to evaluate the oxidation state of sulfur, which is then applied in concrete and cementitious materials. Unlike previous studies that relied on an empirical quadratic relationship based on the ratios of characteristic X-ray lines (SKα, SKβ, and SKβ') for sulfur oxidation state determination, unique linear relationships between the intensities of the three X-ray lines for each oxidation state and total sulfur were utilized. Rational equations are then derived by combining these linear relationships for each species. Two independent rational calibration curves are constructed using the SKβ/SKα and SKβ'/SKβ ratios for samples containing sulfide-sulfate mixtures, irrespective of total sulfur concentration within the range of 0.3% to 2.0% by weight of concrete. These equations demonstrated interchangeability across three simulated matrices (Portland cement, concrete, and silica) and two sulfide species (pyrrhotite and pyrite). Absolute quantification of sulfide and sulfate species in concrete is achieved by independently measuring total sulfur. Compared to previous quadratic and linear equations, this approach is shown to minimize the difference between the experimental and calculated ratios of the calibration samples. Agreement was also observed between the sulfate ratio calculated through the rational approach and gravimetric analysis for concrete samples.

Quantification of Unsupported Thin-Film X-ray Spectra Using Bulk Standards.

A quantification model which uses standard X-ray spectra collected from bulk materials to determine the composition and mass thickness of single-layer and multilayer unsupported thin films is presented. The multivariate model can be iteratively solved for single layers in which each element produces at least one visible characteristic X-ray line. The model can be extended to multilayer thin films in which each element is associated with only one layer. The model may sometimes be solved when an element is present in multiple layers if additional information is added in the form of independent k-ratios or model assumptions. While the algorithm is suitable for any measured k-ratios, it is particularly well suited to energy-dispersive X-ray spectrometry where the bulk standard spectra can be used to deconvolve peak interferences in the thin-film spectra. The algorithm has been implemented and made available in the Open Source application National Institute of Standards and Technology DTSA-II. We present experimental data and Monte Carlo simulations supporting the quantification model.

Major and Minor Contributions to X-ray Characteristic Lines in the Framework of the Boltzmann Transport Equation

The emission of characteristic lines after X-ray excitation is usually explained as the consequence of two independent and consecutive physical processes: the photoelectric ionization produced by incoming photons and the successive spontaneous atomic relaxation. However, the photoelectric effect is not the only ionization mechanism driven by incoming photons. It has been recently shown that Compton ionization is another possible process that contributes not negligibly to the ionization of the L and M shells. In addition, the secondary electrons from these two interactions, photoelectric and Compton, are also able to ionize the atom by means of so-called impact ionization. Such a contribution has been recently described, showing that it can be relevant in cases of monochromatic excitation for certain lines and elements. A third mechanism of line modification is the so-called self-enhancement produced by absorption of the tail of Lorentzian distribution of the characteristic line, which mainly modifies the shape of the lines but also produces an intensity increase. The four effects contribute to the formation of the characteristic line and must be considered to obtain a precise picture in terms of the shell and the element. This work furnishes a review of these contributions and their formal theoretical descriptions. It gives a complete picture of the photon kernel, describing the emission of characteristic X-rays comprising the main photoelectric contribution and the three effects of lower extent. All four contributions to the characteristic X-ray line must be followed along successive photon interactions to describe multiple scattering using the Boltzmann transport equation for photons.

Solving the iron quantification problem in low-kV EPMA: An essential step toward improved analytical spatial resolution in electron probe microanalysis—Fe-sulfides

Abstract The use of the field emission gun in scanning electron microscopy permits the imaging of submicrometer-size features. However, achieving sub-micrometer analytical spatial resolution in electron probe microanalysis (EPMA) requires both reducing the electron beam size and reducing the accelerating voltage to achieve the desired sub-micrometer interaction volume. The resulting quantification of the first-row transition metals at low accelerating voltage, i.e., below 7–8 kV, is problematic as the main characteristic X-ray lines (Kα) cannot be excited at these conditions. Furthermore, the use of the Lα and Lβ soft X-ray lines for quantification is complicated by bonding and self-absorption effects resulting in not-yet-determined mass absorption coefficients and hence in the failure of the traditional matrix correction procedure. We propose two methods to circumvent these low-kilovolt (low-kV) analysis limitations: using the non-traditional FeLℓ line and using universal calibration curves for the more traditional FeLα and Lβ lines. These methods were successfully applied to Fe-sulfide minerals showing accurate quantification results by EPMA at reduced kV, necessary for accurate quantification of sub-micrometer sulfide grains.

Low-Voltage Electron-Probe Microanalysis of Uranium.

Electron-probe microanalysis of uranium and uranium alloys poses several problems, such as rapid oxidation, large poorly constrained correction factors, and a large number of characteristic x-ray lines. We show that U-metal can grow 10 nm of oxide within ~20 s of air exposure, increasing to 15–20 nm within a few minutes, which can produce a 30% quantification error at 5 kV. A 15 nm carbon coating on the UO2 reference material also produces an ~30% quantification error of the uncoated but surface oxidized U sample at 5 kV. Correcting for both the coating and oxide improved the analysis accuracy to better than ±1% down to 7 kV and ~2% at 5 kV, but the error increases strongly below this. The measurement of C in U identified a previously unreported U N6–O4 line interference on the C Kα peak, which can produce over 1% error in the analysis total. Oxide stoichiometry was demonstrated to have only a small impact on quantification. The measurement of the O Kα and U Mα mass absorption coefficients in U as 9,528 and 798 cm2/g, respectively, shows good agreement with recently published values and also produces small differences in a quantification error.

A Simple Approach for Thickness Measurements Using Electron Probe Microanalysis.

A simple and fast method for thickness measurements using electron probe microanalysis (EPMA) is described. The method is applicable on samples with a thickness smaller than the electron depth range and does not require any knowledge of instrumental parameters. The thickness is determined by means of the distance that electrons travel inside the sample before crossing through it. Samples are first deposited on a substrate that, when reached by the transmitted electrons, produces an X-ray signal. The measured characteristic X-ray line intensity of the substrate is later used to determine the energy of transmitted electrons, which is proportional to the distance that electrons travel inside the sample. The study was performed on spherical K411 glass particles and cylindrical particles of U–Ce oxide with a size ranging from 0.2 to 4 μm. The measured thicknesses of all the studied particles showed good agreements with the real values. Although the method is only validated on particles with usual shapes, it can be applied to determine a local thickness of thin samples with irregular morphologies. This can help solving multiple issues in analysis with EPMA of non-bulk samples exhibiting complex geometries. Three dimensional microscopic imaging could also find a good utility in the described method.

Screening and selection of XRISM/Xtend flight model CCD

X-ray Imaging Spectroscopy Mission (XRISM) is the next Japanese X-ray astronomical satellite to be launched in 2021 Japanese fiscal year. We are developing one of the XRISM instruments “Xtend”, which is an X-ray CCD camera combined with an X-ray telescope, and achieves the wide field of view of 38′×38′ in 0.4–13keV. In 2019, twelve flight-model (FM) candidate CCD chips were fabricated by Hamamatsu Photonics K.K. We conducted screening experiments to examine whether the FM candidates met requirements for the Xtend CCDs, and selected the four FM chips from them. We constructed a screening system, with which we can examine various CCD performances by illuminating characteristic X-ray lines in a ∼0.5–14keV band or optical lights. With this system, all the twelve candidates were confirmed to satisfy the requirements. We then selected four chips with the best performance, in terms of e.g., their charge transfer inefficiencies, energy resolutions, soft X-ray sensitivities, and optical light leakages. In this paper, we report an overview of the screening system, and procedures and results of the screening process.

Probing cosmic rays with Fe Kα line structures generated by multiple ionization process

Abstract Supernova remnants (SNRs) have been regarded as major acceleration sites of Galactic cosmic rays. Recent X-ray studies revealed neutral Fe Kα line emission from dense gas in the vicinity of some SNRs, which can be best interpreted as K-shell ionization of Fe atoms in the gas by sub-relativistic particles accelerated in the SNRs. In this Letter, we propose a novel method of constraining the composition of particles accelerated in SNRs, which is currently unknown. When energetic heavy ions collide with target atoms, their strong Coulomb field can easily cause simultaneous ejection of multiple inner-shell electrons of the target. This results in shifts in characteristic X-ray line energies, forming distinctive spectral structures. Detection of such structures in the neutral Fe Kα line strongly supports the particle ionization scenario, and furthermore provides direct evidence of heavy ions in the accelerated particles. We construct a model for the Fe Kα line structures by various projectile ions utilizing atomic-collision data.

Ground calibration of Alpha Particle X-ray Spectrometer (APXS) on-board Chandrayaan-2 Pragyaan rover: An empirical approach

Alpha Particle X-ray Spectrometer (APXS) was one of the scientific experiments on-board the Pragyaan rover of the Chandrayaan-2 mission to Moon, with the objective to determine the elemental composition of the lunar surface near the landing site in the south polar region of the Moon. APXS estimates the abundances by measuring the characteristic X-ray lines of the constituent elements present in the target surface, when irradiated by the onboard Cm-244 radioactive source. X-ray spectral measurement in the energy range of 0.8–25 ​keV with an energy resolution of ~135 eV at 5.89 ​keV enables APXS to detect all the major rock-forming elements, such as Na, Mg, Al, Si, Ca, Ti, and Fe. This paper describes the calibration of APXS as an X-ray spectrometer, provides a procedure for quantitative estimation of elemental concentrations based on the measurements of standard geochemical reference materials and provides the detection limits of the major elements. It is shown that, following this procedure, the concentration of the major elements in any sample can be determined with typical accuracy of better than 10% of the actual value.

Angular distribution and polarization of characteristic x-ray lines following innershell photoionization of tungsten by linearly polarized light

The innershell 2p3/2 photoionization of tungsten by linearly polarized light has been investigated, together with the subsequent Lα1 (3d5/2 → 2p3/2) and Lα2 (3d3/2 → 2p3/2) radiative decays. In particular, a specific density matrix formalism is presented for the photoionization and decay process to explore how the linear polarization of the incident ionizing light influences the photoionization process as well as the angular and polarization properties of the emitted characteristic Lα1, 2 photons. Detailed calculations show that the alignment parameter A20 of the 2p3/2 hole state is independent of the polarization of the ionizing photons, while the parameters A2±2 behave proportional to the polarization. It is found that the Lα1, 2 characteristic lines become stronger polarized for linearly polarized incident light with the degree P=−1, when compared with the results in Ref. [Phys. Rev. A 93, 033409 (2016)] for initially unpolarized light, while the characteristic lines become unpolarized for P=1. It is also found that the Lα1, 2 angular distributions are isotropic for the case of P=−1, while they become anisotropic for P=0 and 1.

Investigation of a Contamination Film Formed by the Electron Beam Irradiation

In the study of materials on electron probe devices in the field of action of the electron beam, a contaminating hydrocarbon film is formed, which affects the experimental results. In this paper, we have studied the influence of a contamination film on carbon-film-coated dielectrics on the intensity of cathodoluminescence and characteristic X-ray lines. The absorption coefficient of the contamination film in the visible and UV ranges has been determined. Filming mechanisms at different parameters of the electron beam have been discussed.

Angular and impact energy dependence of intensity ratio of Kα,β x-rays to underneath bremsstrahlung radiation emitted from 15 to 25 keV electrons incident on a pure thick Cu (Z=29) target

We present new results on angular and impact energy dependence of the relative intensity ratios of Kα and Kβ characteristic (CS) x-ray lines to their respective underneath bremsstrahlung (BS) radiation produced from 15-25 keV electrons incident on a thick polycrystalline pure target of Cu (Z = 29). The angular distributions of relative intensity ratios were carried out by measuring the radiations emitted at incidence angle θi that varied from 15° to 75° in reflection geometry mode of the target. The x-rays emerging from the target surface were detected by an energy dispersive Si PIN photodiode detector. The magnitude of relative intensity ratio of Kα/BS is found to be larger than that of Kβ/BS by a factor of about 5.11, 5.24 and 5.49 for 15 keV, 20 keV and 25 keV impact energy, respectively measured, for example, at θi = 15°. However, the intensity ratio of a given characteristic line to its underneath BS increases on average by a factor of about 2.2 in varying the impact energy from 15 keV to 25 keV measured at different angles. The experimental results on angular and impact energy dependence are compared with the corresponding results obtained from Monte-Carlo simulations using the PENELOPE code. The overall agreement between experiment and theory is found to be satisfactory within the uncertainty of measurements.

Compact four-layer Timepix-based particle tracker WidePIX 3D: the first applications in X-ray CT imaging

WidePIX 3D is a compact Timepix-based particle tracking detector with 3D position sensitivity. The device consists of four Timepix chips with 300 μm silicon sensors tightly stacked together. The sensor volume is, therefore, divided into a 3D array of 256 × 256 × 4 voxels. Dual-energy X-ray imaging with sandwich detector is already known as single-shot dual-energy X-ray radiography utilizing a two-layer detector. In the case of WidePIX 3D, the detector can provide up to four sample images produced by different photon spectra from a single exposure. Furthermore, the detection threshold of each layer can be individually adjusted to optimize the resolving performance for elements expected within the scanned sample. In this contribution we present the first results of using the WidePIX 3D detector as an imaging camera for multi-channel energy-sensitive X-ray CT. The procedure of precise threshold-energy calibration of the detector using characteristic X-ray lines will be described and material-resolving CT data will be demonstrated.

Heavy ion PIXE cross sections in Ti, Zn, Nb, Ru and Ta for 4.8–30.0 MeV oxygen and 3.0–12.0 MeV lithium beams

Heavy ion Particle Induced X-ray Emission (PIXE) spectroscopy offers a number of advantages over standard proton PIXE, such as higher yields and therefore higher sensitivity. However, in order to be able to use heavy ion PIXE more detailed measurements of the ionisation and X-ray cross sections for heavy ions are required. This issue was recognised by one of the Coordinated Research Projects (CRP) of the IAEA on MeV Secondary Ion Mass Spectrometry (SIMS). ANSTO took part in this CRP and we measured X-ray production cross sections on a range of samples for oxygen and lithium beam in the energy range of 4.8–30 MeV and 3–12 MeV, respectively. Here we report on these X-ray production cross section measurements and compare the results with theoretical models. Further energy shifts of the characteristic X-ray lines for the different ion-target combinations are presented and discussed.

Combined use of infrared and hard X-ray microprobes for spectroscopy-based neuroanatomy

Understanding the pathological triggers that affect the structural and physiological integrity of biochemical milieu of neurons is crucial to extend our knowledge on brain disorders, that are in many circumstances hardly treatable. Over recently, by using sophisticated hyperspectral micro-imaging modalities, it has been placed within our reach to get an insight into high fidelity histological details along with corresponding biochemical information in a label-free fashion, without using any additional chemical fixatives. However, in order to push forwards extensive application of these methods in the clinical arena, it is viable to make further iterations in novel data analysis protocols in order to boost their sensitivity. Therefore, in our study we proposed a new combined approach utilizing both benchtop Fourier transform infrared (FTIR) and synchrotron X-ray fluorescence (SR-XRF) micro-spectroscopies coupled with multivariate data clustering using the K-means algorithm for combined molecular and elemental micro-imaging, so that these complimentary analytical tools could be used for delineating between various brain structures based on their biochemical composition. By utilizing mid-IR transmission FTIR experiments, the biochemical composition in terms of lipids, proteins and phosphodiesters became accessible. In turn, the SR-XRF experiment was carried out at the advanced IAEA X-ray spectrometry station at Elettra Sincrotrone Trieste. By measuring in vacuum and by using the primary exciting X-ray beam, monochromatized to 10.5 keV, we took advantage of accessing the characteristic X-ray lines of a variety of elements ranging from carbon to zinc. Herein, we can report that the developed methodology has high specificity for label-free discriminating between lipid- and protein-rich brain tissue areas.

Gamma-ray line diagnostics of supernova explosions - SN2014J and Cas A

Gamma-rays from nuclear de-excitation of newly procuced isotopes during supernovae (SNe) provide a unique window to the explosion mechanisms. SNe interiors are accessible only by γ-rays as they are energetic enough to penetrate the SN cloud. Both thermonuclear explosions (type Ia) and core-collapse SNe (CCSN, type II) are key producers of heavy elements in the Universe. In SNe Ia, a white dwarf (WD) is disrupted by ignition from inside or by triggering the explosive event from outside, producing major amounts of 56Ni. Type II SNe are powered by the gravitational collapse of a massive star, having burnt all its nuclear fuel.In this work, we present a diagnostic study of γ-ray lines from SN2014J and Cassiopeia A (Cas A). INTEGRAL observed SN2014J for several months and for the first time, it was possible to measure the characteristic lines from the 56Ni-decay chain in a SN Ia event. Surprisingly, 56Ni was seen only 20 days after the explosion which indicates that some 56Ni must be located outside the WD and not deeply embedded. We provide a 56Co γ-ray line light curve and estimate a visible 56Ni mass of 0.5 M⨀ from a comparison to 1D model light curves. Cas A observations have been revisited and we detect both, the characteristic hard X-ray line from the decay of 44Ti at 78 keV, and the subsequent γ-ray line from the decay of 44Sc at 1157 keV in one coherent data set. Expansion velocities in the range of 2000 − 5000 km s−1 and an initially synthesised 44Ti mass of 1.37 × 10−4 M⨀ are found.

Benefits from bremsstrahlung distribution evaluation to get unknown information from specimen in SEM and TEM

The energy-dispersive X-ray spectrometer (EDS or EDX) is a commonly used device to characterise the composition of investigated material in scanning and transmission electron microscopes (SEM and TEM). One major benefit compared to wavelength-dispersive X-ray spectrometers (WDS) is that EDS systems collect the entire spectrum simultaneously. Therefore, not only are all emitted characteristic X-ray lines in the spectrum, but also the complete bremsstrahlung distribution is included. It is possible to get information about the specimen even from this radiation, which is usually perceived more as a disturbing background. This is possible by using theoretical model knowledge about bremsstrahlung excitation and absorption in the specimen in comparison to the actual measured spectrum. The core aim of this investigation is to present a method for better bremsstrahlung fitting in unknown geometry cases by variation of the geometry parameters and to utilise this knowledge also for characteristic radiation evaluation. A method is described, which allows the parameterisation of the true X-ray absorption conditions during spectrum acquisition. An ‘effective tilt’ angle parameter is determined by evaluation of the bremsstrahlung shape of the measured SEM spectra. It is useful for bremsstrahlung background approximation, with exact calculations of the absorption edges below the characteristic peaks, required for P/B-ZAF model based quantification methods. It can even be used for ZAF based quantification models as a variable input parameter. The analytical results are then much more reliable for the different absorption effects from irregular specimen surfaces because the unknown absorption dependency is considered. Finally, the method is also applied for evaluation of TEM spectra. In this case, the real physical parameter optimisation is with sample thickness (mass thickness), which is influencing the emitted and measured spectrum due to different absorption with TEM measurements. The effects are in the very low energy part of the spectrum, and are much more visible with most recent windowless TEM detectors. The thickness of the sample can be determined in this way from the measured bremsstrahlung spectrum shape.

COMBINED XRD-XRF METHOD OF Fe<sup>2+</sup> DETERMINATION OF IN SINTERS

A method of combined X-ray diffraction-X-ray fluorescence determination of Fe 2+ in medium-basicity agglomerates of ferruginous quartzite ores is proposed. The method is based on measuring the integrated intensity of the magnetite reflex (111) with allowance for the characteristic x-ray lines of the elements that interfere with direct determination of Fe 2+ by x-ray diffraction as a part of the additive intensity correction model. An integrated system ARL 9900 Workstation combines x-ray spectrometer and x-ray diffractometer in a common analytical space. Factors affecting the results of Fe 2+ determination in iron ore agglomerates — change in the absorption coefficient of the sample, formation of magnetite solid solutions, presence of Fe 2+ in the wuestite composition, the amorphous phase, and also in the phases of iron sulfides are considered. The ways of taking them into account which suggest the use of the intensities of characteristic emission x-ray lines of Ti, Mg, Ca, Si and S, as well as the integrated intensities of (200) wustite and (104) hematite reflexes as correction channels are considered. A calibration curve plotted within the concentration range 11.1 – 15.0% illustrates the dependence of the intensity of (111) magnetite reflex on the content of Fe 2+ expressed as oxide. The accuracy and repeatability of the results obtained by combined XRD-XRF method match the requirements of GOST R 53657–2009 standard. The use of the combined x-ray diffraction – x-ray fluorescence method in industrial practice provides significant shortening of the time of determination of the chemical composition of the medium-basicity agglomerates of ferruginous quartzite ores (470 sec for determination of the elemental composition and Fe 2+ , which includes 360 sec for registration of the diffraction data).

A method for lateral localization of a compact gamma source in radionuclide diagnostics

A method for lateral localization of a gamma source in a medium with a miniature single channel scintillation detector is developed and experimentally tested. Method is based on simultaneous registration of two (or more) gamma lines emitted from an area of increased uptake of a radiopharmaceutical in the patients body. The proposed method is tested with the most widely used medical radioisotope technetium-99m which has a 140 keV gamma emission line and a 18 keV characteristic x-ray line. The results of experimental studies show that the lateral coordinate of a point-like 99mTc source can be determined with an accuracy of ± 4 mm at the depth of soft tissues equivalent phantom up to 30 mm.