Characteristic X-ray Research Articles

Techniques for identifying depth inhomogeneities of elemental distribution in materials

X-ray fluorescence analysis (XRF) is a widespread and preferred method for a variety of analytical applications. Among other things, due to its non-invasiveness and non-destructiveness, it is an excellent method for exploring the valuable objects of our cultural heritage. At the same time, however, the fact that it uses relatively low energy X-rays brings some limitations and problems in interpreting the measurement results, especially if objects with inhomogeneous structure are investigated. The depth in the examined material from which characteristic X-rays are detected is in the order of tens to hundreds of μm, depending on the measured element and composition and density of the material. During the development and use of XRF, several procedures have been developed to estimate whether the examined element is distributed homogeneously in the measured layer or has a depth uneven distribution. The least difficult is the measurement under different angles of excitation and excited radiation impact and emission. More sophisticated options are the simultaneous use of Kα and Kβ lines, or K and L lines. The most comprehensive information can be obtained in the confocal arrangement of the spectrometer, where both incident and emitted radiation are narrowly collimated, and the intersection of the two collimated beams is gradually moved under the surface of the object under investigation. The aim of this review paper is to summarize possible procedures for identifying the inhomogeneous structure of the material and test them in the model case of the thickness standards for the copper layer on the steel.

Kossel interferences of proton-induced X-ray emission lines to study thin film waveguides

PIXE combined in Kossel geometry was developed as a non-destructive structural characterization method of nanometer thin films deposited on Si. The method is applied to study Pt/Fe/Pt and Ta/Cr/Pt thin films designed as X-ray planar waveguides. The intensities of characteristic X-ray emissions versus the detection angle (grazing exit), called Kossel curves, were measured by an energy dispersive X-ray camera. It is found that an interfacial compound is formed in Pt/Fe/Pt waveguide, whereas oxidation and mixing occur in the Ta/Cr/Pt system. It was not possible to obtain the description of the successive layers when considering only grazing incidence x-ray reflectivity. When PIXE-Kossel experiments are considered, supplementary constraints have to be fulfilled when fitting the values of the stack parameters (number, composition, thickness, roughness and density of the layers) which restrict the possible descriptions of waveguides. Thus PIXE-Kossel is suitable to characterize stacks of nanometer thin films designed as an x-ray waveguide.

DOSIS: An integrated computational tool for patient-specific dosimetry in nuclear medicine by Monte Carlo and dose point kernel approaches

The use of radiolabeled molecules for tumor targeting constitutes a remarkable technique for the treatment of systemic malignancies. An accurate patient-specific dosimetry in nuclear medicine procedures should be a relevant pre-requisite in order to achieve the required lethal damage to tumor cells while maintaining possible side-effects to normal tissues at tolerable levels. It is desired to assess in vivo the radiopharmaceutical distribution for further estimation of absorbed dose released to target and involved organs. In this context, it was developed a computational toolkit, called DOSIS, in order to perform patient-specific dosimetry based on personalized patient anatomy and biodistribution of radionuclides both obtained by currently available dual PET/CT or SPECT/CT facilities. This work is focused on comparing 3D dose distributions obtained by DOSIS performing full stochastic Monte Carlo simulations versus analogue distributions obtained with analytical approaches like dose point kernel convolution and local energy deposition, when considering non-homogeneous activity or density distributions at different scales. Mathematical virtual phantoms were created for this study in order to compare results with other calculation methods. Some of the beta-emitters radionuclides commonly used for therapy (90Y, 131I, 177Lu) were investigated, and emissions of beta-particles, conversion electrons, gamma radiation, and characteristic X-rays were considered. DOSIS implements a novel code devoted to managing radiation transport simulation by means of PENELOPE Monte Carlo general-purpose routines on voxelized geometries defined by 3D mass and activity distributions. Both distributions can be defined through patients-specific images, or pre-defined virtual phantoms. Results preliminary confirmed DOSIS as a reliable and accurate toolkit for personalized internal dosimetry along with highlighting advantages/drawbacks of the different calculation schemes proposed.

DIAGNOSTIC VALUE OF SPECIFIC IMMUNE COMPLEXES IN DETECTION OF ACTIVE TUBERCULOSIS INFECTION

The diagnostic of tuberculosis infection, including the use of immunological methods, evolved significant changes. The introduction of new diagnostic tests allowed to improve the diagnosis of latent tuberculosis infection (LTI). However, the positive results of immunological tests in both tuberculosis patients and in those with LTI do not allow to divide these conditions, which requires the development and implementation of new diagnostic approaches. Materials and methods . A prospective study with a survey of two groups of patients was conducted: group I (n=50) - patients with verified pulmonary tuberculosis, MBT (+); group II (n =15) – subjects with LTI and control group – healthy subjects (n=14). The examination complex included clinical, radiological, bacteriological, immunological (Mantoux test with 2 TU, T-SPOT.TB, QFT and Diaskintest) methods. Immune complexes were determined in all patients and healthy individuals by the method of dynamic light scattering after the in vitro addition of specific antigens - peptides ESAT-6 and SFP-10. Results . The obtained data demonstrate the low informativeness of the clinical method in the diagnostic of pulmonary tuberculosis. In the presence of characteristic X-ray changes, bacteriological verification of tuberculosis was obtained only in 46% of cases. The use of various immunological tests allows to obtain positive test results in 84-90% of cases simultaneously with the 100% of the positive results in subjects with LTI. Determination of specific immune complexes by the method of dynamic light scattering allows to determine the activity of tuberculosis infection in 100 % of cases and to identify a high-risk group for the development of active tuberculosis in people with latent tuberculosis infection. Conclusions : the obtained data can be applied not only in the diagnosis of active tuberculosis in the absence of diagnosis verification, but also allow to identify a high-risk group for the development of the disease in people with latent tuberculosis infection.

Polyaniline-Cobalt Benzimidazolate Zeolitic Metal-Organic Framework Composite Material for Electrochemical Hydrogen Gas Sensing

The quest for smart sensors with excellent sensitivity, fast response and high reproducibility for hydrogen gas detection has been ongoing for decades. In this work, polyaniline (PANI) was doped with a cobalt-based zeolitic benzimidazolate framework material (CoZIF), to form PANI-CoZIF metal-organic framework (MOF) composite material, which was applied in the electrochemical hydrogen gas sensing. The synthesis of PANI-CoZIF composite was performed by the chemical oxidative polymerization of aniline in the presence of 3.6 wt% CoZIF. The structural properties of the synthesized materials (i.e., PANI, CoZIF, and PANI-CoZIF) were studied by ultraviolet-visible (UV-vis), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Raman spectroscopic analyses, as well as by thermogravimetric analysis (TGA). Scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) and high-resolution transmission electron microscopy/selected area electron diffraction (HR-TEM/SAED) techniques were used for morphological characterization. Both SEM and TEM analyses revealed the grafting of CoZIF on to the surface of PANI in the PANI-CoZIF composite material. XRD patterns and SAED results indicated that PANI and the composite were amorphous in nature. Spectroscopic analyses by FTIR and Raman techniques revealed the coexistence of CoZIF and PANI in the MOF composite material (PANI-CoZIF), which was also confirmed by the high intensities of the characteristic X-ray peaks of ZIF and the polymer. From Tauc plot analysis, it was found that PANI and PANI-CoZIF had band gap energy (Eg) values of 2.5 and 2.3 eV, respectively, indicating that they are both semi-conductors. TGA data confirmed an enhanced thermal stability of PANI-CoZIF compared with pristine PANI. Cyclic voltammetry (CV), chronoamperometry (CA), and Tafel and turn over frequency (TOF) analyses were used to study the electrocatalytic behavior of PANI and PANI-CoZIF in the hydrogen evolution reaction (HER) for gas sensing. There were very significant increases in the TOF value and the magnitude of the catalytic current for PANI-CoZIF compared with pristine PANI as electrocatalysts in the HER. Thus, PANI-CoZIF composite has a greater potential as a suitable electrocatalyst for practical application in the hydrogen fuel technology and hydrogen gas sensing.

Reference-free evaluation of thin films mass thickness and composition through energy dispersive X-ray spectroscopy

In this paper we report the development of a new method for the evaluation of thin films mass thickness and composition based on the Energy Dispersive X-Ray Spectroscopy (EDS). The method exploits the theoretical calculation of the in-depth characteristic X-ray generation distribution function (ϕ(ρz)) in multilayer samples, where ϕ(ρz) is obtained by the numerical solution of the electron transport equation. Once the substrate composition in known, this method gives reliable measurements without the need of a reference sample and/or multiple voltage acquisitions.The electron transport model is derived from the Boltzmann transport equation and it exploits the most updated and reliable physical parameters in order to obtain an accurate description of the phenomenon. The method for the calculation of film mass thickness and composition is validated with benchmarks from standard techniques. In addition, a model uncertainty and sensitivity analysis is carried out and it indicates that the mass thickness accuracy is of the order of 10 μg/cm2, which is comparable to the nuclear standard techniques resolution.We show the technique peculiarities in one example model: two-dimensional mass thickness and composition profiles are obtained for a ultra-low density, high roughness, nanostructured film.

Feasibility study of a new method to measure fast neutron flux by neutron-induced X-ray fluorescence method

A new method is proposed to detect fast neutron flux: the neutron-induced X-ray fluorescence method. In this method, the neutrons are firstly converted to charged particles, and then the charged particles interact with the target to generate the characteristic X-ray fluorescence. Finally, the Kα X-ray emission from the target is detected for measurement of the neutron flux. On the basis of this method, the structure of the detection device is designed: it is composed mainly of a layer of a fast neutron converter and a layer of the target. The Geant4 Monte Carlo simulation toolkit is used to optimize the detection device. According to the simulation results, the detection device is manufactured so as to perform the feasibility verification experiments. In the experiments, a D-T neutron generator is used as the neutron source, and the number of neutrons is changed in two ways: by change of the working voltage of the neutron generator or by change of the measurement time. The experimental results show that there is a good linear relationship between the number of neutrons and the Kα X-ray counts when the measurement time is changed. When the working voltage of the neutron generator is changed, a 3He proportional counter is used as a reference detector. The results show that the trend of the Kα X-ray counts is in good agreement with the trend for the 3He proportional counter. It is proved that this method is feasible for fast neutron flux measurement.

High Speed Matrix Corrections for Quantitative X-ray Microanalysis Based on Monte Carlo Simulated K-Ratio Intensities.

Due to recent advances in modeling the production of characteristic X-rays, Monte Carlo simulation of electron-solid interactions can provide improved quantitative estimates of X-ray intensities for both homogeneous and heterogeneous interaction volumes. In the case of homogeneous materials, these modeled X-ray intensities can predict with excellent accuracy, matrix corrections for arbitrary compositions, arbitrary emission lines, and electron energies. By pre-calculating these Monte Carlo X-ray intensities for pure element standards and a range of compositions of binary systems, we can derive matrix corrections for complex compositions in real-time by parameterizing these k-ratios as the so-called alpha factors. This method allows one to perform Monte Carlo-based bulk matrix corrections in seconds for arbitrary and complex compositions (with two or more elements), by combining these binary alpha factors using the so-called beta expression. We are systematically calculating X-ray intensities for 11 compositions from 1 to 99 wt% for binary pairs of all emitters and absorbers in the periodic table, for the main emission lines (Kα, Kβ, Lα, Lβ, Mα, and Mβ) at beam energies from 5 to 50 keV, using Monte Carlo calculations based on a modified PENELOPE electron-photon transport code, although any other Monte Carlo software could also be utilized. Comparison of k-ratios calculated with the proposed method and experimental k-ratios from the Pouchou and Pichoir database suggest improvements over typical φ(ρz) methods. Additional comparisons with k-ratio measurements from more complex compositions would be ideal, but our testing of the additivity of the beta equation suggests that arbitrary compositions can be handled as well, except in cases of extreme fluorescence or absorption.

The characteristic radiation of copper Kα1,2,3,4.

A characterization of the Cu Kα1,2 spectrum is presented, including the 2p satellite line, Kα3,4, the details of which are robust enough to be transferable to other experiments. This is a step in the renewed attempts to resolve inconsistencies in characteristic X-ray spectra between theory, experiment and alternative experimental geometries. The spectrum was measured using a rotating anode, monolithic Si channel-cut double-crystal monochromator and backgammon detector. Three alternative approaches fitted five Voigt profiles to the data: a residual analysis approach; a peak-by-peak fit; and a simultaneous constrained method. The robustness of the fit is displayed across three spectra obtained with different instrumental broadening. Spectra were not well fitted by transfer of any of three prior characterizations from the literature. Integrated intensities, line widths and centroids are compared with previous empirical fits. The novel experimental setup provides insight into the portability of spectral characterizations of X-ray spectra. From the parameterization, an estimated 3d shake probability of 18% and a 2p shake probability of 0.5% are reported.

Development of non-destructive isotopic analysis methods using muon beams and their application to the analysis of lead

Elemental isotopic ratios are measured in various research fields and provide useful information regarding age, origin, geological and biological activities, ancient climate, etc. Here, we report a new isotopic analysis method without sample destruction using muon-induced characteristic X-rays. We demonstrated this method by conducting muon-beam irradiation experiments on two Pb plates with different isotopic ratios: natural isotopic composition and artificially enriched 208Pb. The observed broad X-ray peaks of the Pb Kα line around 6 MeV were deconvolved with 206Pb, 207Pb, and 208Pb isotopes, giving the isotopic ratios. The resulting isotopic ratios were consistent with those obtained from mass spectrometry.

A re-examination of the fundamental parameters approach to calibration of the Curiosity rover alpha particle X-ray spectrometer

In terrestrial instruments for X-ray emission analysis (e.g. X-ray fluorescence, electron microprobe) the angle of excitation and the angle of characteristic X-ray emission by samples are typically well-defined. This is not the case for the Mars rovers’ alpha particle X-ray spectrometers, necessitating use of “effective” angles in any fundamental parameters approach to spectrum fitting and derivation of element concentrations. A new Monte Carlo computation of expected characteristic X-ray yields has enabled us to examine the choice of effective angles in detail and to compare with our previous estimates; the mean angles taken over all detected events appear to be the most satisfactory approximation. These were used in our GUAPX code to process APXS spectra from ten mono-mineralic geochemical reference materials. Agreement between our concentration values and those determined by the specialist company ActLabs was excellent.

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.

Non-Destructive Determination of Chemical Effects onFluorescence Yields and Vacancy Transfer Probabilities ofTin Compounds

In the current work, it was investigated to the K X-ray fluorescence efficiency and chemical effect on vacancy transfer probability for some tin compounds. We used Br2Tin, TinI2, SeTin, TinF2, TinSO4, TinCl2, TinO and TinS compounds for experimental study. The target samples were irradiated with 241Am annular radioactive source at the intensity of 5 Ci which emits gamma rays at wavelength of 0.2028 nm. The characteristic x-rays emitted because of the excitation are collected by a high-resolution HPGe semiconductor detector. It has been determined that the experimental calculations of the tin (Sn) element are compatible with the theoretical calculation. In addition, we have calculated the experimental intensity ratios, fluorescence yields and total vacancy transfer probabilitiesfor other Sn compounds.

Structural transformation and chemical modifications of the unusual layered zeolite MWW form SSZ-70

SSZ-70 is one of several layered forms of zeolite MMW obtained by direct synthesis with consecutive layers shifted by approximately ±1/3 of a unit cell in the horizontal direction (⟨110⟩), according to the recent structure solution report. Zeolite MWW is a valuable industrial alkylation catalyst and SSZ-70 itself was called by the inventors 'a successful catalytic material'. SSZ-70 shows characteristic powder X-ray diffraction pattern (XRD), containing a unique broad band with a roughly triangular shape and maximum at 8.5–9.0° 2θ (Cu Kα radiation), which can be used to distinguish SSZ-70 from the other MWW materials with different layer arrangements. This work concerns post-synthesis treatments of SSZ-70 to investigate its ability to produce more expanded structures by silylation, swelling and pillaring. Both boron- and aluminum-containing SSZ-70 were investigated. They showed the ability for interlayer expansion by swelling with cationic surfactants and were pillared with silica to produce micro/mesoporous hybrids with increased BET area. Not too surprisingly, the original unique layer stacking of SSZ-70 seems to have become more random and not distinguishable from the swollen forms of the other swellable MWW materials MCM-22 P and the monolayer MCM-56. Calcined SSZ-70 zeolites showed an unusual peak, assigned to (002) reflection, with d-spacing shorter than c-unit cell of the 3D MWW framework, which suggests collapse with formation of the so-called sub-zeolite form. Silylation resulted in different outcomes for B and Al SSZ-70 samples. The former produced interlayer expanded (IEZ) forms of B-SSZ-70 but did not show significant increase in pore volume and BET surface area. Silylation of Al-SSZ-70 did not yield the stabilized (IEZ) form but had a positive effect as it prevented the collapse to sub-zeolite upon calcination. Catalytic testing was carried out for the Al-containing SSZ-70 obtained by direct synthesis and for B-SSZ-70 activated by Al insertion. The former showed much higher concentration of Brønsted acid sites and 5 times faster conversion in a model alkylation reaction between benzyl alcohol and mesitylene. Pillared Al-SSZ-70 showed highest activity despite lower Al concentration due to silica pillars. Both silylation and pillaring had a positive effect on the activity in alkylation reaction with bulky molecules.

Studying the Emission of X-Ray Quanta, Neutrons, and Charged Particles from Deuterated Structures Irradiated with X-Rays

The emission of X-ray quanta, neutrons, and charged particles from deuterated structures under X-ray irradiation is studied. Targets (deuterated chemical-vapor-deposited (CVD)-diamond, palladium, zirconium, and titanium) are irradiated with the use of an X-ray tube equipped with a polycapillary lens with an energy of up to 30 keV and an X-ray tube equipped with a collimator with an energy of up to 25 keV. Different types of detectors, such as a multichannel neutron detector based on He-3 counters, a CR-39 plastic track detector, and silicon surface barrier detectors, are used. The emission of neutrons with an energy of above 10 MeV and alpha particles with an energy range of 7–15 MeV is revealed. This result indicates the possibility of stimulating multiparticle fusion reactions between deuterium nuclei in solid deuterated structures. The analysis of X-ray fluorescence spectra demonstrate the existence of “additional” peaks, which cannot be identified by any characteristic X-ray fluorescence line. Their appearance cannot be associated with any known element or diffraction process. The nature of the origination of the “additional” peaks requires special study.

Simulations of hard X-ray generation by hot electrons in a silver target

A semi-analytical model is developed for the generation of X-ray bremsstrahlung in metallic targets with the inclusion of hot electron recirculation (refluxing). The hard bremsstrahlung and characteristic X-ray yields are calculated in relation to the thickness of a silver target for an s-polarised subpicosecond laser pulse intensity of 2 × 1019 W cm–2. The effect of hot electron recirculation in thin foils is shown to significantly improve the Kα radiation and bremsstrahlung yields in a photon energy of 10 – 100 keV. By contrast, the 0.1 – 1 MeV bremsstrahlung photon yield from thin foils with hot electron recirculation corresponds approximately to the highest photon yield from those targets in which recirculation is insignificant. We make a comparative analysis of the highest laser-to-X-ray energy conversion efficiencies obtained to date.

Study of the X-Ray Radiation in Metal-Containing Composites Irradiated with Neutrons and Photons

Secondary X-ray radiation is studied upon the neutron and photon irradiation of composites. The characteristic X-ray radiation and conversion electrons arising from the capture of slowing neutrons of the DT reaction by liquid-crystal DNA–Gd structures are studied for their effects on biological cells. The liquid-crystal structure in the form of microparticles with a volume of 0.1 µm3 contains 10 000 Gd atoms per DNA molecule. During the neutron irradiation of biological samples with a concentration of 1000 DNA-Gd particles per cell, cells are damaged by secondary radiation at a thermal neutron fluence of ~1011 n/cm2. A high-purity germanium (HPGe) spectrometer is used to study the radiation-protective properties and characteristic X-ray radiation of a Pb-containing composite upon irradiation with photons from cobalt-57 with an activity of 100 kBq.

The X-ray Variability of AGN and its Implications for Observations of Galaxy Clusters

The detection of new clusters of galaxies or the study of known clusters of galaxies in X-rays can be complicated by the presence of X-ray point sources, the majority of which will be active galactic nuclei (AGN). This can be addressed by combining observations from a high angular resolution observatory (such as Chandra) with deeper data from a more sensitive observatory that may not be able to resolve the AGN (like XMM). However, this approach is undermined if the AGN varies in flux between the epochs of the observations. To address this we measure the characteristic X-ray variability of serendipitously detected AGN in 70 pairs of Chandra observations, separated by intervals of between one month and thirteen years. After quality cuts, the full sample consists of 1511 sources, although the main analysis uses a subset of 416 sources selected on the geometric mean of their flux in the pairs of observations, which eliminates selection biases. We find a fractional variability that increases with increasing interval between observations, from about 0.25 for observations separated by tens of days up to about 0.45 for observations separated by $\sim 10$ years. As a rule of thumb, given the precise X-ray flux of a typical AGN at one epoch, its flux at a second epoch some years earlier or later can be predicted with a precision of about $60\%$ due to its variability (ignoring any statistical noise). This is larger than the characteristic variability of the population by a factor of $\sqrt{2}$ due to the uncertainty on the mean flux of the AGN due to a single prior measurement. The precision can thus be improved with multiple prior flux measurements (reducing the $\sqrt{2}$ factor), or by reducing the interval between observations to reduce the characteristic variability.

Grazing-incidence X-ray scattering of lamellar thin films

Recently, surface and thin-film studies using area detectors have become prevalent. An important class of such systems are lamellar thin films formed by small molecules, liquid crystals or semicrystalline polymers. Frequently, the lamellae align more or less parallel to the substrate. Such structures can be easily discerned by their characteristic X-ray scattering close to the incident plane. This paper describes how such patterns can be simulated, in order to extract morphological information about the thin film.

Elementary characterization of Ti metal alloys used in implant dentistry

The main goal of present work is analytical characterization of standard dental implants broadly used by Brazilian dentists. An ideal biological alloy for dental implants must have very high biocompatibility, which means that such material should not provoke any serious adverse tissue response. Dental implants are generally marketed as commercially pure titanium (TiCP) due to their excellent mechanical and physical properties. However, sometimes other alloys are employed and consequently it is essential to study the chemical elements present in those alloys that could bring prejudice for the health. Present work investigated TiCP metal alloys used for dental implant manufacturing and evaluated the presence of elements. For alloy characterization and identification of elements it was used EDXRF technique. This method allows to perform the qualitative and quantitative analysis of the materials using the spectra of the characteristic X-rays emitted by the elements present in the metal samples. The experimental setup was based on two X- ray tubes, Mini X model with Ag and Au targets and X-123SDD detector (AMPTEK) and a 0.5 mm Cu collimator, developed due to specific sample geometrical and topography characteristics. Obtained results showed that implant alloys are not exactly TiCP but were manufactured using Ti-Al-V alloy, which contained Fe, Ni, Cu and Zn. The presence of such metals as Al and V in all studied samples shows very clear that studied implants were not manufactured from TiCP alloy. Moreover, according to the American Society for Testing and Materials (ASTM), these elements should not be present in TiCP.