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The optical, photo, and X-ray luminescence properties of Sm3+ ion-doped Li2O-Al2O3-Gd2O3-B2O3-P2O5 glasses are evaluated. The glasses are fabricated by the melt quenching technique. The absorption spectra exhibit the hypersensitive transitions 6H5/2→6P3/2 and 6H5/2→6F7/2 0at the visible and near-infrared range respectively. The glasses display four major transitions characteristic of Sm3+ ion for photoluminescence and X-ray luminescence, with the most intense one corresponding to the 4G5/2→6H7/2 transition. The best emitting samarium concentration obtained by X-ray excitation is compared to BGO crystals. The integral scintillation efficiency of glass is determined by total area under all of peak spectrum. The results indicate the promising application of these glasses in scintillators and for X-ray sensing devices. [ABSTRACT FROM AUTHOR]

A multipurpose imaging x-ray crystal spectrometer is developed for the high energy density instrument of the European X-ray Free Electron Laser. The spectrometer is designed to measure x rays in the energy range of 4–10 keV, providing high-resolution, spatially resolved spectral measurements. A toroidally bent germanium (Ge) crystal is used, allowing x-ray diffraction from the crystal to image along a one-dimensional spatial profile while spectrally resolving along the other. A detailed geometrical analysis is performed to determine the curvature of the crystal. The theoretical performance of the spectrometer in various configurations is calculated by ray-tracing simulations. The key properties of the spectrometer, including the spectral and spatial resolution, are demonstrated experimentally on different platforms. Experimental results prove that this Ge spectrometer is a powerful tool for spatially resolved measurements of x-ray emission, scattering, or absorption spectra in high energy density physics. [ABSTRACT FROM AUTHOR]

2,3,5,6,8,9‐Hexakis(bromomethyl)sumanene, a hexa‐substituted sumanene with bromomethyl groups at the peripheral aromatic carbons, was successfully synthesized in 97% yield with a one‐step reaction. Single‐crystal X‐ray structural analysis showed a formation of a dimer structure. The nucleophilic substitution afforded the introduction of several substituents. These UV‐vis absorption and emission spectra showed clear redshift compared with pristine sumanene, indicating the extension of the conjugation system of hexa‐substituted sumanenes. [ABSTRACT FROM AUTHOR]

In this work, we introduce an indirect X‐ray detector with organic photodiode (OPD). OPD, as a photodetector, is attractive due to its easy fabrication of even large area or flexible form factor. The top electrode of OPD is fabricated with a translucent organic‐metal‐organic (OMO) structure to absorb more light energy by the surface plasmonic effect at the organic‐metal interface. In addition, the new fabricated OPD has a microcavity effect, which is generated between the top and bottom electrodes, makes the broad absorption spectrum of CuPc (active layer) narrower, and tune to the narrow Gd2O2S scintillator emission wavelength. Through X‐ray experiments, the microcavity effect was shown to be useful and controllable by varying the thickness of C60 in the bulk heterojunction (BHJ) structure of the active layers which are composed of C60 and CuPc. [ABSTRACT FROM AUTHOR]

Plant-type ferredoxin (Fd) is an electron transfer protein in chloroplast. Redox-dependent structural change of Fd controls its association with and dissociation from Fd-dependent enzymes. Among many X-ray structures of oxidized Fd have been reported so far, very likely a given number of them was partially reduced by strong X-ray. To understand the precise structural change between reduced and oxidized Fd, it is important to know whether the crystals of oxidized Fd may or may not be reduced during the X-ray experiment. We prepared the thin plate-shaped Fd crystals from Chlamydomonas reinhardtii and monitored its absorption spectra during experiment. Absorption spectra of oxidized Fd crystals were clearly changed to that of reduced form in an X-ray dose-dependent manner. In another independent experiment, the X-ray diffraction images obtained from different parts of one single crystal were sorted and merged to form two datasets with low and high X-ray doses. An Fo–Fo map calculated from the two datasets showed that X-ray reduction causes a small displacement of the iron atoms in the [2Fe-2S] cluster. Both our spectroscopic and crystallographic studies confirm X-ray dose-dependent reduction of Fd, and suggest a structural basis for its initial reduction step especially in the core of the cluster. [ABSTRACT FROM AUTHOR]

In combination with bulky substituents at the core, fourfold benzannulation at the cata‐positions stabilizes a nonacene sufficiently to allow its isolation and characterization by 1H NMR and X‐ray analysis. The four benzo units blueshift the absorption spectrum in comparison to a solely linear nonacene, but significantly increase the stability in the solid state. [ABSTRACT FROM AUTHOR]

Novel azine‐helicene hybrids (pyridine‐, pyrazine‐ and quinoxaline‐fused along the central ring [5]helicenes) have been prepared in good overall yields through a five‐step synthetic sequence. Commercially available 2,3‐dihaloazines were used as starting materials. To discern the effect of merging an azine moiety within a helical skeleton, the X‐ray structures, UV/Vis absorption spectra, cathodic and anodic electrochemistry of the helicene hybrids were investigated and compared to that of the parent [5]helicene. [ABSTRACT FROM AUTHOR]

A silicon detector with a longitudinal silicon wafer has been developed. x-Ray spectra at the K-absorption edges of Au, Pb, and Bi are used to measure its energy resolution. The results are compared with measurements based on x-rays from a 241Am gamma-ray source. The dependence of the energy resolution of the detector on the noise of a charge-sensitive amplifier and on statistical fluctuations in pair production of carriers in the silicon is calculated. [ABSTRACT FROM AUTHOR]

The local structure of a Zn, Sn codoped In2O3 thin film grown on c⁁-plane sapphire by pulsed-laser deposition was examined by polarization-dependent x-ray absorption spectroscopy. The bixbyite film structure is both out-of-plane and in-plane oriented, and the structural results show that both Zn and Sn dopants occupy In sites. The In–O bond length is comparable to that in powder In2O3. However, both Sn–O and Zn–O bonds have two distinct distances in the first shell. Some of the Zn dopants are undercoordinated and, accordingly, some isovalent Sn dopants are overcoordinated for charge balance. In addition, the results suggest that the aliovalent Sn dopants form Frank–Köstlin clusters, (2SnIn•Oi″)x, which provide enough charge carriers to explain the Hall measurements. [ABSTRACT FROM AUTHOR]

Through the full potential linearized augmented plane wave method, we have explored the possibility of defect-induced magnetism in wurtize GaN. The N vacancy defect structure has no sign of a magnetic state. Nonetheless, very interestingly it has been found that the GaN with a Ga vacancy defect can show induced local magnetic moment in N atoms. The four N atoms in the tetrahedron sites neighboring the Ga vacancy have magnetic moments of 0.23 and 0.29μB depending on their positions. The spin-polarized N atoms have a metallic state. It has been observed that the px,y state mainly contributes to the spin polarization of N atoms in the base layer, while the pz state is important for the other N atoms. In addition, the theoretically calculated x-ray absorption spectroscopy and x-ray magnetic circular dichroism of the K edge have been presented. [ABSTRACT FROM AUTHOR]

A micro-x-ray-absorption fine-structure facility based on a monolithic half focusing polycapillary x-ray lens (MHFPXRL), a toroidal mirror, and synchrotron radiation is proposed. The synchrotron radiation is focused by using a combined system of a MHFPXRL and a toroidal mirror. At 8.0 keV, the synchrotron radiation beam with a 2.3×26-mm2 area is first focused into a beam spot with a 0.9×0.3-mm2 area by a toroidal mirror. This focused beam is then focused into a focal spot with a 21.4-μm diameter by using a MHFPXRL. The gain of power flux density in the focal spot of the combined system is 47 473. The focal distance of the MHFPXRL is 13.3 mm. The transmitting extended x-ray-absorption fine-structure (EXAFS) spectrum of Ni foil and the fluorescent EXAFS spectrum of zinc in the zinc hyperaccumulator are measured. [ABSTRACT FROM AUTHOR]

Characteristics of x-ray-induced absorption spectra in various types of synthetic fused silica (SFS) containing 0.1–77×1018 cm-3 of OH were studied up to an irradiation time of 6 h. Induced absorption in the SFS spectra of irradiation with x ray from a Rh target with a dosage of 2×104 C kg-1 h-1 was reproduced by six Gaussian absorption bands, at 3.8, 4.8, 5.0, 5.4, 5.8, and 6.5 eV, respectively. Intensities of these absorption bands increased with power of irradiation time. The intensities of the 5.8, 5.4, and 5.0 eV bands decreased with increasing OH content at an irradiation time shorter than 2 h. At an irradiation time longer than 2 h, on the other hand, the intensities of each absorption band had a minimum at an OH content of ≈5×1018 cm-3, and increased with increasing OH content at higher OH content. The power of the time dependence had a minimum at an OH content of ≈5×1017 cm-3, and increased with increasing OH content for higher OH-containing samples. [ABSTRACT FROM AUTHOR]

Second-order optical nonlinearity was found to be generated in high-purity silica glasses when they were exposed to x-ray radiation and then thermally poled. Two kinds of second-order optical nonlinearity, near-surface nonlinearity localized in a thin layer near the sample surface and bulk nonlinearity spreading throughout the whole sample, were observed. The maximum χ33(2) values of near-surface and bulk nonlinearity were 0.20 and 0.43 pm/V, respectively. Further, a change in refractive index of Δn=4×10-3 was also observed in the sample. The χ33(2) value of the bulk nonlinearity and the change in refractive index increased with the x-ray intensity. On the other hand, the χ33(2) value of the near-surface nonlinearity had a tendency to saturate when the intensity was higher than 1.3 mW/cm2. Based on absorption spectra of the samples, both the bulk nonlinearity and the refractive index change were found to be associated with point defects such as the E′ center (=Si·) and nonbridging oxygen ions (NBO-,=Si–O-). © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on a study on magnetic circular dichroism (MCD) at K and L edges using hard and soft x rays. Introduction to x-ray circular magnetic dichroism; Relation of the MCD properties to x-ray absorption near-edge structure and extended x-ray absorption fine structure regions; Theoretical models; Results.

X-ray absorption spectra of chlorine K edge, ruthenium LIII edge, and rhodium LIII edge from (NH4)3[RhCl6], K3[RuCl6], and [Ru(NH3)6]Cl3 have been measured with a Johann-type 50 cm bent crystal vacuum spectrograph. The white lines due to the transitions to the incompletely filled antibonding molecular orbital (MO) 2t2g(π*) or nonbonding orbital t2g and the empty antibonding MO 3eg(σ*) for the octahedral complexes have been observed in the Cl K edge, Ru LIII edge, and Rh LIII edge regions. It is found that the two absorption peaks at the Ru LIII edge reflect the ligand-field effect. An interpretation for experimental results of the Cl K edge and the Ru LIII edge absorption spectra in K3RuCl6 on the basis of the MO scheme leads us to the conclusion that the white lines at the Cl K edge suffer from the effect of core hole. [ABSTRACT FROM AUTHOR]

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. We show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated by the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 1024 e/cm3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects. [ABSTRACT FROM AUTHOR]

The present study aimed to determine doses delivered to the eye lenses of surgeons while using the inverted-C-arm technique and the protective effect of leaded spectacles during orthopedic surgery. The kerma in air was measured at five positions on leaded glasses positioned near the eye lens and on the neck using small optically stimulated luminescence (OSL) dosemeters. The lens equivalent dose was also measured at the neck using an OSL dosemeter. The maximum equivalent dose to the eye lens and the maximum kerma were 0.8 mSv/month and 0.66 mGy/month, respectively. The leaded glasses reduced the exposure by ~60%. Even if the surgeons are exposed to the maximum dose of X-ray radiation for 5 years, the equivalent doses to the eye lens will not exceed the present limit recommended by the ICRP. [ABSTRACT FROM AUTHOR]

X-ray gas attenuators are used in high-energy synchrotron beamlines as high-pass filters to reduce the incident power on downstream optical elements. The absorption of the X-ray beam ionizes and heats up the gas, creating plasma around the beam path and hence temperature and density gradients between the center and the walls of the attenuator vessel. The objective of this work is to demonstrate experimentally the generation of plasma by the X-ray beam and to investigate its spatial distribution by measuring some of its parameters, simultaneously with the X-ray power absorption. The gases used in this study were argon and krypton between 13 and 530 mbar. The distribution of the 2 p excited states of both gases was measured using optical emission spectroscopy, and the density of argon metastable atoms in the 1 s5 state was deduced using tunable laser absorption spectroscopy. The amount of power absorbed was measured using calorimetry and X-ray transmission. The results showed a plasma confined around the X-ray beam path, its size determined mainly by the spatial dimensions of the X-ray beam and not by the absorbed power or the gas pressure. In addition, the X-ray absorption showed a hot central region at a temperature varying between 400 and 1100 K, depending on the incident beam power and on the gas used. The results show that the plasma generated by the X-ray beam plays an essential role in the X-ray absorption. Therefore, plasma processes must be taken into account in the design and modeling of gas attenuators. [ABSTRACT FROM AUTHOR]

We report X-ray sensing characteristics of a thick n -ZnO film. The film was synthesised using a spin-coating method from a specific solution of zinc acetate dihydrate, ethanol and triethanolamine (TEA). An X-ray diffraction analysis confirmed that the film has crystalline nature having hexagonal crystal structure. The thickness of the film was determined using a scanning electron microscope (SEM) and found to be ∼29–45 µm. An analysis of absorption spectrum revealed the optical bandgap of the sample to be 3.45 eV. The current-voltage (I-V) characteristics were recorded under dark condition and X-ray (at 30 keV, 8 mA) illumination condition. The resistivity of the sensor under the dark condition at bias voltage 2.0 V was found to be 6.4 × 107 Ωcm and that under the X-ray illumination, 4.8 × 106 Ωcm. The sensor shows high signal-to-noise ratio within 0.5–6.0 V bias voltage. The analysis of response time of the sensor shows a rise time of 0.87 s and fall time of 1.08 s at 3.0 V bias voltage. The sensor is also found to be visible blind within 370–700 nm. A quantitative analysis of photoresponse characteristics with dose rate reveals that the sensor shows sublinear response between 0.015 and 0.220 Gy/s. The sensitivity for 0.220 Gy/s dose rate at a bias voltage of V = 6.0 V is found to be ∼ 155.1 μ C. G y − 1 c m − 3 . The sensor shows a pseudo rectifying type I-V characteristic under dark condition. The I-V characteristic under dark condition was further analysed quantitatively using space-charge-limited current (SCLC) model. [Display omitted] • X-ray sensing characteristics of a thick (∼29 – 45 µm) n -ZnO film is reported. • A pseudo rectifying type I-V characteristic is observed under dark condition. • The sensor shows high signal-to-noise ratio within 0.5–6.0 V bias voltage • The sensitivity for 0.220 Gy/s dose rate is found to be ∼ 155.1 μ C. G y − 1 c m − 3 . • The sensor shows rise time of 0.87 s and fall time of 1.08 s at 3.0 V bias voltage. [ABSTRACT FROM AUTHOR]

The EBT3 radiochromic film was introduced as the next generation of EBT and EBT2 films, maintaining the composition of the active layer. X-ray radiation produces a change in its visible light absorption spectrum and optical properties being granted make the films suitable for dosimetric applications. The goal of this study is to present results of absorption spectra measurements for the EBT3 radiochromic film exposed to 6 MV X-ray radiation in the dose range from 0 to 50 Gy. Results showed that the spectrum of the EBT3 radiochromic has an intense band centered at around 636 nm and a less intense centered at around 585 nm. Spectral analysis show that in addition to the two main absorption bands, the absorption spectrum in the spectral range from 400 to 700 nm contains nine more absorption bands. Because to the symmetrical structure of the EBT3 radiochromic film, we assume that the additional absorption bands in the spectral range 400–540 nm are due to an interference pattern that is characteristic of a Fabry-Perot cavity. [ABSTRACT FROM AUTHOR]

Although most of the world's uranium exists as pitchblende or uraninite, this mineral can be weathered to a great variety of secondary uranium minerals, most containing the uranyl cation. Anthropogenic uranium compounds can also react in the environment, leading to spatial-chemical alterations that could be useful for nuclear forensics analyses. Soft X-ray absorption spectroscopy ( XAS) has the advantages of being non-destructive, element-specific and sensitive to electronic and physical structure. The soft X-ray probe can also be focused to a spot size on the order of tens of nanometres, providing chemical information with high spatial resolution. However, before XAS can be applied at high spatial resolution, it is necessary to find spectroscopic signatures for a variety of uranium compounds in the soft X-ray spectral region. To that end, we collected the near edge X-ray absorption fine structure ( NEXAFS) spectra of a variety of common uranyl-bearing minerals, including uranyl carbonates, oxyhydroxides, phosphates and silicates. We find that uranyl compounds can be distinguished by class (carbonate, oxyhydroxide, phosphate or silicate) based on their oxygen K-edge absorption spectra. This work establishes a database of reference spectra for future spatially resolved analyses. We proceed to show scanning X-ray transmission microscopy ( STXM) data from a schoepite particle in the presence of an unknown contaminant. [ABSTRACT FROM AUTHOR]

We study x-ray absorption spectra of azobenzene-functionalized self-assembled monolayers (SAMs), investigating excitations from the nitrogen K edge. Azobenzene with H-termination and functionalized with CF3 groups is considered. The Bethe-Salpeter equation is employed to compute the spectra, including excitonic effects, and to determine the character of the near-edge resonances. Our results indicate that core-edge excitations are intense and strongly bound: their binding energies range from about 6 to 4 eV, going from isolated molecules to densely-packed SAMs. Electron-hole correlation rules these excitations, while the exchange interaction plays a negligible role. [ABSTRACT FROM AUTHOR]

Absorption effects and the impact of specimen shape on TXRF analysis has been discussed intensively. Model calculations indicated that ring shaped specimens should give better results in terms of higher counts per mass signals than filled rectangle or circle shaped specimens. One major reason for the difference in signal is shading effects. Full field micro-XRF with a color X-ray camera (CXC) was used to investigate shading, which occurs when working with small angles of excitation as in TXRF. The device allows monitoring the illuminated parts of the sample and the shaded parts at the same time. It is expected that sample material hit first by the primary beam shade material behind it. Using the CXC shading could be directly visualized for the high concentration specimens. In order to compare the experimental results with calculation of the shading effect the generation of controlled specimens is crucial. This was achieved by “drop on demand” technology. It allows generating uniform, microscopic deposits of elements. The experimentally measured shadings match well with those expected from calculation. [ABSTRACT FROM AUTHOR]

Optical frequency combs have had a remarkable impact on precision spectroscopy. Enabling this technology in the X-ray domain is expected to result in wide-ranging applications, such as stringent tests of astrophysical models and quantum electrodynamics, a more sensitive search for the variability of fundamental constants, and precision studies of nuclear structure. Ultraprecise X-ray atomic clocks may also be envisaged. In this work, an X-ray pulse-shaping method is proposed to generate a comb in the absorption spectrum of an ultrashort high-frequency pulse. The method employs an optical-frequency-comb laser, manipulating the system's dipole response to imprint a comb on an excited transition with a high photon energy. The described scheme provides higher comb frequencies and requires lower optical-comb peak intensities than currently explored methods, preserves the overall width of the optical comb, and may be implemented using currently available X-ray technology. [ABSTRACT FROM AUTHOR]

X-ray grating interferometers produce three distinct signals; an absorption signal, a differential phase signal and a dark field signal. Until now a method for successfully creating dark field tomograms of nonisotropic samples has not been demonstrated. In this paper we test a method for creating such tomograms on a highly nonisotropic sample, i.e. a five layer 'sandwich' of oriented carbon fibers. The fibers are parallel within the individual sandwich layers, but perpendicular to the fibers in the adjacent layers. We show that by choosing a rotation axis parallel to the grating stepping direction (i.e. a horizontal rotation axis in most setup configurations) it is possible to produce a darkfield tomogram where fibers parallel to the probed scattering direction appear to have no dark field signal. The method produces a tomogram in the form of a scalar field of dark field scattering values. [ABSTRACT FROM AUTHOR]

The Z facility at the Sandia National Laboratories is the most energetic terrestrial source of X-rays and provides an opportunity to produce photoionized plasmas in a relatively well characterised radiation environment. We use detailed atomic-kinetic and spectral simulations to analyze the absorption spectra of a photoionized neon plasma driven by the x-ray flux from a z-pinch. The broadband x-ray flux both photoionizes and backlights the plasma. In particular, we focus on extracting the charge state distribution of the plasma and the characteristics of the radiation field driving the plasma in order to estimate the ionisation parameter. [ABSTRACT FROM AUTHOR]

Highlights: [•] Modeling TD-DFT reproduction of X-ray strusctures and absorption spectra. [•] Formulating computationally cheap supporting design of photochemical molecular devices. [•] PDOS prediction of luminescence and non-luminescence in complexes. [Copyright &y& Elsevier]

The first absorption spectra recorded in Europe using synchrotron radiation as the X-ray source were the K-edge of Al and the LIII-edge of Cu taken at Frascati electron synchrotron in May 1963 by the French-Italian group comprised of Y. Cauchois, C. Bonnelle and G. Missoni. [ABSTRACT FROM AUTHOR]

• X-Ray structure of 2-(2-benzofuranyl)-7-hydroxy-1-benzopyrylium perchlorate. • Flavylium form of new benzofuranyl derivatives displays a flat highly conjugated structure. • Structural and electronic characteristics of benzofuranyl-derived flavylium cation, chalcones and chalconates determined from an experimental and theoretical approach. • The fluorescence bands of the flavylium, trans-chalcone and chalconate forms were assigned to their fluorophoric units. In this contribution, we report the synthesis of benzofuranyl-derived flavylium salts whose structure have been confirmed by mass spectrometry and by NMR. Their structural and electronic properties have been studied by absorption and fluorescence spectroscopies and DFT calculations. Theoretical structural parameters of the calculated compounds were validated by the experimentally obtained X-Ray structure of 2-(2-benzofuranyl)-7-hydroxy-1-benzopyrylium perchlorate. The absorption spectra of the benzofuranyl-derived flavylium salts were simulated with good accuracy with respect to the experimental data. In equilibrated buffered solutions, the pH-driven multi-state evolution reaction of novel benzofuranyl-flavyliums afforded trans-chalcone and chalconate derivatives as the predominant species. The elusive nature of the species formed in solution was corroborated by chemical quantum calculations. The fluorescence bands of the flavylium, trans-chalcone and chalconate forms were assigned to their fluorophoric units by selective excitation of each one of the species present in solution. Fluorescence spectroscopy strongly suggests that 2-(2-benzofuranyl)-7-hydroxy-1-benzopyrylium perchlorate displays excited state proton transfer (ESPT). [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Structure of radical anions of “bridged” amidoesters MeOOC(CH2) n CONMe2 (n=0–3) generated by X-ray irradiation was investigated by EPR, optical absorption spectroscopy and quantum-chemical calculations. Amidoester-0 (n=0) has positive calculated electron affinity and the corresponding delocalized radical anion is stabilized independent of matrix polarity. Meanwhile, for amidoesters with n=1–3 groups possessing apparently negative intrinsic electron affinity the role of matrix in stabilization of the corresponding radical anions becomes crucial. Two types of the localized radical anions were observed in the latter case. [Copyright &y& Elsevier]

X-ray data collection for macromolecular crystallography can lead to highly inhomogeneous distributions of dose within the crystal volume for cases when the crystal is larger than the beam or when the beam is non-uniform (Gaussian-like), particularly when crystal rotation is fully taken into account. Here the spatial distribution of dose is quantitatively modelled in order to compare the effectiveness of two dose-spreading data-collection protocols: helical scanning and translational collection. Their effectiveness in reducing the peak dose per unit diffraction is investigated via simulations for four common crystal shapes (cube, plate, long and short needles) and beams with a wide range of full width half maximum values. By inspection of the chosen metric, it is concluded that the optimum strategy is always to use as flat (top-hat) a beam as possible and to either match the beam size in both dimensions to the crystal, or to perform a helical scan with a beam which is narrow along the rotation axis and matched to the crystal size along the perpendicular axis. For crystal shapes where this is not possible, the reduction in peak dose per unit diffraction achieved through dose spreading is quantified and tabulated as a reference for experimenters. [ABSTRACT FROM AUTHOR]

A comprehensive study of size-dependent initial- and final-state effects in 2p x-ray absorption of free, homonuclear 3d transition metal clusters from titanium through nickel in a size range of 1-200 atoms is presented. From atom to bulk the 2p --> 3d excitation in 3d transition metals shifts to higher photon energy, which can be explained by increasing valence electron derealization in the initial state. A cluster-size-dependent decrease of the L2,3 branching ratio at a constant 2p spin-orbit splitting can be attributed to core-hole screening effects for all investigated 3d transition metal clusters. For small manganese cluster ions, highly localized 3d orbitals with ferromagnetic spin coupling and a filled 3d majority spin subband are suggested by the experimental 2/7 x-ray absorption spectra. [ABSTRACT FROM AUTHOR]

This paper reports the absorption spectra of photochromic centers in \CaF2 and \SrF2 crystals doped with \Ce^3+ and \Gd^3+ impurities and thermal decay of the centers in temperature range 80–500 K. The ionized photochromic color centers are generated in crystals under low-temperature X-rays irradiation. These centers are transformed into photochromic color centers upon heating of crystals. All color centers decay at temperature about 500 K. [ABSTRACT FROM PUBLISHER]

First-principles calculations of x-ray absorption spectra (XAS) and the related x-ray magnetic circular dichroism (XMCD) are presented for ultrathin Fe layers on a BaTiO3 (BTO) single-crystal surface within the framework of density functional theory. We have investigated the dependence of XAS and XMCD of Fe L2,3 edges as a function of Fe layer thickness (1-3 ML) and on polarization direction of BTO. The calculations give a detailed insight concerning the relation between structural, electronic, and magnetic properties at the multiferroic interface Fe/BTO. In dependence on the Fe layer thickness we find characteristic features in the related XMCD, which depend strongly on the interface structure. The critical temperature of the ultrathin Fe layer is calculated to be between 170 to 230 K. [ABSTRACT FROM AUTHOR]

Polarization-dependent extended x-ray-absorption fine-structure measurements above the Co-K absorption edge were carried out to experimentally prove the theoretically predicted contraction of interatomic distances in nanoscale Co islands (0 ≈ 1 nm) on Cu(001). Within the Co islands of thickness one monolayer (ML) which were deposited at 160 K substrate temperature, we find an in-plane Co-Co distance of 2.45 ± 0.02 Â, significantly shorter than in bulk Co (2.51 Â) and in close agreement with theoretical predictions. The effective in-plane coordination number N*Co(∥) is equal to 3.2 ± 0.5 and 5.0 ± 0.7 (N* = 6 for an infinite island) for samples covered by 0.3 and 0.7 MLs of Co, respectively. The low value for the 0.3 ML sample is related to the finite island size and to about 20% of the intermixing between the adsórbate and substrate atoms. The experimental results are supported by molecular dynamics calculations. [ABSTRACT FROM AUTHOR]

Background: Portable energy dispersive X-ray fluorescence (pEDXRF) spectrometry analysis was applied for the characterisation of archaeological ceramic findings from three Neolithic sites in Serbia. Two dimension reduction techniques, principal component analysis (PCA) and scattering matrices-based dimension reduction were used to examine the possible classification of those findings, and to extract the most discriminant features. Results: A decision-making procedure is proposed, whose goal is to classify unknown ceramic findings based on their elemental compositions derived by pEDXRF spectrometry. As a major part of decision-making procedure, the possibilities of two dimension reduction methods were tested. Scattering matrices-based dimension reduction was found to be the more efficient method for the purpose. Linear classifiers designed based on the desired output allowed for 7 of 8 unknown samples from the test set to be correctly classified. Conclusions: Based on the results, the conclusion is that despite the constraints typical of the applied analytical technique, the elemental composition can be considered as viable information in provenience studies. With a fully-developed procedure, ceramic artefacts can be classified based on their elemental composition and well-known provenance. [ABSTRACT FROM AUTHOR]

The Schiff base compound (E)-2-[(2-chlorophenyl)iminomethyl]-4-trifluoromethoxyphenol has been synthesized and characterized by IR, UV-vis, and X-ray single-crystal determination. The molecular geometry from X-ray experiment in the ground state has been compared using the density functional theory (DFT) with the 6-311++G(d,p) basis set. The calculated results show that the DFT can well reproduce the structure of the title compound. Using the TD-DFT method, electronic absorption spectra of the title compound have been predicted, and a good agreement is determined with the experimental ones. To investigate the tautomeric stability, optimization calculations at the B3LYP/6-311++G(d,p) level were performed for the enol and keto forms of the title compound. Calculated results reveal that its enol form is more stable than its keto form. The predicted nonlinear optical properties of the title compound are much greater than those of urea. The changes of thermodynamic properties for the formation of the title compound with the temperature ranging from 200 to 500 K have been obtained using the statistical thermodynamic method. At 298.15 K, the change of Gibbs free energy for the formation reaction of the title compound is -824.841 kJ/mol. The title compound can spontaneously be produced from the isolated monomers at room temperature. The tautomeric equilibrium constant is also computed as 3.85 x 10-4 at 298.15 K for enol↔keto tautomerization of the title compound. In addition, a molecular electrostatic potential map of the title compound was performed using the B3LYP/6-311++G(d,p) method. [ABSTRACT FROM AUTHOR]

ABSTRACT GRB 070125 is among the most energetic bursts detected and the most extensively observed so far. Nevertheless, unresolved issues are still open in the literature on the physics of the afterglow and on the gamma-ray burst (GRB) environment. In particular, GRB 070125 was claimed to have exploded in a galactic halo environment, based on the uniqueness of the optical spectrum and the non-detection of an underlying host galaxy. In this work we collect all publicly available data and address these issues by modelling the near-infrared to X-ray spectral energy distribution (SED) and studying the high signal-to-noise ratio Very Large Telescope/FOcal Reducer/low dispersion Spectrograph afterglow spectrum in comparison with a larger sample of GRB absorbers. The SED reveals a synchrotron cooling break in the ultraviolet, low equivalent hydrogen column density and little reddening caused by a Large Magellanic Cloud type or Small Magellanic Cloud type extinction curve. From the weak Mg ii absorption at z= 1.5477 in the spectrum, we derived log N(Mg ii) = 12.96+0.13− 0.18 and upper limits on the ionic column density of several metals. These suggest that the GRB absorber is most likely a Lyman limit system with a 0.03 < Z < 1.3 Z⊙ metallicity. The comparison with other GRB absorbers places GRB 070125 at the low end of the absorption-line equivalent width distribution, confirming that weak spectral features and spectral-line poor absorbers are not so uncommon in afterglow spectra. Moreover, we show that the effect of photoionization on the gas surrounding the GRB, combined with a low N(H i) along a short segment of the line of sight within the host galaxy, can explain the lack of spectral features in GRB 070125. Finally, the non-detection of an underlying galaxy is consistent with a faint GRB host galaxy, well within the GRB host brightness distribution. Thus, the possibility that GRB 070125 is simply located in the outskirts of a gas-rich, massive star-forming region inside its small and faint host galaxy seems more likely than a gas-poor, halo environment origin. [ABSTRACT FROM AUTHOR]

Abstract: A new endstation was developed at beamline 9.3.1 of the Advanced Light Source (ALS), Berkeley, CA, USA, to perform x-ray absorption experiments with soft x-rays on environmental samples such as liquid and hydroscopic solid samples at atmospheric pressure. The sample stage is separated from the vacuum of the beamline by a thin beryllium (Be) window which is 0.05mm thick and 0.64cm in diameter. A Si-photodiode is used to measure fluorescence from the sample. The experiments are conducted in an enclosure (mini-hutch) to protect users from x-ray radiation, to prevent ambient light from hitting the detector, and to allow running experiments with a background of another gas rather than air. Here we report on fluorescent-mode x-ray-absorption measurement at the chlorine K-edge of KCl and CCl3F in liquid and solid phases, illustrating the capabilities of the instrument and the technique. [Copyright &y& Elsevier]

This paper deals with theoretical studies on the 2p-3d absorption in iron, nickel, and copper plasmas related to LULI2000 (Laboratoire pour l'Utilisation des Lasers Intenses, 2000J facility) measurements in which target temperatures were of the order of 20 eV and plasma densities were in the range 0.004-0.01 g/cm³. The radiatively heated targets were close to local thermodynamic equilibrium (LTE). The structure of 2p-3d transitions has been studied with the help of the statistical superconfiguration opacity code SCO and with the fine-structure atomic physics codes HULLAC and FAC. A new mixed version of the SCO code allowing one to treat part of the configurations by detailed calculation based on the Cowan's code RCG has been also used in these comparisons. Special attention was paid to comparisons between theory and experiment concerning the term features which cannot be reproduced by SCO. The differences in the spin-orbit splitting and the statistical (thermal) broadening of the 2p-3d transitions have been investigated as a function of the atomic number Z. It appears that at the conditions of the experiment the role of the term and configuration broadening was different in the three analyzed elements, this broadening being sensitive to the atomic number. Some effects of the temperature gradients and possible non-LTE effects have been studied with the help of the radiative-collisional code SCRIC. The sensitivity of the 2p-3d structures with respect to temperature and density in medium-Z plasmas may be helpful for diagnostics of LTE plasmas especially in future experiments on the Δn = 0 absorption in medium-Z plasmas for astrophysical applications. [ABSTRACT FROM AUTHOR]

The molecular structures of 1, 8-naphthalimide derivatives were investigated at density functional theory level within framework of PBE1PBE/6-31G*. The vertical ionization potential and their delocalization energy of the X-ray solid structure and gas-phase optimized structure were explored. The configuration difference between them was attributed to the π-π interaction of the solid effect, which has negligible effect on their absorption spectra. Solid effect also weakens the intramolecular interaction. Their absorption and luminescent spectra in gas and solvent phase were calculated by time-dependent density functional theory (TDDFT) and conductor polarizable continuum models (CPCM)-TDDFT approaches. Obvious red shifts from the solvent effect were found. Substituents on the imides will not improve their spectra properties a lot, whereas substituents on the naphthalene of naphthalimide would modify their properties to emit different spectra. Systematical deviation of vertical excitation energy from absorption and emission spectra, obtained by CPCM-PBEPBE/6-31G* and CIS-CPCM-PBEPBE/6-31G* models, were about 0.05 eV and 0.02 eV compared with the experimental values. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

Abstract: Chitosans represent a class of functional natural polymers. Their unique attribute is the capability to bind metal ions into their structure. This property can be exploited in many biomedical applications, but before that, some questions about metal binding mechanism must be answered. O-carboxymethyl chitosans with accumulated Fe atoms were studied by X-ray absorption spectroscopy. It was shown that iron bonding depends on the technological processes used in chitosan production. The applied technology allows for the selective introduction of either oxygen alone or of nitrogen and oxygen into the nearest neighbourhood of Fe. Therefore, it is possible to control the surroundings of a metal atom depending on requirements. [ABSTRACT FROM AUTHOR]

The K X-ray absorption near-edge fine structure spectra of metallic Cu, Ni, Co (hexagonal close-packed and face-centered cubic phases), and Cr have been studied. The experimental spectrum of cobalt has been measured in the high-temperature face-centered cubic phase. The calculations have been performed by the full multiple scattering method in the cluster approximation using the semiempirical muffin-tin potential. The spectra have been calculated for clusters containing from 13 to 935 atoms. It has been demonstrated that the spectra cease to depend on the cluster size for clusters containing about 400 atoms. It has been established that the intensity ratio of two peaks located at the fundamental edge of all the spectra under investigation sharply changes with a variation in the atomic potential strength. The mechanisms responsible for the formation of the near-edge structure of the spectra have been revealed using the results of the model calculations. The studies resulted in good agreement of the calculated spectra with the experiment. [ABSTRACT FROM AUTHOR]

Abstract: Natural ilmenites are used all over the world as raw materials in white pigment (TiO2) production. Besides the FeTiO3 in the raw material many other compounds are present. The chemical compounds based on the minority elements influence quality of the final product and are difficult to identify. The knowledge about chemical bonding of the minor elements enables to properly adjust chemical reactions during production processes and to improve quality of the final product. In this paper the X-ray absorption spectroscopy (XAS) identification of the chemical compounds formed by Mg, Mn and Cr in natural ilmenites originating from different places is presented. [ABSTRACT FROM AUTHOR]

copper bromide complex based on benzoin 1′-phthalazinylhydrazone is synthesized. Within density functional theory (OPBE/TZP) the optimal structural parameters of the complex are determined. X-ray Absorption Near-Edge Structure (XANES) spectra above the K absorption edge of copper are measured in the copper bromide complex. Theoretical XANES spectra of the K absorption edge of copper are calculated based on the full multiple scattering method and in the full potential of the finite difference method. Good agreement between the theoretical XANES spectrum and the experimental data is obtained. [ABSTRACT FROM AUTHOR]

A method for x-ray phase contrast imaging is introduced in which only one absorption grating and a microfocus x-ray source in a tabletop setup are used. The method is based on precise subpixel position determination of the x-ray pattern projected by the grating directly from the pattern image. For retrieval of the phase gradient and absorption image (both images obtained from one exposure), it is necessary to measure only one projection of the investigated object. Thus, our method is greatly simplified compared with the phase-stepping method and our method can significantly reduce the time-consuming scanning and possibly the unnecessary dose. Furthermore, the technique works with a fully polychromatic spectrum and gives ample variability in object magnification. Consequently, the approach can open the way to further widespread application of phase contrast imaging, e.g., into clinical practice. The experimental results on a simple testing object as well as on complex biological samples are presented. [ABSTRACT FROM AUTHOR]

Abstract: An apparatus has been designed, built, and patented that is able, non-destructively, to determine bulk density distribution in large-sized ceramic tiles. The proposed method, based on the X-ray absorption technique, provides numerous advantages compared with current methods: it enables complete maps of the bulk density distribution, and is neither destructive nor toxic. The measurements are performed with a low-power X-ray emitter tube. The measurement system is housed in a shielded enclosure. This technique has been used to examine ceramic tiles fabricated under different industrial conditions, modifying press operating parameters. The use of high-precision laser telemeters also enables maps of tile thicknesses to be obtained, which allow tile surface mass to be determined. The non-destructive character of the method enables fired tiles, which had previously been examined in the unfired state, to be inspected, thus facilitating the interpretation of manufacturing defects that could originate in the forming and/or firing stage. [ABSTRACT FROM AUTHOR]

Ziegler-type hydrogenation catalysts, those made from a group 8-10 transition metal precatatyst and an AIR3 cocatalyst are often used for large scale industrial polymer hydrogenation; note that Ziegler-type hydrogenation catalysts are not the same as Ziegler-Natta polymerization catalysts. A review of prior studies of Ziegler-type hydrogenation catalysts (Alley et at. J. Mol. Catal A: Chem. 2010, 315, 1-27) reveals that a ∼50 year old problem is identifying the metal species present before, during, and after Ziegler-type hydrogenation catalysis, and which species are the kinetically best, fastest catalysts-that is, which species are the true hydrogenation catalysts. Also of significant interest is whether what we have termed "Ziegler nanodusters" mm present and what their relative catalytic activity is. Reported hemin is the characterization of an Ir Ziegior-type hydrogenation catalyst, a valuable model (ride infra) for the CO-based industrial Ziegler-type hydrogenation catalyst, made from the crystallographically characterized [(1,5-COD)Ir(μ-O2C8H15)]2 pmcatalyst plus AlEt3. Characterization of this Ir model system is accomplished before and after catalysis using a battery of physical methods including Z-contrast scanning transmission electron microscopy (STEM), high resolution (HR)TEM, and X-ray absorption fine structure (XAFS) spectroscopy. Kinetic studies plus Hg(0) poisoning experiments are then employed to probe which species am the fastest catalysts. The main findings hemin are that (i) a combination of the catalyst precursors [(1,5-COD)Ir(μ-O2C8H15)]2 and AlEt3 gives catalytically active solutions containing a broad distribution of Irn species ranging from monometallic Ir complexes to nanometer scale, noncrystalline Irn nanoclusters (up to Ir∼100 by Z-contrast STEM) with the estimated mean Ir species being 0.5-0.7 nm, Ir∼4-15 clusters considering the similar, but not identical results from the different analytical methods; furthermore, (i) the mean Irn species are practically the same regardless of the Al/Ir ratio employed, suggesting that the observed changes in catalytic activity at different Al/Ir ratios am primarily the result of changes in the form or function of the Al-derived component (and not due to significant AlEt3-induced changes in initial Irn nuclearity). However (iii), during hydrogenation, a shift in the population of Ir species toward roughly 1.0-1.6 nm, fcc Ir(0)∼40-150, Ziegler nanoclusters occurs with, significantly, (iv) a concomitant increase in catalytic activity. Importantly, and although catalysis by discrete subnanometer Ir species is not ruled out by this study, (v) the increases in activity with increased nanociuster size, plus Hg(0) poisoning studies, provide the best evidence to date that the approximately 1.0-1.6 nm, fcc Ir(0)∼40-150, heterogeneous Ziegier nanoclusters are the fastest catalysts in this industrially related catalytic hydrogenation system (and in the simplest, Ockham's Razor interpretation of the data). In addition, (vi) Ziegler nanoclusters are confirmed to be an unusual, hydrocarbon-soluble, highly coordinatively unsaturated, Lewis-acid containing, and highly catalytically active type of nanoclusters for use in other catalytic applications and other areas. [ABSTRACT FROM AUTHOR]

The electronic structure of the (Ge,Mn)Te diluted magnetic semiconductors was investigated theoretically from first principles, using the fully relativistic Dirac linear muffin-tin orbital (LMTO) band structure method. The electronic structure is obtained with the local spin-density approximation (LSDA) as well as the LSDA+U method. The x-ray magnetic circular dichroism (XMCD) spectra of (Ge,Mn)Te DMSs at the Mn L2;3 edges are investigated theoretically from first principles. The origin of the XMCD spectra in the compound is examined. The calculated results are compared with available experimental data. [ABSTRACT FROM AUTHOR]

X-ray photoelectron and absorption spectra have been obtained for natural specimens of cubanite and compared with the corresponding spectra for chalcopyrite. Synchrotron X-ray photoelectron spectra of surfaces prepared by fracture under ultra-high vacuum revealed some clear differences for the two minerals, most notably those reflecting their different structures. In particular, the concentration of the low binding energy S species formed at cubanite fracture surfaces was approximately double that produced at chalcopyrite surfaces. However, the core electron binding energies for the two S environments in cubanite were not significantly different, and were similar to the corresponding values for the single environment in chalcopyrite. High binding energy features in the S 2 p and Cu 2 p spectra were not related to surface species produced either by the fracture or by oxidation, and most probably arose from energy loss due to inter-band excitation. Differences relating to the Fe electronic environments were detectable, but were smaller than expected from some of the observed physical properties and Mössbauer spectroscopic parameters for the two minerals. X-ray absorption and photoelectron spectra together with the calculated densities of states for cubanite confirmed an oxidation state of CuI in the mineral. It was concluded that the best formal oxidation state representation for cubanite is CuI(Fe2)VS. [ABSTRACT FROM AUTHOR]