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Energy Dispersive X-Ray Spectrometry

Description: Abstract: Energy-dispersive x-ray analysis with gas proportional detectors has been used widely in x-ray spectrochemical analysis. It was particularly useful in the detection of low-energy x-ray emission, before the commercial availability of the Blodgett-Langmuir pseudocrystals. With the development of solid-state x-ray detectors of high resolution, and improvement in associated electronics and computers, the interest in energy-dispersive x-ray analysis has increased enormously, to the point where it has replaced Bragg crystal diffraction spectrometry in many instances.
Date: March 1981
Creator: Heinrich, Kurt F. J.; Newbury, Dale E.; Myklebust, R. L. & Fiori, C. E.
Partner: UNT Libraries Government Documents Department

K-Shell Ionization Cross Sections of Selected Elements from Fe to As for Proton Bombardment from 0.5 to 2.0 MeV

Description: The problem with which this investigation is concerned is that of making experimental measurements of proton-induced K-shell x-ray production cross sections and to study the dependence of these cross sections upon the energy of the incident proton. The measurements were made by detection of the characteristic x-rays emitted as a consequence of the ionization of the K-shell of the atom. The method for relating this characteristic x-ray emission to the x-ray production cross section is discussed in this work.
Date: December 1973
Creator: Lear, Richard Dean
Partner: UNT Libraries

Recent x-ray observations of intermediate BL Lac objects

Description: We present recent ROSAT, ASCA and SAX observations of intermediate BL Lac objects (IBLs), i.e. BL Lacs which are located between high-energy and low-energy peaked BL Lac objects with respect to log (S<sub>x</sub>/S<sub>r</sub>). Both, the statistical properties of IBLs from the RGB sample and a detailed broad band X-ray spectral analysis of two objects (1424+2401, 1055+5644), point towards a continuous distribution of synchrotron emission peak frequencies among BL Lac objects.
Date: June 1, 1998
Creator: Brinkmann, W; Laurent-Muehleisen, S & Siebert, J
Partner: UNT Libraries Government Documents Department

Development of a High Resolution X-Ray Imaging Crystal Spectrometer for Measurement of Ion-Temperature and Rotation-Velocity Profiles in Fusion Energy Research Plasmas

Description: A new imaging high resolution x-ray crystal spectrometer (XCS) has been developed to measure continuous profiles of ion temperature and rotation velocity in fusion plasmas. Following proof-of-principle tests on the Alcator C-Mod tokamak and the NSTX spherical tokamak, and successful testing of a new silicon, pixilated detector with 1 MHz count rate capability per pixel, an imaging XCS is being designed to measure full profiles of Ti and vφ on C-Mod. The imaging XCS design has also been adopted for ITER. Ion-temperature uncertainty and minimum measurable rotation velocity are calculated for the C-Mod spectrometer. The affects of x-ray and uclear-radiation background on the measurement uncertainties are calculated to predict performance on ITER.
Date: January 29, 2008
Creator: Hill, K. W.; Broennimann, Ch; Eikenberry, E F; Ince-Cushman, A; Lee, S G; Rice, J E et al.
Partner: UNT Libraries Government Documents Department

X-ray and vibrational spectroscopy of manganese complexes relevant to the oxygen-evolving complex of photosynthesis

Description: Manganese model complexes, relevant to the oxygen-evolving complex (OEC) in photosynthesis, were studied with Mn K-edge X-ray absorption near-edge spectroscopy (XANES), Mn Kb X-ray emission spectroscopy (XES), and vibrational spectroscopy. A more detailed understanding was obtained of the influence of nuclearity, overall structure, oxidation state, and ligand environment of the Mn atoms on the spectra from these methods. This refined understanding is necessary for improving the interpretation of spectra of the OEC. Mn XANES and Kb XES were used to study a di-(mu)-oxo and a mono-(mu)-oxo di-nuclear Mn compound in the (III,III), (III,IV), and (IV,IV) oxidation states. XANES spectra show energy shifts of 0.8 - 2.2 eV for 1-electron oxidation-state changes and 0.4 - 1.8 eV for ligand-environment changes. The shifts observed for Mn XES spectra were approximately 0.21 eV for oxidation state-changes and only approximately 0.04 eV for ligand-environment changes. This indicates that Mn Kb XES i s more sensitive to the oxidation state and less sensitive to the ligand environment of the Mn atoms than XANES. These complimentary methods provide information about the oxidation state and the ligand environment of Mn atoms in model compounds and biological systems. A versatile spectroelectrochemical apparatus was designed to aid the interpretation of IR spectra of Mn compounds in different oxidation states. The design, based on an attenuated total reflection device, permits the study of a wide spectral range: 16,700 (600 nm) - 225
Date: May 16, 2001
Creator: Visser, Hendrik
Partner: UNT Libraries Government Documents Department

High Gain, Fast Scan, Broad Spectrum, Parallel Beam Wavelength Dispersive X-ray Spectrometer for SEM

Description: Parallax Research, Inc. proposes to produce a new type of x-ray spectrometer for use with Scanning Electron Microscopy (SEM) that would have the energy resolution of WDS and the ease of use of EDS with sufficient gain for lower energies that it can be used at low beam currents as is EDS. Parallax proposes to do this by development of new multiple reflection x-ray collimation optics, new diffractor technology, new detector technology and new scan algorithms.
Date: September 12, 2003
Creator: OHara, David & Lochmer, Dr. Eric
Partner: UNT Libraries Government Documents Department

Structure of the Mn complex in photosystem II: Insights from x-ray spectroscopy

Description: We have used Mn K-edge absorption and Kb emission spectroscopies to determine the oxidation states of the Mn complex in the various S-states. We have started exploring the new technique of resonant inelastic X-ray scattering spectroscopy (RIXS); this technique can be characterized as a Raman process that uses K-edge energies (1s to 4p, {approx}6550 eV) to obtain L-edge-like spectra (2p to 3d, {approx}650 eV). The relevance of these data to the oxidation states and structure of the Mn complex is presented. We have obtained EXAFS data from the S0 and S3 states and observed heterogeneity in the Mn-Mn distances, leading us to conclude that there may be three rather than two di-(mu)-oxo bridged units present per tetranuclear Mn cluster. In addition, we have obtained data using Ca/Sr X-ray spectroscopy that provide evidence for a heteronuclear Mn/Ca cluster. The possibility of three di-(mu)-oxo-bridged Mn Mn moieties and the proximity of Ca is incorporated into developing structural models for the Mn cluster. The involvement of bridging and terminal O ligands of Mn in the mechanism of oxygen evolution is discussed in the context of our X-ray spectroscopy results.
Date: April 2, 2002
Creator: Yachandra, Vittal K.
Partner: UNT Libraries Government Documents Department

Probing Reaction Dynamics of Transition-Metal Complexes in Solution via Time-Resolved Soft X-ray Spectroscopy

Description: We report the first time-resolved soft x-ray measurements of solvated transition-metal complexes. L-edge spectroscopy directly probes dynamic changes in ligand-field splitting of 3d orbitals associated with the spin transition, and mediated by changes in ligand-bonding.
Date: May 2, 2010
Creator: Huse, Nils; Kim, Tae Kyu; Khalil, Munira; Jamula, Lindsey; McCusker, James K. & Schoenlein, Robert W.
Partner: UNT Libraries Government Documents Department

Ultrafast conversions between hydrogen bonded structures in liquid water observed by femtosecond x-ray spectroscopy

Description: We present the first femtosecond soft x-ray spectroscopy in liquids, enabling the observation of changes in hydrogen bond structures in water via core-hole excitation. The oxygen K-edge of vibrationally excited water is probed with femtosecond soft x-ray pulses, exploiting the relation between different water structures and distinct x-ray spectral features. After excitation of the intramolecular OH stretching vibration, characteristic x-ray absorption changes monitor the conversion of strongly hydrogen-bonded water structures to more disordered structures with weaker hydrogen-bonding described by a single subpicosecond time constant. The latter describes the thermalization time of vibrational excitations and defines the characteristic maximum rate with which nonequilibrium populations of more strongly hydrogen-bonded water structures convert to less-bonded ones. On short time scales, the relaxation of vibrational excitations leads to a transient high-pressure state and a transient absorption spectrum different from that of statically heated water.
Date: May 1, 2010
Creator: Wen, Haidan; Huse, Nils; Schoenlein, Robert W. & Lindenberg, Aaron M.
Partner: UNT Libraries Government Documents Department

Design Parameters and Objectives of a High-­Resolution X-­ray Imaging Crystal Spectrometer for the Large Helical Device (LHD)

Description: A high-resolution X-ray imaging crystal spectrometer, whose instrumental concept was thoroughly tested on NSTX and Alcator C-Mod, is presently being designed for LHD. The instrument will record spatially resolved spectra of helium-like Ar16+ and provide ion temperature profiles with spatial and temporal resolutions of 1 cm and &gt; 10 ms which are obtained by a tomographic inversion of the spectral data, using the stellarator equilibrium reconstruction codes, STELLOPT and PIES. Since the spectrometer will be equipped with radiation hardened, high count rate, PILATUS detectors,, it is expected to be operational for all experimental conditions on LHD, which include plasmas of high density and plasmas with auxiliary RF and neutral beam heating. The special design features required by the magnetic field structure at LHD will be described.
Date: May 19, 2010
Creator: Bitter, M.; Gates, D.; Neilson, H.; Reiman, A.; Roquemore, A. L.; Morita, S. et al.
Partner: UNT Libraries Government Documents Department

A stored-ion target for x-ray spectroscopy of multicharged ions

Description: With the evolution of the new third generation synchrotron radiation sources providing intense beams of hard x-rays, it is natural to consider exploiting these to investigate the 3-body Coulomb problem. The atomic physics community could advance this field considerably by developing general techniques to investigate the x-ray spectroscopy of heliumlike ions. To do so, however, requires the development of a target of such ions with sufficient density to permit photoexcitation studies in the hard x-ray regime. A possible scheme to achieve this is described. Such a target system would permit x-ray studies with exotic species such as highly charged atomic ions, size-selected cluster ions, and atomic and molecular negative ions which have hitherto been impractical to study with conventional techniques.
Date: August 1996
Creator: Kanter, E. P.
Partner: UNT Libraries Government Documents Department

X-ray absorption studies of battery materials

Description: X-ray absorption spectroscopy (XAS) is ideal for {ital in}{ital situ} studies of battery materials because both the probe and signal are penetrating x rays. The advantage of XAS being element specific permits investigation of the environment of a constituent element in a composite material. This makes it very powerful for studying electrode additives and corrosion of individual components of complex metal hydride alloys. The near edge part of the spectrum (XANES) provides information on oxidation state and site symmetry of the excited atom. This is particularly useful in study of corrosion and oxidation changes in cathode materials during charge/discharge cycle. Extended fine structure (EXAFS) gives structural information. Thus the technique provides both chemical and structural information. Since XAS probes only short range order, it can be applied to study of amorphous electrode materials and electrolytes. This paper discusses advantages and limitations of the method, as well as some experimental aspects.
Date: October 1, 1996
Creator: McBreen, J.
Partner: UNT Libraries Government Documents Department

High resolution x-ray fluorescence spectroscopy - a new technique for site- and spin-selectivity

Description: X-ray spectroscopy has long been used to elucidate electronic and structural information of molecules. One of the weaknesses of x-ray absorption is its sensitivity to all of the atoms of a particular element in a sample. Through out this thesis, a new technique for enhancing the site- and spin-selectivity of the x-ray absorption has been developed. By high resolution fluorescence detection, the chemical sensitivity of K emission spectra can be used to identify oxidation and spin states; it can also be used to facilitate site-selective X-ray Absorption Near Edge Structure (XANES) and site-selective Extended X-ray Absorption Fine Structure (EXAFS). The spin polarization in K fluorescence could be used to generate spin selective XANES or spin-polarized EXAFS, which provides a new measure of the spin density, or the nature of magnetic neighboring atoms. Finally, dramatic line-sharpening effects by the combination of absorption and emission processes allow observation of structure that is normally unobservable. All these unique characters can enormously simplify a complex x-ray spectrum. Applications of this novel technique have generated information from various transition-metal model compounds to metalloproteins. The absorption and emission spectra by high resolution fluorescence detection are interdependent. The ligand field multiplet model has been used for the analysis of K{alpha} and K{beta} emission spectra. First demonstration on different chemical states of Fe compounds has shown the applicability of site selectivity and spin polarization. Different interatomic distances of the same element in different chemical forms have been detected using site-selective EXAFS.
Date: December 1, 1996
Creator: Wang, Xin
Partner: UNT Libraries Government Documents Department

Soft x-ray spectroscopy undulator beamline at the Advanced Photon Source

Description: Construction of the high-resolution soft x ray spectroscopy undulator beamline, 2ID-C, at the Advanced Photon Source (APS) has been completed. The beamline, one of two soft x ray beamlines at the APS, will cover the photon energy range from 500 to 3,000 eV, with a maximum resolving power between 7,000 and 14,000. The optical design is based on a spherical grating monochromator (SGM) giving both high resolution and high flux throughput. Photon flux is calculated to be approximately 10{sup 12}--10{sup 13} photons per second with a beam size of approximately 1 x 1 mm{sup 2} at the sample.
Date: September 1, 1997
Creator: Randall, K.J.; Xu, Z.; Moore, J.F. & Gluskin, E.
Partner: UNT Libraries Government Documents Department

High-resolution X-ray spectroscopy of hollow atoms created in plasma heated by subpicosecond laser radiation

Description: The investigations of ultrashort (0.4-0.6 ps) laser pulse radiation interaction with solid targets have been carried out. The Trident subpicosecond laser system was used for plasma creation. The X-ray plasma emission was investigated with the help of high-resolution spectrographs with spherically bent mica crystals. It is shown that when high contrast ultrashort laser pulses were used for plasma heating its emission spectra could not be explained in terms of commonly used theoretical models, and transitions in so called {open_quotes}hollow atoms{close_quotes} must be taken into account for adequate description of plasma radiation.
Date: October 1, 1997
Creator: Faenov, A.Ya.; Magunov, A.I. & Pikuz, T.A.
Partner: UNT Libraries Government Documents Department

X-ray spectroscopy from fusion plasmas

Description: Our understanding of laser energy coupling into laser-driven inertial confinement fusion targets largely depends on our ability to accurately measure and simulate the plasma conditions in the underdense corona and in high density capsule implosions. X-ray spectroscopy is an important technique which has been applied to measure the total absorption of laser energy into the fusion target, the fraction of laser energy absorbed by hot electrons, and the conditions in the fusion capsule in terms of density and temperature. These parameters provide critical benchmarking data for performance studies of the fusion target and for radiation-hydrodynamic and laser-plasma interaction simulations. Using x-ray spectroscopic techniques for these tasks has required its application to non-standard conditions where kinetics models have not been extensively tested. In particular, for the conditions in high density implosions, where electron temperatures achieve 1 - 2 keV and electron densities reach 10<sup>24</sup> cm<sup>-3</sup> evolving on time scales of < 1 ns, no independent non-spectroscopic measurements of plasma parameters are available. For these reasons, we have performed experiments in open-geometry gas bag plasmas at densities of 10<sup>21</sup> cm<sup>-3</sup> and which am independently diagnosed with Thomson scattering and stimulated Raman scattering. We find that kinetics modeling is in good agreement with measured intensities of the dielectronic satellites of the He-{beta} line (n= l-3) of Ar XVII. Applying these findings to the experimental results of capsule implosions provides additional evidence of� temperature gradients at peak compression.
Date: August 12, 1998
Creator: Glenzer, S H
Partner: UNT Libraries Government Documents Department

Design and performance of the ALS double-crystal monochromator

Description: A new ``Cowan type`` double-crystal monochromator, based on the boomerang design used at NSLS beamline X-24A, has been developed for beamline 9.3.1 at the ALS, a windowless UHV beamline covering the 1-6 keV photon-energy range. Beamline 9.3.1 is designed to simultaneously achieve the goals of high energy resolution, high flux, and high brightness at the sample. The mechanical design has been simplified, and recent developments in technology have been included. Measured mechanical precision of the monochromator shows significant improvement over existing designs. In tests with x-rays at NSLS beamline X-A, maximum deviations in the intensity of monochromatic light were just 7% during scans of several hundred eV in the vicinity of the Cr K edge (6 keV) with the monochromator operating without intensity feedback. Such precision is essential because of the high brightness of the ALS radiation and the overall length of beamline 9.3.1 (26 m).
Date: August 1, 1994
Creator: Jones, G.; Ryce, S.; Perera, R.C.C.; Lindle, D.W.; Karlin, B.A. & Woicik, J.C.
Partner: UNT Libraries Government Documents Department