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  • 1
    Electronic Resource
    Electronic Resource
    Observation of five-fold local symmetry in liquid lead (2000)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 408 (2000), S. 839-841 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The local point symmetry of the short-range order in simple monatomic liquids remains a fundamental open question in condensed-matter science. For more than 40 years it has been conjectured that liquids with centrosymmetric interactions may be composed of icosahedral building blocks. But ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35048537
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  • 2
    Electronic Resource
    Electronic Resource
    Instrument Function in Powder Diffraction (1996)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 29 (1996), S. 617-624 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The instrument function for energy-dispersive powder diffraction and angular-dispersive powder diffraction is presented. The contribution made by sample absorption is included in the instrument function. Both the equatorial and axial divergence functions are calculated in reflection geometry. The axial divergence function is calculated for Soller slits and aperture slits. The equatorial aberrations and the absorption contributions to the line profile are determined for an apparatus with collimator, antiscatter and receiving slits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889896005122
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  • 3
    Electronic Resource
    Electronic Resource
    Profile Function of Bragg Reflections in Powder Diffraction (1996)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 29 (1996), S. 625-631 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The profile function of the Bragg reflection is composed of the contributions of the apparent size and shape of the crystallites, of the strain and of the instrument function. The contribution of the strain is obtained from the displacement distribution of the unit cells. The apparent shape and size of the crystallites and the anisotropy of the strain are presented in terms of spherical harmonics, which are adapted to the symmetry. The apparent crystallite shape and size and strain of Mo (body-centred cubic) and PbBr2 (orthorhombic) are determined from powder diffraction pattern measurements. The calculated line profiles agree closely with the measurements and only a few spherical harmonic terms are needed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889896005134
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  • 4
    Electronic Resource
    Electronic Resource
    High-energy magnetic Compton scattering experiments at ESRF (1998)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 5 (1998), S. 940-942 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Investigations of spin densities in ferromagnetic materials using magnetic Compton scattering are reported. At the high-energy beamline ID15 at the ESRF, experiments have been carried out utilizing the high flux at very high photon energies. Energies from 60 up to 1000 keV have been used for investigations of experimental resolution, cross section, spin moments and momentum distribution. Optimized conditions are found for photon energies from 200 to 250 keV with a momentum resolution 〈 0.4 a.u. and a doubled magnetic effect compared with earlier measurements. In the determination of absolute spin moments multiple scattering has to be taken into account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049597017561
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  • 5
    Electronic Resource
    Electronic Resource
    Characteristic X-ray flux from sealed Cr, Cu, Mo, Ag and W tubes (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 412-417 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The flux of characteristic Kα radiation from sealed X-ray tubes with Cr, Cu, Mo, Ag and W targets is determined on an absolute scale by measuring integrated intensities of Bragg reflections from well characterized powder samples. The values of the flux are corrected for absorption in the tube target. The tube voltage is varied, and the flux is observed to vary as (U0−1)p, where U0 is the ratio of tube voltage to the excitation voltage of characteristic Kα radiation (over-voltage). The exponent p is very close to the theoretical value of 1.67 in the cases of Cr, Cu, Mo and Ag, while in the case of W the value of p is 1.45. The absolute values of the flux are close to the theoretical estimates of Green & Cosslett [Proc. Phys. Soc. (London) (1961), 78, 1206–1214] for Cr and Cu, 10 to 20% higher for Mo and Ag, but only about 1/3 of the calculated flux of W Kα radiation. This is due to an inadequate calculation of the indirect production of characteristic X-rays. A simple formula for the flux per unit solid angle is given in terms of the atomic number of the target, the tube voltage and the K excitation voltage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890006082
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  • 6
    Electronic Resource
    Electronic Resource
    Whole-pattern fitting in energy-dispersive powder diffraction (1992)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 25 (1992), S. 97-104 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A new procedure of pattern decomposition in energy-dispersive powder diffraction is presented. The total observed pattern is taken as a sum of incoherent and coherent scattering. The incoherent part is calculated from theoretical cross sections for individual atoms, the coherent part is described as a sum of discrete Bragg peaks and acoustic and optic phonon thermal diffuse scattering (TDS) is calculated from the Debye and Einstein models, respectively. The total TDS is scaled to be the scattering missing from the Bragg reflections due to thermal motion. The model pattern is convoluted by the instrument function calculated from the diffraction geometry, and the pattern is fitted to the observed one by varying the integrated Bragg intensities and thermal motion parameters. The method is applied to patterns of Mg, Al and Ti powders, leading to an unambiguous and self-consistent division to the background and the pattern of Bragg reflections. As an application, the flux of continuous radiation from a W-anode X-ray tube is determined using theoretical integrated Bragg intensities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891010786
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  • 7
    Electronic Resource
    Electronic Resource
    Determination of thermal-motion parameters using energy-dispersive powder diffraction (1992)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 25 (1992), S. 105-108 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An intrinsic Ge detector is used to analyze the energy spectrum of a well collimated X-ray beam of white radiation diffracted from powder samples of Al, Mg and Ti. Two spectra on each sample are measured at scattering angles where reflections hkl and 2h′ 2k′ 2l occur at the same energies. The Bragg reflections are separated by fitting a model for the different components of scattering to the total spectrum. The thermal-motion parameter B is determined from the intensity ratio of several pairs of reflections. Most of the uncertainties due to a non-ideal sample or errors in the experimental parameters cancel out in the expression for B. The values of B are 0.86 (2) Å2 for Al, Ba = 1.29 (8) Å2 and Bc = 1.60 (9) Å2 for Mg and Ba = 0.63 (4) Å2 and Bc = 0.73 (7) Å2 for Ti, where Ba is for directions perpendicular to the c axis and Bc for the direction of the c axis. The results are in agreement with published values of the thermal-motion parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891010798
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  • 8
    Electronic Resource
    Electronic Resource
    Focusing Optics for High-Energy X-ray Diffraction (1998)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 5 (1998), S. 226-231 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Novel focusing optical devices have been developed for synchrotron radiation in the energy range 40–100 keV. Firstly, a narrow-band-pass focusing energy-tuneable fixed-exit monochromator was constructed by combining meridionally bent Laue and Bragg crystals. Dispersion compensation was applied to retain the high momentum resolution despite the beam divergence caused by the focusing. Next, microfocusing was achieved by a bent multilayer arranged behind the crystal monochromator and alternatively by a bent Laue crystal. A 1.2 µm-high line focus was obtained at 90 keV. The properties of the different set-ups are described and potential applications are discussed. First experiments were performed, investigating with high spatial resolution the residual strain gradients in layered polycrystalline materials. The results underline that focused high-energy synchrotron radiation can provide unique information on the mesoscopic scale to the materials scientist, complementary to existing techniques based on conventional X-ray sources, neutron scattering or electron microscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049598001393
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  • 9
    Electronic Resource
    Electronic Resource
    A focusing multilayer analyser for local diffraction studies (1999)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 6 (1999), S. 979-984 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A novel X-ray diffraction technique for the local structural characterization of thick specimens is presented. Broad energy-band focusing elements are used both on the incoming and exit (diffracted) side of the sample. The geometry allows imaging, and magnification, of a line through the thickness of the sample. In comparison with conventional methods of defining three-dimensional gauge volumes the new technique provides superior depth resolution, higher flux, and a remedy for some systematic errors occurring in strain measurements due to, for example, grain size effects. The technique is validated by a synchrotron test experiment using a bent and meridionally graded multilayer as the focusing analyser element. The incoming beam is monochromated, at 30 keV, and focused to a 15 µm spot size by means of a bent Laue crystal. The resulting depth profile from the (222) reflection of a 21 µm-thick rolled Au foil has a width of 44 µm. The depth resolution, magnification and reflectivity as a function of the energy bandwidth are found to be well matched by theory. The prospect of the technique and the associated aberrations are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049599001934
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  • 10
    Electronic Resource
    Electronic Resource
    Uranium-sensitive tomography with synchrotron radiation (1999)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 6 (1999), S. 1059-1064 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Element-sensitive tomography produces quality information in the field of medical imaging. This method, also known as dichromatic tomography, can be useful to visualize the distribution of heavy elements, such as actinides, without destroying the sample. One of the problems is to obtain a monochromatic photon beam of sufficiently high energy; the other is to have a way of recording these high-energy photons with a good spatial resolution. Here, the results of a first experiment on uranium mapping with synchrotron radiation are reported. Various natural and artificial samples of a few centimetres in size with uranium concentration between 0.008 g cm−3 and 2 g cm−3 were scanned using photon beams around 115 keV and a specially designed camera. The data were then analysed using a conventional fast reconstruction technique. This yielded excellent results with spatial resolutions down to 50 µm. For the first time it was shown that element-sensitive tomography using synchrotron radiation could be extended to the heaviest natural element. Therefore, in principle, the spatial distribution of any element can now be reconstructed using synchrotron radiation. Extension of this technique to very heavy elements can be important for geology, health physics and nuclear waste storage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049599008444
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