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  • 1990-1994  (6)
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Material
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Year
  • 1
    Electronic Resource
    Electronic Resource
    A neutron TOF investigation of dynamical reflectivity of elastically deformed crystals (1991)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 47 (1991), S. 166-169 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Neutron diffraction in both an absorbing InSb crystal and a non-absorbing Si crystal deformed by a temperature gradient has been investigated experimentally. The observed variation of diffracted intensities with the magnitude and direction of the deformation gradient was compared with results of calculations based on quasi-classical formulas recently reported. A good quantitative agreement was observed in the whole range between the dynamical (perfect crystal) and the kinematical (an ideally imperfect one) limits. At the same time, the possibility of accurate intensity measurements by the TOF method in the wavelength range 0.5–3.0 Å was demonstrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767390011667
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Extinction effects in polarized neutron diffraction from magnetic crystals. I. Highly perfect MnP and YIG samples (1991)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 47 (1991), S. 770-775 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Wavelength-dependent flipping-ratio data obtained with polarized neutrons are analysed with the help of two extinction models: Kato's [Acta Cryst. (1980), A36, 763–769, 770–776] statistical dynamical theory (SDT) and the random elastic deformation (RED) approach [Kulda (1987). Acta Cryst. A43, 167–173; (1991). Acta Cryst. A47, 775–779]. Because the crystals used were nearly perfect, Pendellösung oscillations are present in all cases and the extinction theories are thus tested under extreme conditions. Both treatments give fair agreement with the experimental data in the short-wavelength range and there is no significant difference between them in terms of the goodness of fit, but the parameters involved in the RED approach have a more straightforward physical meaning. There are, however, inconsistencies in the values of the SDT parameters obtained, as well as probable deviations at large wavelength and crystal thickness, which could be related to a new validity condition for SDT.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767391006840
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Neutron diffraction by an absorbing vibrating InSb crystal (1992)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 48 (1992), S. 72-73 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Following our recent paper [Lukáš, Kulda, Mikula, Sedláková, Alexandrov & Vrána (1991). Acta Cryst. A47, 166–169], a comparison of the dynamical description of diffraction by an absorbing elastically deformed perfect crystal with the experimental data taken at diffraction by a longitudinally vibrating InSb crystal is presented. The comparison is performed on the time-dependent integrated intensity spectra for different values of the vibration amplitudes. The applicability of the analytical formulas derived earlier by two of the authors for an arbitrary homogeneous deformation is in this case fully approved by the good agreement between the theory and the experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S010876739100627X
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    The RED extinction model. III. The case of pure primary extinction (1991)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 47 (1991), S. 775-779 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Bragg diffraction in nearly perfect crystals is treated within the framework of the random elastic deformation (RED) model. Similar to the previous applications it is again assumed that each individual reflection event takes place within an elastically deformed domain and hence may be described by either an exact or a quasiclassical solution to the Takagi–Taupin equations. But because of the high degree of perfection and/or small thickness of the crystal the interaction is confined to one single domain so that the total reflected intensity is obtained just by summing up the contributions from the whole ensemble of domains characterized by different values of the deformation gradient and thickness. The present approach profoundly differs from Kato's statistical dynamical theory which starts with the averaging procedure within the Takagi–Taupin equations before solving them.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767391006852
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Direct determination of the SANS contrast factor by neutron interferometry (1990)
    Springer
    Czechoslovak journal of physics 40 (1990), S. 697-699 
    Details
    ISSN: 1572-9486
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01597866
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Neutron backscattering on vibrating silicon crystals-experimental results on the neutron backscattering spectrometer IN10 (1993)
    Springer
    The European physical journal 90 (1993), S. 143-153 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Neutron backscattering on vibrating silicon crystals has been measured in transmission geometry on the backscattering spectrometer IN10 at the Institute Laue-Langevin (ILL). The crystals were excited into longitudinal mechanical resonance vibrations by LiNbO3 transducers glued to the crystal surface. The transmitted intensity of the 111 Bragg reflection was measured as a function of the deformation amplitude at vibration frequencies from 2.5 MHz to 30 MHz. By vibrating the initially perfect silicon crystal, an increase in ΔE/E of the diffracted profile was achieved, accompanied by an increase of the backreflected intensity. The width of the reflection and the resolution is a linear function of the ultrasonic strain over a wide range of excitation strengths. ΔE/E can be easily tuned in a reproducible way by varying the voltage on the piezoelectric transducer. For the highest excited ultrasonic strain an increase of the backscattered intensity of about a factor of 50 is observed. Sound wave amplitudes can be determined from the measured width in ΔE/E of the transmission curves. The obtained results are relevant for the design and operation of intensity-to-resolution tunable monochromators for high resolution instruments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02198147
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    Paper (German National Licenses)
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