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Neutron Diffraction Performance Based on Multiple Reflection Monochromator for High-Resolution Neutron Radiography

  • Pavel Mikula
  • Miroslav Vrana
Conference paper

Abstract

The effects of multiple Bragg reflections in single crystal can be observed when more than one set of planes are simultaneously operative for a given wavelength i.e. when more than two reciprocal lattice points are at the Ewald sphere (see e.g. Chang [1]). Multiple reflection effects can result in reducing the intensity of a strong primary reflection or increasing the intensity of a weak primary reflection. The extreme case is the effect of simulation of forbidden primary reflection (often called as Renninger or Umweganregung effect) as first observed Renninger [2] with X-rays and Moon and Shull [3] with neutrons. Using a bent perfect crystal, the multiple reflection effect can be considered as a two step process when primary reflection represented by the lattice planes (h1k1l1]) is simulated by successive reflections realized on the lattice planes (h2k2l2) and (h3k313) which are mutually in dispersive diffraction geometry (Fig. 1). However, it is a common view that dispersive neutron diffraction settings are not convenient for a practical use in an experiment because of low luminosity of a scattering instrument, hi fact, the luminosity corresponds to the volume of the phase space element of the monochromatized beam represented by the wavelength spread Δλ and the divergence Δθ. On the other hand, the dispersive double-crystal reflections can provide very high λ - and θ-resolution making Δλ and Δθ very small without use of any collimators. In relation to the value of the bending radius, the obtained doubly reflected beam has, however, a narrow band-width Δλ/λ of 10-4 -10-3 and Δθ-collimation of the order of minute of arc. It is clear that in comparison with the conventional single reflection monochromators the monochromatic neutron current is lower proportionally to a smaller Δλ and Δθ spread. Recent experimental studies of Mikula et al. [4, 5, 6] proved the possibility of using the multiple reflection

References

  1. 1.
    Chang, Shih-Lin, Multiple Diffraction of X-rays in Crystals, Springer Verlag, Berlin, 1984.CrossRefGoogle Scholar
  2. 2.
    Renninger, M., Zeitschrift für Kristallogr., vol. 113, 99–103, 1960.CrossRefGoogle Scholar
  3. 3.
    Moon, R.M. and Shull, C.G., Acta Crystallographica vol. 17, 805–812, 1964.CrossRefGoogle Scholar
  4. 4.
    Mikula, P., Vrana, M. and Wagner, V., Physica B, vol. 350, e667–e670, 2004.CrossRefGoogle Scholar
  5. 5.
    Mikula et al., In Proceeding 12th International Conference on Experimental Mechanics, Bari, Italy, edited by C. Pappalettere, McGraw-Hill, 2004, CD-ROM-paper 038.Google Scholar
  6. 6.
    Mikula, P., Vrana, M. and Wagner, V., Zeitschrift für Kristallogr. Suppl. 23, 199–204, 2006.Google Scholar

Copyright information

© Springer 2007

Authors and Affiliations

  • Pavel Mikula
    • 1
  • Miroslav Vrana
    • 1
  1. 1.Nuclear Physics Institute and Research Centre Rez Ltd.RezCzech Republic

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