Evidence for the Fankuchen effect in neutron diffraction by curved crystals

Albertini, G.; Bœuf, A.; Lagomarsino, S.; Mazkedian, S.; Melone, S.; Rustichelli, F.

doi:10.1107/s0567739477000989

Cited by 11 publications

(3 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This arrangement may be used in the large cross section of the incident polychromatic beam and enables us to obtain a high monochromatic beam density. The effect of the spatial condensation of neutrons because of asymmetric Bragg diffraction [originally used by Fankuchen (1937) with a X-ray beam] by elastically bent crystals was first studied in the paper of Albertini, Boeuf, Lagomarsino, Mazkedian, Melone & Rustichelli (1977). Here the authors reported a considerable gain (of about four) in the neutron current density in comparison with the case of the symmetrically cut crystal for ct = 26, fl = 6 °, 2 = 0"18 nm and Si 111 reflection.…”

Section: Introductionmentioning

confidence: 76%

See 1 more Smart Citation

The spatial condensation of the neutron beam by an asymmetric diffraction in thermal-neutron monochromatization

Mikula¹,

Kulda²,

Horalík³

et al. 1986

J Appl Cryst

View full text Add to dashboard Cite

A thermal-neutron monochromator based on an elastically bent perfect silicon crystal in a strongly asymmetric diffraction geometry used for the spatial condensation of the output neutrons is presented and discussed. Its effective 'mosaic spread' 6hO can be easily controlled by a simple choice of the bending radius and the length of the irradiated part of the crystal plate. A theoretical analysis shows that a gain in the flux density of monochromatic neutrons in the fully asymmetric case in comparison with the symmetric one is equal to the ratio of the width of the incident polychromatic beam and the thickness of the crystal. The experimental integrated reflectivity and focusing obtained are found to be in good agreement with theoretical predictions. The asymmetric arrangement of the bent crystal seems to be suitable for use at a source with a large incident-beam cross section when 6hO may achieve a value of about 10-2 rad and an effective neutron flux at the sample position may achieve the fluxes obtained by the best mosaic monochromator.

show abstract

Section: Introductionmentioning

confidence: 76%

“…As in the paper of Albertini, Boeuf, Lagomarsino, Mazkedian, Melone & Rustichelli (1977), let us assume that the regions of the acceptance angles 6oOs and 6o0" corresponding to both geometries are equal. By means of (3) …”

Section: Discussionmentioning

confidence: 99%

The spatial condensation of the neutron beam by an asymmetric diffraction in thermal-neutron monochromatization

Mikula¹,

Kulda²,

Horalík³

et al. 1986

J Appl Cryst

View full text Add to dashboard Cite

show abstract

“…It should be pointed out that one does not expect a loss in the diffracted intensity due to asymmetry as should occur in the case of perfect crystals because the integrated reflectivity of elastically deformed crystals does not depend on the angles between the crystal surface and the incident and reflected beam directions but on the angle between the scattering vector h and the vector of the local displacement of atoms u (Takagi, 1969;Albertini, Boeuf, Lagomarsino, Mazkedian, Melone & Rustichelli, 1977).…”

Section: Theoretical Backgroundmentioning

confidence: 99%

A new version of a medium-resolution double-crystal diffractometer for the study of small-angle neutron scattering (SANS)

Mikula¹,

Lukáš²,

Eichhorn³

1988

J Appl Cryst

View full text Add to dashboard Cite

A new version of a SANS instrument based on two bent perfect Si crystals in the nondispersive (1, -1) setting is presented. Unlike an earlier proposal which employed bent crystals in symmetric diffraction geometry I- Kulda & Mikula (1983). J. Appl. Cryst. 16,[498][499][500][501][502][503][504], use of the crystal analyser in the fully asymmetric geometry enables the angular dependence of the SANS intensity to be transformed into the positional dependence along its longest edge. This makes it possible to employ a one-dimensional position-sensitive detector and thus significantly increase the speed of collection of experimental data. Momentum-transfer resolution may be easily controlled by an adjustment of the bending radii of the crystals. Use was made of diffraction by the (111) crystal planes at a neutron wavelength of 0.2 nm to measure powder samples of Si3N4, poly(vinyl chloride)/poly-(methyl methacrylate) and CrO2 in order to demonstrate the practical efficiency of the proposed device.

show abstract

Study of asymmetric neutron diffraction including the transition from Bragg to Laue case

Eichhorn

Kulda

Mikula

1983

Phys. Stat. Sol. (a)

View full text Add to dashboard Cite

Diffraction properties of a thin silicon single crystal plate are investigated experimentally for both asymmetric Bragg and Laue cases including the transition region between them. The aim is to establish the applicability limits of the conventional dynamical theory and of the more general theory taking into account the curvature of the dispersion surface asymptotes. In the vicinity of the fully asymmetrical position an enhanced role of the end‐face Bragg reflection but no departures from the conventional theory are observed because of the small value of the critical angle θc for total reflection as compared to the generally large beam divergence in the neutron experiments.

show abstract

Evidence for the Fankuchen effect in neutron diffraction by curved crystals

Cited by 11 publications

References 9 publications

The spatial condensation of the neutron beam by an asymmetric diffraction in thermal-neutron monochromatization

The spatial condensation of the neutron beam by an asymmetric diffraction in thermal-neutron monochromatization

A new version of a medium-resolution double-crystal diffractometer for the study of small-angle neutron scattering (SANS)

Study of asymmetric neutron diffraction including the transition from Bragg to Laue case

Contact Info

Product

Resources

About