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A diffracted-beam monochromator for long linear detectors in X-ray diffractometers with Bragg-Brentano parafocusing geometry
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10.1063/1.4798547
/content/aip/journal/rsi/84/4/10.1063/1.4798547
http://aip.metastore.ingenta.com/content/aip/journal/rsi/84/4/10.1063/1.4798547

Figures

Image of FIG. 1.
FIG. 1.

(a) The diffractometer system, the plane of the drawing coincides with the equatorial plane. The center of the specimen is denoted by C; the monochromator (with the length AB and the center D) is positioned such that diffraction occurs in the axial plane. The inset CDE shows the radius of curvature of the monochromator CD at its center. (b) Axial view of the setup. The cone shape of the monochromator is described by the imaginary axis (TC) and the opening angle β (determined by diffraction angle θmono). The surface of the monochromator crystal is part of this cone.

Image of FIG. 2.
FIG. 2.

Sketch of the axial view of the Soller slit system in front of the monochromator, the axial divergence of the beam is limited by the acceptance angle αs of the Soller slit, αs is determined by the length (L) of the foils and the spacing (w) between the individual foils. For clarity the number of foils of the Soller slit is strongly reduced.

Image of FIG. 3.
FIG. 3.

The efficiency of the diffracted-beam monochromator is estimated from the intensity of the Kα1/Kα2 doublet of the {311} reflection of α-Al2O3 (corundum). The intensity reduction by the monochromator is about a factor of 5. The data obtained with the monochromator are scaled to the net peak intensity of the {311} reflection obtained with Kβ filter.

Image of FIG. 4.
FIG. 4.

Diffraction patterns of the two-phased TRIP steel with monochromator and with Kβ-filter (without monochromator), Soller slit: α s = 2.6°. The reflections of ferrite (α) and austenite (γ) are indexed. The monochromator strongly suppresses the background that is mainly caused by the fluorescence of Mn and Fe in the steel. The data obtained with the monochromator are scaled to the net peak intensity of the {110} reflection obtained with Kβ filter.

Image of FIG. 5.
FIG. 5.

(a) Diffraction pattern of LaB6 with monochromator and with Kβ-filter (without monochromator), Soller slit: αs = 2.6°. The monochromator largely suppresses the low angle background that is mainly caused by air scatter. (b) Suppression of the unwanted {110} Kβ and {200} Kβ reflections for different opening angles of the Soller slits, from top to bottom, αs = 2.6° Kβ-filter (no monochromator), αs = 2.6° with monochromator, αs = 1.5° with monochromator. The data obtained with the monochromator are scaled to the net peak intensity of the {110} reflection obtained with Kβ filter.

Image of FIG. 6.
FIG. 6.

The effect of the monochromator on the angular resolution is illustrated by the FWHM of the individual LaB6 reflections.

Image of FIG. 7.
FIG. 7.

The FWHM and the net intensity of the {311} LaB6 reflection as a function of the axial height slit size. By increasing the slit size the net intensity increases significantly whereas the angular resolution is only slightly reduced.

Image of FIG. 8.
FIG. 8.

(a) Effect of the Soller slits acceptance angle on the background suppression of the TRIP steel specimen. Axial height slit of 8 mm is used. (b) Schematic of the diffracted and fluorescent radiation and the transmitted intensity profiles for Soller slits with acceptance angle 1.5° and 2.6°. Note: Intensities are not to scale.

Tables

Generic image for table
Table I.

Main elements (>0.15 wt. %) in the TRIP steel specimen in wt. % as determined by XRF analysis.

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/content/aip/journal/rsi/84/4/10.1063/1.4798547
2013-04-02
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: A diffracted-beam monochromator for long linear detectors in X-ray diffractometers with Bragg-Brentano parafocusing geometry
http://aip.metastore.ingenta.com/content/aip/journal/rsi/84/4/10.1063/1.4798547
10.1063/1.4798547
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