Bragg reflections diffraction

Bragg reflection/diffraction point, 40 Brome mosaic virus (BMV), 203 Bromoviridae, 152, 153 BTV. See Bluetongue virus (BTV)... 

Diffraction point. See Bragg reflection/ diffraction point... 

Bragg reflection Diffraction of X rays by a crystal has been shown by W. L. Bragg to be equivalent to reflection from a lattice plane in the crystal. While the term diffracted beam is correct, the term reflection is also used, although the term Bragg reflection is preferable. 

The area detector - is an electronic device for measuring many diffracted intensities at one time. It is an electronic substitute for film, and is now used, where possible, for crystals of biological macromolecules. It is a position-sensitive detector, and is coupled to an electronic device for recording the data in computer-readable form. The data so recorded include the intensity of a Bragg reflection (diffracted beam) and its precise direction (as a location on the detector). Both types of information are needed for each Bragg reflection so that I(hkl), and sinO/X can be determined. 

As one may infer from the quotation, W. L. Bragg realized that a crystal can act as an x-ray grating made up of equidistant parallel planes (Bragg planes) of atoms or ions from which unmodified scattering of x-rays can occur in such fashion that the waves from different planes are in phase and reinforce each other. When this happens, the x-rays are said to undergo Bragg reflection by the crystal and a diffraction pattern results. 

Fig. 4-6. Diffraction of a beam from a point source by a large crystal. The crystal is positioned for the Bragg reflection of wavelength X2 at angle 02 Without a slit, Bragg reflection of all wavelengths between Xi and X3 will occur because the crystal receives x-rays at all angles between 0i and 03. A slit at A or B will collimate the beam and remove the unwanted wavelengths.

Monochromatization by Bragg reflection, see Bragg reflection Monochromators, relation of wavelength to diffraction angle for common, table, 318-327... 

Fig. 2.—Different types of diffracting specimens (a) a single crystal (left) composed of three-dimensionally periodic unit-cells and its diffraction pattern (right) containing Bragg reflections of varying intensities.

Fig. 2. (continued)—(d) an aggregate of microcrystallites whose long axes are parallel, but randomly oriented (left), diffracts to produce a series of layer lines (right) and (e) a polycrystalline and preferentially oriented specimen (left) diffracts to give Bragg reflections on layer lines (right). The meridional reflection on the fourth layer line indicates 4-fold helix symmetry. 

Fig. 4. Schematic representation of the smectic layering along with their characteristic diffraction patterns for the monolayer (Ai), the partially bilayer (Aj), the bilayer (A2) and the two-dimensional (A) phases. The arrows indicate permanent dipoles, the solid points are Bragg reflections...

As has been confirmed by XRD, the framework of montmorillonite has been partly destroyed due to the calcination under high temperature. Most diffraction peaks of montmorillonite are faint. After hydrothermal crystallization the characteristic Bragg reflections for zeolite Beta structure at 7.7° and 22.42° 20 are detected in the composite, indicating the presence of the Beta phase. 

There are established criteria for obtaining b by using diffraction contrast (23). Briefly, the dislocation intensity (contrast) is mapped in several Bragg reflections (denoted by vector, g) by tilting the crystal to different reflections and determining the dot product of the vectors g and b (called the g b product analysis). 

Angular-dispersive X-ray diffraction is used as a standard characterisation technique in the majority of solid-state laboratories. In this method, a constant-wavelength X-ray source is used. A detector sweeps a range of angles, and therefore Bragg reflections are separated by a spatial coordi-... 

When an equimolar solution of the two salts is used, the reaction is shown to be extremely rapid - the host peak had decayed completely before data collection commenced. Bragg reflections with d-spacings of 14.8 and 13.4 A appear in the diffraction pattern, corresponding to the 1,2-BDA and 1,4-BDA intercalates respectively (Fig. 20). 

---