Angle dispersive diffraction

Fig. 5 Diffraction profiles collected from the same powdered sample of InSb at 2 GPa, using (top) energy- and (bottom) angle-dispersive diffraction. The angle-dispersive data clearly have higher angular resolution, and are not contaminated by X-ray fluorescence peaks. The tick marks below the angle-dispersive data mark the positions of some of the weak superlattice reflections that were essential to determining the structure of the InSb-IV phase [165]...

Yaoita K, Katayama Y, Tsuji K, Kikegawa T, Shimomura O (1997) Angle-dispersive diffraction measnre-ment system for high-pressnre experiments using a multichaimel collimator. Rev Sci lustrum 68 2106-2110... 

Synchrotron X-ray Radiation. Both energy dispersive and angle dispersive diffraction is used for in situ powder diffraction studies using synchrotron X-ray radiation. 

Diffraction spectra of a-quartz, recorded by energy dispersive and angle dispersive detectors, contrasting the different resolutions. The energy dispersive spectrum was recorded in 5 minutes while the angle dispersive record required 54 minutes. 

A 1% solution of spray dried powder in water was prepared and gently stirred with a magnetic stir bar until the powder was completely dispersed. The absence of any clumps when the solution was viewed under a microscope was used as an indicator of complete dispersion. A few mL of solution were placed in the chamber of the Microtrac. In the instrument, the solution flows past a laser beam in an optically clear cell. The angle of diffraction of the laser beam is measured and the size of the emulsion calculated. The calculation is based on the principle that the smaller the emulsion size, the larger the angle of diffraction. The instrument gives results on emulsion size and size distribution as well as calculating the surface area of the emulsion. The entire analysis is computerized. 

Reference wavelengths for calibration lines are corrected from Bearden s values [19] for the recent CODATA determination of lattice spacings and X-ray wavelengths [25]. The dispersion function is fitted to the 10 calibration wavelengths. The dispersion function relates the wavelength of a spectral feature located at the detector centre, to the angle of diffraction measured by clinometers. 

Generally, the x-ray diffraction measurements are made with the incident and diffracted beam passing through the diamond anvils (Fig. 10a) and thus the absorption is typically 25% for MoKa radiation. The Bragg. angle 6 is limited to about 45° and thus either a short wavelength is used or the angle-dispersive mode is preferred, especially in the case of the... 

When m = 0, the angle of the incident radiation is equal to the angle of diffraction, and this corresponds to specular reflection of the incident radiation. When m =, the diffraction is said to be first-order and is the primary image of the spectrum. When m = 2, the diffraction is second-order and is the second image of the spectrum with a dispersion twice that of the first-order, and so forth for higher orders. This may cause interference. Therefore, a filter is used to eliminate higher-order spectra. 

Nelmes RJ, Hatton PD, McMahon MI, Piltz RO, Crain J, Cemik RJ, Bushnellwye G (1992) Angle-dispersive powder-diffraction techniques for eiystal-straeture refinement at high-pressure. Rev Sei Instrum 63 1039-1042... 

The reader may wonder why an energy-dispersed spectrum as shown in Fig. 15-12 does not also contain the various hkl diffraction lines of the specimen, like the energy-dispersive diffraction pattern of Fig. 7-23. After all, the experimental arrangements for diffraction and spectroscopy are similar. Spectra sometimes do contain diffraction lines. Ordinarily, however, they are not observed because spectrometers do not contain collimators. The resulting crossfire of diffracted beams means that the angle 6 is not defined the diffracted radiation is therefore not peaked at particular energies but is merely spread over the background. 

Figure 2.17 Schematic representation of the energy dispersive diffraction (EDD) technique. The energy discriminating detector at fixed scattering angle determines the wavelength of each detected photon and hence the d spacing of the diffracting lattice planes.

Fig. 18. Spectral dispersion at a diffraction grating, a Grating constant, / Blaze angle, t/tp. angle of incident radiation, 2. angle of diffracted radiation with wavelength X.

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