X-ray dispersion

Excitation of sample by bombardment with electrons, radioactive particles or white X-rays. Dispersive crystal analysers dispersing radiation at angles dependent upon energy (wavelength), detection of radiation with gas ionization or scintillation counters. Non-dispersive semiconductor detectors used in conjunction with multichannel pulse height analysers. Electron beam excitation together with scanning electron microscopes. 

Direct measurement of soil is most often carried out on air-dried soil and involves spectroscopic instruments and methods. For example, X-ray dispersion (XRD), X-ray fluorescence (XRF), infrared (IR) spectroscopy,... 

The X-ray intensity diffraction data of the given crystal do not allow one to specify which of the two sets describes the actual crystal structure and thus the absolute configuration of the molecule when there is no effect of anomalous X-ray dispersion. Under such conditions Friedel s law holds, which states that the X-ray intensity diffraction pattern of a crystal is centrosymmetric whether the crystal structure is centrosymmetric or not. This does not mean that a false crystal structure containing a center of symmetry is obtained as the solution of the structural problem, but rather that the X-ray analysis cannot differentiate between the two enantiomeric structures. A simple mathematical analogy is provided by the two possible square roots of a number Vj = x. 

The discoloring is likely to be caused by the photoreduction of silver chloride and/or silver phosphate in the skin. X-ray dispersive analysis of skin and other tissues reveals that the granules consist of silver complexed with sulfur and/or selenium. The photoreduced deposits are not removed by the body, and there are no clinical means of removing them. 

Creagh, D. C. (1999). X-ray dispersion corrections. The International Union of Crystallography, Dordrecht/Boston/London. 

The use of photoresists to cover most of the metal surface and isolate individual pits has made possible detailed analysis of these entities, varying in radius from around 0.1 to 5 pm. The methods of examination include Auger spectroscopy, scanning electron microscopy, X-ray dispersive analysis, and atomic force microscopy (Ke and Alkyre, 1995). 

For many years no attempt was made to determine the absolute stereochemistry of transition metal complexes, although Kuhn (8) calculated the absolute configuration of (—)n-[Co(C204)3]3- from its anomalous optical rotatory dispersion, using classical coupled oscillator theory. He later (9) extended his theory to other tris-chelated cobalt complexes such as (+)n-[Co(en)3]3+. However, in 1955 Saito (10) showed by anomalous X-ray dispersion that Kuhn s suggested configuration for (+)n-[Co(en)3]3+ was incorrect. 

Constantopoulos et al. (1985, 1987a, 1991) attributed the pleural calcifications to the domestic production and use of a tremolite-asbestos-containing whitewash ( luto ) made from a local soil. Analysis of samples of the whitewash material by light microscopy, transmission electron microscopy, and x-ray dispersion analysis indicated that it contained predominantly asbestiform tremolite (Langer et al. 1987). 

The combined use of light microscopy, electron microscopy (transmission and scanning), and x-ray dispersive methods in analyzing air and/or bulk material samples offers the most accurate approach to estimating airborne asbestos concentrations. 

Anomalous X-ray dispersion effects will cause intensity differences if the structure is noncentrosymmetric and contains an atom that scatters anomalously. Friedel s Law, which states that the X-ray diffraction pattern of a crystal is centrosymmetric even if the crystal structure is not, will not be obeyed. This means that, in the presence of anomalous dispersion effects, I hkl) If the structure is... 

Solid fullerene displays interesting properties. After condensation, the Cgo molecules forms a face centered cubic (f.c.c.) structure fullerite. This is the only material which consists of quasi-spherical molecules, all atoms of which are of one kind. X-ray dispersion experiments show that fullerite forms a closely packed f.c.c. crystal in which the distance between the nearest molecules is 10.04 A [2]. The least distance between two molecular surfaces is 2.9 A, and the distance between the nearest atoms in a crystal is 1.42 A. Thus, the experiments specify that the molecular structure of Ceo is preserved in the solid. Strong orientational disorder is observed at room temperature [64] and this disorder decreases as the temperatures decreases. 

The differential thermal analysis (DTA) and thermogravimetry (TG) experiments were performed on the precursors in order to follow the effect of the preparation method on the catalyst production under heating. During the experiments, samples were heated at 10°Cmin imder air flow from 30 to 1000°C, in a model Mettler Toledo TG/DTA 50. The iron contents were determined by X-ray dispersive energy in a Shimadzu EDX-700HS model equipment. The phases in the solids were identified by X-ray diffraction... 

The x-ray dispersion analysis was done on a JEOL 100C equipped with a Princeton Gamma Tech detector and Nuclear Data software. The count times were on the order of 20 min at magnifications of 20,000, 30,000, and 50,000 X. ... 

Figure lb. Phosphorus x-ray dispersion map of PNF as cast from acetone at... 

Figure 4. X-ray dispersion spectra of PNF exposed to isotonic saline, and washed. Dispersion peaks from left to right are sodium, phosphorus, and...

The x-ray dispersion analysis of the copolymers exposed to the saline solutions indicated (Figures 5 and 6) that the copolymers sequestered the sodium and chlorine ions. However, due to the low concentrations, given the limits of instrumental resolution, the location of the ions could not be mapped. 

Figure 5. X-ray dispersion spectra of the phase-mixed (chloroform-cast) copolymer (Figure 3) exposed to isotonic saline and washed. The peaks correspond to sodium, osmium, and chlorine.

The nature of the inhomogeneities of semicrystalline polymers can be expressed for spherically symmetric dispersion by means of a structure factor F(q). For X-ray dispersion, this can be represented as... 

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