X-ray intensity, measurement

Where / and 70 are the characteristic X-ray intensities measured from the unknown specimen and standard respectively, and I/IQ is commonly known as the k ratio . Co is the concentration of the element concerned in the standard. 

Figure 15 X-ray intensity measured as a function of the polar angle y for an undrawn ultra-high molecular weight PE film. Incident beam directed through the thickness of the film (A), and parallel to the plane of the film (B). Reproduced with permission from Lafrance et al. [82]. Reprinted with permission of John Wiley 8t Sons, Inc.

As early as 1829, the observation of grain boundaries was reported. But it was more than one hundred years later that the structure of dislocations in crystals was understood. Early ideas on strain-figures that move in elastic bodies date back to the turn of this century. Although the mathematical theory of dislocations in an elastic continuum was summarized by [V. Volterra (1907)], it did not really influence the theory of crystal plasticity. X-ray intensity measurements [C.G. Darwin (1914)] with single crystals indicated their mosaic structure (j.e., subgrain boundaries) formed by dislocation arrays. Prandtl, Masing, and Polanyi, and in particular [U. Dehlinger (1929)] came close to the modern concept of line imperfections, which can move in a crystal lattice and induce plastic deformation. 

In the X-X method, the same result is obtained as in the X-N procedure by making use of the fact that the high 28 X-ray intensities measured with short wavelengths, i.e., AgKa = 0.560 A, are determined only by the inner core, Is, electrons for first row elements. This method has the obvious advantage that all measurements are made on the same crystal. The tuneable wavelength property of synchrotron X-rays is useful for this type of experiment. 

Electromagnetic radiation, such as a bea m of x-rays, carries energy, and the rate of flow of this energy through unit ansa perpendicular to the direction of motion of the wave is called the intensity /. proportional to the square of the amplitude In absolute units intensity is measured in joules/m /sec, but this measurement is a difficult one and is seldom carried out most x ray intensity measurements are made on a relative basis in arbitrary units, sudi as the degree of blackening of a photographic film exposed to the x-ray beam. 

ABRAHAMS asked for comments on the Tukey-Schomaker proposal to measure overlapping data blocks, or measure each reflection at least twice, so that one can extrapolate back to zero exposure and thus correct for the effects of radiation damage on the x-ray intensity measurement. SCHOMAKER replied as follows ... 

Similarly to Pt/Rh alloying, modifications of step 1 duration show that cerium aluminate is formed only when reducing conditions are present in the cycle, most probably to ensure reduction of Ce4+ (Ce02) to Ce + (CeAlOs). Moreover, as deduced firom X-ray intensities measurements, the CeA103/Ce02 ratio increases with duration of the reducing step (for these experiments, the number of cycles was kept constant to 50 in four hours by modifying neutral phases durations, steps 2 and 4). 

Fig. 1.4 The X-ray intensity measured at three reciprocal lattice positions (indicated in Fig. 1.3) as the potential was cycled over the range 0.05-1.15 V vs RHE (sweep rate = 2 mV s ). At each position the intensities are normalized to the intensity measured at 0.05 V. The vertical line marker denotes the two potential regions of interest (see text taken from Ref [34]).

X-ray intensity measurements for all possible reflections with sin 0/X < 0.64 were made by 6-0) scan on a Nonius CAD4 diffractometer. 

X-ray intensity measured in coulomb per unit mass (C/kg) Local collocation point index in z-coordinate 7-ray intensity measured in coulomb per unit mass (C/kg) Spectral radiation intensity of blackbody emission (W /m sr xm)... 

The oxygen atoms in rhombohedral PbO have proved impossible to locate by X-ray intensity measurements, but their positions were determined by neutron diffraction. The structure consists of a chain in which lead has two nearest oxygen neighbours (Pb-0 = 2 21 A). These chains are loosely bonded into layers by two Pb-O bonds (Pb-0 = 2 49 A). 

The replacement of film by automatic counter methods provides a potential increase in speed and accuracy. The American Crystallographic Association recently sponsored a project to obtain a quantitative comparison of the absolute accuracy and assess the various systematic errors involved in X-ray intensity measurement. Seven well-known crystallographers measured intensities from the same crystal, a small CaF2 sphere, using all major types of counter... 

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