X-ray peaks

In rare cases from light-element X-ray peak shifts... 

X-Ray Fluorescence (XRF) is a nondestructive method used for elemental analysis of materials. An X-ray source is used to irradiate the specimen and to cause the elements in the specimen to emit (or fluoresce) their characteristic X rays. A detector s)rstem is used to measure the positions of the fluorescent X-ray peaks for qualitative identiflcation of the elements present, and to measure the intensities of the peaks for quantitative determination of the composition. All elements but low-Z elements—H, He, and Li—can be routinely analyzed by XRF. 

The height of a given X-ray peak is a measure of the amount of the corresponding element in the sample. The X-ray production cross-sections are known with good accuracy, the beam current can be measured by, for example, a Faraday cup (Figure 4.1) and the parameters of the experimental set-up are easily determined so that the sample composition can be determined in absolute terms. 

The advantage of p-PIXE analysis over the scanning electron microprobe arises from the presence of a strong Bremsstrahlung background in the latter, which tends to mask the characteristic X-ray peaks. There is thus a striking difference in sensitivity between the two techniques the detection limits are of the order of 0.1% for the electron microprobe and 0.001% for p-PIXE. 

Energy-dispersive X-ray analyses were carried out by using the ratio technique (equation 1) to relate compositions to the intensities of the CoKa and WL characteristic X-ray peaks. The value of the kw Co factor was experimentally determined using single-phase eCo samples. A series of EDX analyses was performed from the edge to the interior of the foil and the results plotted in the form of the relationship ... 

Figure 5.24(B) shows a line profile extracted from the map of Figure 5.24(A) by averaging over 30 pixels parallel to the boundary direction corresponding to an actual distance of about 20 nm. The analytical resolution was 4 nm, and the error bars (95% confidence) were calculated from the total Cu X-ray peak intensities (after background subtraction) associated with each data point in the profile (the error associated with A1 counting statistics was assumed to be negligible). It is clear that these mapping parameters are not suitable for measurement of large numbers of boundaries, since typically only one boundary can be included in the field of view.

Quantitative concentration data are often required from XRF analyses. In principle (for both WD and ED) the intensity of the fluorescent X-ray peak is proportional to the amount of the element present. This is complicated, however, by absorption and enhancement processes. Absorption can cause both attenuation of the input (primary) radiation and the fluorescent (secondary) radiation, as discussed above. Enhancement is the result of the observed element absorbing secondary radiation from other elements present in the sample, thus giving more fluorescent radiation than would otherwise... 

Once we have the appropriate nuclide, we must separate the radiation of interest from all other radiation present. A typical gamma spectrum is shown in Figure 3 for cobalt-57 in palladium. The radiations which can be identified include the 6-k.e.v. x-ray, the 14-k.e.v. y-ray of interest, and a sum peak and palladium x-ray peak, both lying at about 21 k.e.v. If one now sets the single-channel analyzer window correctly, one observes essentially only the 14-k.e.v. peak, but all of this is not recoil-free radiation it includes other radiation which falls into the window from various gamma quantum de-excitation processes. 

X-Ray Diffraction (XRD) is well known technique based on scattering of X-rays. It can be applied to semiciystalline or crystaline polymers and structural changes induced by modification. Occasionally observed shifts in the X-ray peak positions might indicate a distortion of the crystal structure due to increasing strain. The width of the X-ray reflection peaks yields information on the size of the crystals rmder investigation. 

Crystallization was followed by analyzing the solid product quantitatively by x-ray powder diffraction. Prepared mixtures of a standard sample of mordenite and the amorphous substrate of mordenite composition were used to establish a calibration curve for the quantity of mordenite based on the summation of x-ray peak intensities. For zeolites A and X, the unreacted aluminosilicate gel was used to prepare mixtures with standard samples of zeolites A and X for quantitative phase identification. 

The crystal size in polyphenylene, as determined from x-ray peak widths, is of the order of 5 nm476) with a disorder parameter g = 0.026 nm. Compression at up to 12kB decreased the (/-spacing perpendicular to the chains, decreased the peak size and increased the disorder slightly. Annealing at temperatures above 250 °C increases the crystal size and perfection 472). The spin concentration increases above 300 °C, but unlike those in polyacetylene, these spins are not mobile477. The crystallinity has variously been estimated as 80% 327) and 20 to 30% 478). It seems to depend on the catalyst used in the Kovacic method. Polyphenylene produced by the precursor route has a crystallinity from 60-80% dependent on the conversion conditions 252). 

Fig. 7 Correction factors for the x-ray peak at 32 keV (a) and the correction factors for the 662 keV peak (b) as functions of the total count rate measured on a low-energy p-type detector with a 60Co source...

There was no microparticle evidence of increased oil-combustion emissions in the high-[SO -] air mass. Oil fly ash is generally platy or honeycombed carbon which is enriched in V and Ni (19.22,30). Two particles yielded very small V x-ray peaks but these peaks were not associated with a specific particle type or elemental combination. 

---