Ray Spectra

To verify the modelling of the data eolleetion process, calculations of SAT 4, in the entrance window of the XRII was compared to measurements of RNR p oj in stored data as function of tube potential. The images object was a steel cylinder 5-mm) with a glass rod 1-mm) as defect. X-ray spectra were filtered with 0.6-mm copper. Tube current and exposure time were varied so that the signal beside the object. So, was kept constant for all tube potentials. Figure 8 shows measured and simulated SNR oproj, where both point out 100 kV as the tube potential that gives a maximum. Due to overestimation of the noise in calculations the maximum in the simulated values are normalised to the maximum in the measured values. Once the model was verified it was used to calculate optimal choice of filter materials and tube potentials, see figure 9. 

Whereas zirconium was discovered in 1789 and titanium in 1790, it was not until 1923 that hafnium was positively identified. The Bohr atomic theory was the basis for postulating that element 72 should be tetravalent rather than a trivalent member of the rare-earth series. Moseley s technique of identification was used by means of the x-ray spectra of several 2ircon concentrates and lines at the positions and with the relative intensities postulated by Bohr were found (1). Hafnium was named after Hafma, the Latin name for Copenhagen where the discovery was made. 

X-Rays. If an x-ray is emitted, it has an energy, AE, equal to the difference in the binding energies of the two atomic shells, E — Ej. If the original hole is in the K shell, the x-ray is called a K x-ray if the hole is in the L shell it is an L x-ray. Because the hole can be filled by an electron from any of the several outer shells, x-ray spectra contain a large number of discrete lines. 

Both the wavelength dispersive and energy dispersive spectrometers are well suited for quaUtative analysis of materials. Each element gives on the average only six emission lines. Because the characteristic x-ray spectra are so simple, the process of allocating atomic numbers to the emission lines is relatively simple and the chance of making a gross error is small. 

The X-ray determination of REE in geological samples is normally complicated by the relatively low concentrations of the REE, their complex X-ray spectra, the high concentration of matrix elements and the lack of reference standards with certified values for REE. A rapid and sensitive ion exchange and X-ray fluorescence procedure for the determination of trace quantities of rare earths is described. The REE in two U.S.G.S. standards, two inhouse synthetic mixtures and three new Japanese standards have been determined and corrections for inter-rare earth element interferences are made. 

The production of characteristic X rays is determined by the cross sections discussed above, but the observed X-ray spectra include both these characteristic peaks and a continuous background radiation. A detailed investigation of the origin of... 

The detection of impurities or surface layers (e.g., oxides) on thick specimens is a special situation. Although the X-ray production and absorption assumptions used for thin specimens apply, the X-ray spectra are complicated by the background and characteristic X rays generated in the thick specimen. Consequently, the absolute detection limits are not as good as those given above for thin specimens. However, the detection limits compare very favorably with other surface analysis techniques, and the results can be quantified easily. To date there has not been any systematic study of the detection limits for elements on surfaces however, representative studies have shown that detectable surface concentrations for carbon and... 

Fig. 4.26. Typical X-ray spectra (a) STEM bright-field image of a polycrystalline Zr02/TiC ceramic with a triple junction (b) corresponding EDX spectrum.

Fig. 4.27. Artifacts in energy-dispersive X-ray spectra. Occur renceof(a) escape and (b) sum peaks.

I9l 3 H. G. J. Moseley observed regularities in the characteristic X ray spectra of the elements he thereby discovered atomic numbers Z and provided justification for the ordina] sequence of the dements. 

Tn their years together Hahn and Meitner did significant research on beta- and gamma-ray spectra. They discovered the new element protoactinium-91 and, at Meitner s suggestion, took up, and made great progress with, work on neutron bombardment of nuclei that Enrico Fermi had commenced in Rome. In 1938, this research was suspended when Adolph Hitler annexed Austria and Meitner had to flee Germany. 

Based on the strong recommendations of her German physics colleagues, Meitner received a research position in the Stockholm laboratory of Manne Siegbahn, the Swedish physicist who had received the 1924 Nobel Prize in Physics for his precision measurements on X-ray spectra. Siegbahn provided laboratory space for Meitner, but no suitable equipment for her to continue the research she had started in Berlin, and little encouragement for her work. 

The very close similarity between the x-ray spectra of the different elements shows that these radiations originate... 

Moseley found that each K spectrum of Barkla contains two lines, Ka and K(3, and that the L spectra are more complex. Later important work, especially by Siegbahn,38 has shown that M, N, and O spectra exist and are more complex in their turn. Relatively numerous low-intensity lines are now known to exist in all series. Fortunately, the analytical chemist can afford to ignore most of these low-intensity lines in his practical applications of x-ray methods at present. It generally suffices for him to know that x-ray spectra at their most complex are enormously simpler than emission spectra involving valence electrons, and that most x-ratr lines are satisfactorily accounted for on the basis of the simple selection rules that govern electron transitions between energy states. 

The introductory treatment of x-ray spectra, characteristic (1.8) and continuous (1.5), needs expansion to make it a more useful basis for discussing x-ray optics. This expansion brings with it other benefits such as the deeper insight into the excitation of x-rays by electrons (1.4) that results from a better understanding of the intensity-wavelength relationship in the continuous spectrum. 

The first extensive1 study of x-ray excitation (1.17) as a method of producing x-ray spectra for analytical purposes was carried out by Glocker and Schreiber,17 who not only treated absorption effects very thoroughly and introduced the concept of critical thickness, but who... 

Fig. 7-11. X-ray spectra of niobium and tantalum. (Courtesy of Campbell and Carl, Anal. Chem., 28, 960.)...

Thickness gaging, of steel strip, 69-71 use of cobalt-60 for, 291 Thick-target x-ray spectra, 6, 7, 99-101 Thin films, thickness determined by characteristic line intensity, 153 Thin samples, analysis by x-ray emission spectrography, 167... 

One problem with Mendeleev s table was that some elements seemed to be out of place. For example, when argon was isolated, it did not seem to have the correct mass for its location. Its relative atomic mass of 40 is the same as that of calcium, but argon is an inert gas and calcium a reactive metal. Such anomalies led scientists to question the use of relative atomic mass as the basis for organizing the elements. When Henry Moseley examined x-ray spectra of the elements in the early twentieth century, he realized that he could infer the atomic number itself. It was soon discovered that elements fall into the uniformly repeating pattern of the periodic table if they are organized according to atomic number, rather than atomic mass. 

Pd on Carbon. The catalyst analyzed here is a commercial hydrogenation catalyst with 5% Pd supported on activated carbon (Alfa). The catalyst was ground in a mortar and pestle and dispersed dry onto a carbon coated Cu grid. While x-ray spectra from heavy metal particles down to 2nm in diameter can be obtained (O by manually directing the electron beam to the particle, digital images of Pd particles at high resolution have not been obtained previously. 

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