Anodes, X-ray sources

Fig. 19. Schematic of dual anode (typically Al and Mg) x-ray source. X-rays produced by electron bombardment of anode face 2 indicated (19). The routine dual-anode x-ray source just described generates nonmonochromatized x-rays in a relatively large spot size (ca 1 cm in diameter). In...

A very narrow window produces monochromatic radiation that is still several orders of magnitude more intense than the beam from conventional rotating anode x-ray sources. Sucb beams allow crystallographers to record diffraction patterns from very small crystals of the order of 50 micrometers or smaller. In addition, the diffraction pattern extends to higher resolution and consequently more accurate structural details are obtained as described later in this chapter. The availability and use of such beams have increased enormously in recent years and have greatly facilitated the x-ray determination of protein structures. 

XPS spectra were obtained using a Perkin-Elmer Physical Electronics (PHI) 555 electron spectrometer equipped with a double pass cylindrical mirror analyzer (CMA) and 04-500 dual anode x-ray source. The x-ray source used a combination magnesium-silicon anode, with collimation by a shotgun-type collimator (1.). AES/SAM spectra and photomicrographs were obtained with a Perkin-Elmer PHI 610 Scanning Auger Microprobe, which uses a single pass CMA with coaxial lanthanum hexaboride (LaBe) electron gun. 

Application of XPS Using Silicon Anode X-Ray Source, Scanning... 

Fig. 3. Schematic drawing of the high pressure electron spectrometer. A, Argon ion gun D, differentially pumped region EL, electron lens G, gas cell HSEA, hemispherical electron analyzer LO, two-grid LEED optics LV, leak valve M, long travel rotatable manipulator P, pirani gauge S, sample TSP titanium sublimation pump W, window X, twin anode x-ray source.

The crystals of NCPs containing a-satellite DNA palindrome and chicken erythrocyte histones diffracted isotropically to 3.0 A using an in-house rotating anode X-ray source and to better than 2.5 A at a moderate intensity synchrotron beamline [30,31]. The crystals used for structure determination were grown in the microgravity environment using a counter-diffusion apparatus [32]. Ground-based... 

The Lorentzian shape of x-ray emission lines is well founded in quantum theory and has been substantiated experimentally (Hoyt, 1932). Siegbahn et al. (1967) discuss the aluminum anode x-ray source as applied to ESCA. Beatham and Orchard (1976) list doublet separations and half-widths derived from the literature and optimized by computer simulation. Kallne and Aberg (1975) and Senemaud (1968) also provide values. 

The XPS mechanism, which can be used for quantitative and qualitative chemical analysis of surfaces, is based on the photoelectric effect. A monochromatic soft Mg or Al anode X-ray source is used to irradiate the surface. The absorbed X-rays ionize die core shell, and in response, the atom creates a photoelectron that is transported to the surface and escapes. The ionization potential of a photoelectron that must be overcome to escape into vacuum is the binding energy (BE) plus the work function of the material. The emitted photoelectrons have a remaining kinetic energy (KE), which is measured by using an electron analyzer. Individual elements can be identified on the basis of their BE. The resulting XP spectrum is a characteristic set of peaks for a specific element, with BE as the abscissa and counts per unit time as... 

The low thermal efficiency of the sealed x-ray tube can be substantially improved by using a rotating anode x-ray source, which is shown in Figure... 

For more details on rotating anode x-ray sources see W.C. Phillips, X-ray sources, Methods Enzymol. 114,300 (1985) and references therein. 

Figure 3.47. The example of different quality x-ray powder diffraction data. Only thin lines connecting observed data points are shown to emphasize the difference in data quality. Both experiments were carried out using the same powdered specimen and the same powder diffractometer with rotating anode x-ray source Figure 3.13) but with different scan rates.

Reflectivity measurements on monolayers have also been carried out with neutrons. In general, x-ray sources are much more intense than neutron sources even laboratory (rotating anode) x-ray sources are two orders of magnitude more intense than neutron sources. On the other hand, the scattering-length density for neutrons of an atom is that of its nucleus and, as a result, the contrast between different parts of the interface can be altered by isotopic substitution. For hydrocarbon chains, a significant change in... 

Fig 12 is a conceptual sketch of what a CT expls detection system might look like. The objects to be examined are placed on a conveyor belt, 2 to 3 meters long, which passes between an X-ray source on one side and an array of column detectors on the other. The design speed for the conveyor is 30cm/sec. The column detectors are 60cm hi with vertical slit collimators focused on the extended-anode X-ray source. Source and detector collimation will vary depending on the distance from the source to the detector, so that the spatial dispersion of the X-ray pencil beams thru the examined olqect will be the same for ail projection angles... 

A commercial x-ray photoelectron spectrometer uses a fixed anode x-ray source, typically producing magnesium Ka or aluminium Ka radiation, which directs a beam at the sample surface. The sample chamber is held at ultra-high vacuum and the resulting photoelectrons are collected and their energy analysed in an electrostatic analyser such as a cylindrical mirror analyser. 

Fig. 2 Coordination binding of Cd + to carboxylate-terminated SAMs, (a) The number of electrons in the counterion overlayers per carboxylic acid group at the SAM surface held in 1 mM Cd + solutions at different pH values, obtained by fitting X-ray reflectivity curves. The filled circles represent measurements using synchrotron radiation the open circles were obtained using a rotating anode X-ray source. The line is a fit calculated using a modified BET multilayer adsorption model, (b) Schematic presentation of the pH-dependent equilibrium for binding of Cd + ions to a MHA SAM (adapted from Ref 28).

Hawn (1983) has described the performance of a dual-anode X-ray source for XPS using various un-collimated and collimated configurations to make it effective in increasing the signal-to-background ratio and reducing anode cross talk without substantial signal loss. 

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