Processes and X-Ray Production

Inner-shell ionization by electrons is the oldest experimental process of characteristic X-ray production. 

The literature often refers to X-ray yields, that is to the number of selected characteristic photons produced per steradian per incident electron as a function of the energy of the electron beam bombarding the target made of atoms Z. It is not straightforward to go from 

Classical theories of atomic collisions were developed on the basis of binary collisions and for Coulomb collisions, providing approximate inner-shell cross sections of any atom [2]. Quantum mechanics contributed to calculations of the angular differential cross sections and total cross sections under various approximations. A fundamental step is due to Bethe [3]. 

A review of quantum theories (Born approximation, Bethe approximation, impulse approximation, etc.) as well as information on the classical calculations can be found in [4] (up to 1968) see also [5]. 

Using the generalized oscillator strength formulation of the Born approximation, McGuire [6] calculated total electron-ionization cross sections, for elements with 19 2 54. A compilation of experimental data was published in [7]. Experimental values of may include multiple ionization contribution. 

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Attenuation by scattering or pair-production processes is not treated at all in the present Volume. Attenuation by ionization of inner shells is treated in the Section on Ionization Processes and X-Ray Production , pp. 217/20. Compilations of individual and total photon cross sections (attenuation coefficients) for the whole range of photon energies were cited in, e.g., Tungsten Suppl. Vol. A2, 1987, pp. 69/77. 

In the process of X-ray production by electron bombardment however, the electron energy (product of electron charge e and accelerating potential V) must be greater than the binding energy of the shell (i.e., E for K X-rays). 

Fig. 1. The process of X-Ray production in EDX measurements of samples (a) showing how an inner orbital electron is ejected out from an electron coming from the electron gun of a SEM/TEM and (b) the production of characteristic X-Rays from the transition of an outer electron orbital to the inner orbital...

The nickel oxide modification obtained electrochemicaHy in KOH electrolyte contained potassium ion and its nickel oxidation level are higher than that of NiO 5. Conclusions regarding the transitions between the reduced and oxidized products within the two series are that the redox process was not reversible and although the oxidized phases of the P- and the y-nickel hydroxides differ in energy contents, differences in analyses and x-ray patterns are not significant. 

The characteristic feature of solid—solid reactions which controls, to some extent, the methods which can be applied to the investigation of their kinetics, is that the continuation of product formation requires the transportation of one or both reactants to a zone of interaction, perhaps through a coherent barrier layer of the product phase or as a monomolec-ular layer across surfaces. Since diffusion at phase boundaries may occur at temperatures appreciably below those required for bulk diffusion, the initial step in product formation may be rapidly completed on the attainment of reaction temperature. In such systems, there is no initial delay during nucleation and the initial processes, perhaps involving monomolec-ular films, are not readily identified. The subsequent growth of the product phase, the main reaction, is thereafter controlled by the diffusion of one or more species through the barrier layer. Microscopic observation is of little value where the phases present cannot be unambiguously identified and X-ray diffraction techniques are more fruitful. More recently, the considerable potential of electron microprobe analyses has been developed and exploited. 

Hydrobromide. A complex process takes place in the first step of weight loss of melamine hydrobromide (250-400 C) as shown by the DTG curve of Figure 6. The products evolved in this step were shown to be a mixture of melamine hydrobromide (IR) and ammonium bromide (IR and X-ray). The IR spectrum of the residue (55% at 400 0 which is compared with the original salt in Figure 7, is identical with that of reference melam hydrobromide. Furthermore, the IR of the residue... 

In this work, we will show that the addition of TCM to the feedstream in the methane conversion process results in the enhancement of the conversion of methane and the selectivity to C2 hydrocarbons on praseodymium oxide primarily as a result of the formation of praseodymium oxychloride, in contrast with the production of carbon oxides on praseodymium oxide in the absence of TCM (8-10). The surface properties of these catalysts are characterized by application of adsorption experiments and X-ray photoelectron spectroscopy (XPS). 

II) Mass Flow Binaries that are the products of internal evolutionary processes also include Novae and X-ray binaries that are thought to contain compact objects. Also, there is strong evidence that many, if not all, symbiotic stars are binaries. 

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