Characteristic emission lines

Both WDXRF and EDXRF lend themselves admirably to quantitative analysis, since there is a relationship between the wavelength or energy of a characteristic X-ray photon and the atomic number of the element from which the characteristic emission line occurs. The fluorescence intensity of a given element is proportional to the weight fraction. Emitted fluorescence radiation is partly absorbed by the matrix, depending on the total mass absorption coefficient ... 

The interaction of an electron with an atom gives rise to two types of X-rays characteristic emission lines and bremsstrahlung. The atom emits element-characteristic X-rays when the incident electron ejects a bound electron from an atomic orbital. The core-ionized atom is highly unstable and has two possibilities for decay X-ray fluorescence and Auger decay. The first is the basis for electron microprobe analysis, and the second is the basis of Auger electron spectroscopy, discussed in Chapter 3. 

The quantitative analysis of thick specimens, as carried out in the electron microprobe, is well documented (15). The concentration, cx, of the element x present in a specimen is related to the intensity, Ix, of a characteristic emission line of x by the equation... 

The use of graphite electrodes is responsible for the observed characteristic emission lines of radicals and organic functional groups (e.g. cyanogen CN bands between 320 and 400 nm) and also for the background continuum they generate. 

Once the characteristic emission line has been isolated by the spectrometer, the detector and its related electronic system are used to measure the intensity of the emission line. The detector is a photoelectron multiplier. Photoelectron multipliers can be used to measure light over an extensive range of wavelengths. They can amplily very low emission levels and their response range can be extended to more than nine orders of magnitude in luminous intensity. 

Figure 1-11 shows clearly how the wavelengths of characteristic emission lines can be calculated, since the difference in energy between two states will equal h, where v is the frequency of the radiation emitted when the atom goes from one state to the other. Consider the Ka.i characteristic line, for example. The L level of an atom is actually a group of three closely spaced levels (Lj, Ln, and L, ), and the emission of the Kot line is due to a AT -> L, transition. The frequency of this line is therefore given by the equations... 

Wavelengths (in A units) and Energies (in keV) of Some Characteristic Emission Lines and Absorption Edges... 

The characteristic emission of X-rays from an X-ray tube, in the strict sense, is not monochromatic (Figure 6.2). The energy distribution of a single characteristic emission line can be described by the Lorentz function ... 

Class III objects are weak line T Tauri stars (T Tauri stars in which the characteristic emission lines are only weakly observed in their optical spectra) and have little or no evidence of a disk. At this stage of solar nebula evolution, which may last between 3 and 30 Ma, the sun has formed, and the material of the nebula is being dissipated by solar winds in the inner part. In the outer part of the nebula material is dissipated by photo-evaporation caused by UV radiation from the solar wind. A positive pressure gradient near the inner edge of the nebula facilitates planetesimal formation. 

The Rotary Disk Electrode (RDE) - ASTM D6595 The RDE instrument has this name because the sample fluid is transported into a high temperature arc by means of a rotary carbon disc. The disc is immersed into the sample vessel, usually the bottle cover, and picks up oil and wear metals as it turns. The arc raises the energy states of the metal atoms in the oil causing them to emit their characteristic emission lines. 

Table A2.1. The wavelengths of the characteristic emission lines of various anode elements used in X-ray generators (in A).

Because the noble gases are odorless, colorless and generally unreactive, many of the common analytical tests used for identifying elements are not useful. However, the noble gases do emit light of certain colors when exposed to an electric current and have characteristic emission line spectra. 

Table 8.3 Wavelengths of Absorption Edges and Characteristic Emission Lines of Various Elements...

Further typical of survey spectra are the strong features of step functions in the background which are proportional in their height to the integrated intensity of the characteristic emission lines. These step functions arise from the inelas-... 

There are always four stages in any scheme of x-ray emission analysis. The excitation of characteristic radiation from the specimen by bombardment with high-energy photons, electrons, protons, etc. the selection of a characteristic emission line from the element in question by means of a wavelength or energy-dispersive spectrometer the detection and integration of the characteristic photons to give a measure of characteristic emission line intensity and finally, the conversion of the characteristic emission line intensity to elemental concentration by use of a suitable calibration procedure. 

Figure 8.3 X-ray emission spectrum obtained by bombarding (a) rhodium metal (Rh) and (b) silver metal (Ag) with eiectrons. Both a broad continuum (Bremsstrahiung) and sharp characteristic emission lines from the metal are seen, (a Thermo Fisher Scientific, www.thermofisher.com. Used with permission b Amptek Mini-X silver (Ag) XRF tube output spectrum Courtesy of Amptek, Inc., Bedford, MA, www.amptek.com.)...

During the last years of the nineteenth century it was found that the light that emerges through a hole from the hollow center of a hot body does not show characteristic emission lines, but has a smooth distribution of intensity with wavelength, characteristic of the temperature but independent of the nature of the hot body. The theoretical physicists who were... 

Plasma sources produce spectra rich in characteristic emission lines, which makes them useful for both qual-... 

Figure 21-17 illustrates the use of the electron microprobe for the analysis of an -cohenite (Fe,C) particle in a lunar rock. The data were obtained by a linear scan of the particle observed visually on the surface and by measurement of the intensity of the characteristic emission line for each of four elements. 

Breakdown spectra of this sample do not reveal characteristic emission lines of Cr. It may be explained by the extreme sensitivity of laser-induced luminescence for the elements with allowed luminescence electronic transitions. 

In compounds of tripositive Ln, intra 4f electronic transitions characterize optical spectra. Narrowbands and long-lived excited states (microseconds to milliseconds) are the main intrinsic characteristics. Emission lines spanning the electromagnetic spectrum from the UV to the IR allow apphcations in several different domains. The richness of the SGM and the hybrid strategy are well employed in the preparation of new multifunctional lanthanide containing composite materials. Some reviews have been published and are indicated for general information [22-28]. 

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