Emission spectrography

Emission reductions Emissions Emissions control Emission spectrography... 

X-ray fluorescence, mass spectroscopy, emission spectrography, and ion-conductive plasma—atomic emission spectroscopy (icp—aes) are used in specialized laboratories equipped for handling radioisotopes with these instmments. 

Sihcon has strong optical emission lines at 251.6113 and 288.1579 nm that can easily be detected by emission spectrography and that give sensitivities in the 1—100-ppm range. For nondestmctive analysis, either x-ray diffraction or x-ray fluorescence may be used (see Spectroscopy X-ray technology). 

MetaUic impurities in beryUium metal were formerly determined by d-c arc emission spectrography, foUowing dissolution of the sample in sulfuric acid and calcination to the oxide (16) and this technique is stUl used to determine less common trace elements in nuclear-grade beryUium. However, the common metallic impurities are more conveniently and accurately determined by d-c plasma emission spectrometry, foUowing dissolution of the sample in a hydrochloric—nitric—hydrofluoric acid mixture. Thermal neutron activation analysis has been used to complement d-c plasma and d-c arc emission spectrometry in the analysis of nuclear-grade beryUium. 

The detection and determination of traces of cobalt is of concern in such diverse areas as soflds, plants, fertilizers (qv), stainless and other steels for nuclear energy equipment (see Steel), high purity fissile materials (U, Th), refractory metals (Ta, Nb, Mo, and W), and semiconductors (qv). Useful techniques are spectrophotometry, polarography, emission spectrography, flame photometry, x-ray fluorescence, activation analysis, tracers, and mass spectrography, chromatography, and ion exchange (19) (see Analytical TffiTHODS Spectroscopy, optical Trace and residue analysis). 

This chapter describes the basic principles and practice of emission spectroscopy using non-flame atomisation sources. [Details on flame emission spectroscopy (FES) are to be found in Chapter 21.] The first part of this chapter (Sections 20.2-20.6) is devoted to emission spectroscopy based on electric arc and electric spark sources and is often described as emission spectrography. The final part of the chapter (Sections 20.7-20.11) deals with emission spectroscopy based on plasma sources. 

At present, the Geiger counter is the most popular x-ray detector in analytical chemistry. Although it is yielding ground to the proportional counter and the scintillation counter, it will be remembered for having greatly accelerated the use of x-ray emission spectrography in analytical chemistry. 

Figure 4-10 gives intensity distributions for crystals used in x-ray emission spectrography during 1958 in the authors laboratory. Each of the patterns shows some broadening. Only in the case of the sodium chloride crystal with the major flaw was the broadening serious enough to produce interference with the Ka lines of adjacent elements. 

For purposes of x-ray emission spectrography, the Cauchois transmitting crystal has the serious drawback of greatly attenuating the x-ray beam. It must therefore be ruled out for x-ray beams of long wavelength at all but the highest intensities, and for the determination of traces, where the intensities are low even under the best conditions. 

Before turning to Method II, we shall discuss the variation with film thickness in the intensity of a characteristic line produced in a film by x-ray excitation. The discussion that follows is significant also for x-ray emission spectrography, and the ideas are explicit or implicit in the work of Glocker and Schreiber.11... 

The modification improves performance and is interesting in connection with x-ray emission spectrography (Chapters 7, 8, and 9). It consists in measuring the intensity of tin Ka relative to that of scattered x-rays entering the detector from an analyzing crystal set for the reflection of x-rays 2.2 A in wavelength. As the tin coating becomes thicker, increased attenuation of the x-rays scattered by the iron cause s the intensity ratio to increase more rapidly than does the intensity of tin Ka. Table 6-3 contains performance data for the Quantrol on Method II (modified). The instrument can also be set up to use industrially a modification of Method III. 

H. G. J. Moseley, Phil. Mag. [6], 26, 1024 (1913). The following remarkable quotation from this paper (p. 1030) supports Moseley as the founder of x-ray emission spectrography The prevalence of lines due to impurities suggests that this may prove a powerful method of chemical analysis. Its advantage over ordinary spectroscopic methods lies in the simplicity of the spectra and the impossibility of one substance masking the radiation from another. It may even lead to the discovery of missing elements, as it will be possible to predict the position of their characteristic lines. ... 

An example of the usefulness of x-ray emission spectrography for qualitative trace analysis is shown in Figure 7-1, which contains a chart recording made in the authors laboratory of the emission spectrum from a genuine bank note. 

The analysis of thin samples by x-ray emission spectrography is based upon an extension of Equation 6-9. This equation is... 

The transition from Equation 6-9 to Equation 7-3 may be considered the simplest possible transition from determining film thickness by x-ray emission to determining film composition by x-ray emission spectrography. As the atoms in these thin samples do not influence each other as regards x-ray absorption and emission, the same experimental results may be used to support both equations. Such results are cited in Chapter 6 and below.11-14... 

The transition of the previous paragraph can be extended to include infinitely thick samples, the most common situation in x-ray emission spectrography. To determine composition, it is well to work with such... 

Equation 7-6 is thus reasonable as the basic equation for x-ray emission spectrography when only absorption effects are present. 

Sherman compares calculated and observed intensities for a number of known samples in some of which the enhancement components predominate over the intensities by direct excitation. The agreement obtained is usually within a few per cent, and this would be satisfactory even for considerably simpler problems. To be sure, the calculations do not give concentrations from measured intensities. But the fact that intensities can be satisfactorily calculated from known concentrations means that absorption and enhancement effects are thoroughly understood, and that x-ray emission spectrography is on a firm foundation. 

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