X-ray tube spectrum

The greatest disadvantage of the scheme is the difficulty it causes in obtaining broadband excitation. Even if the x-ray tube can be mechanically moved to irradiate the specimen directly, its output is too intense to be used in direct excitation. Most high-power tubes are unable to operate stably in the microampere (/xA) current range that is required for direct excitation with energy-dispersive spectrometers mounted close to the specimen. The alternative is to replace the secondary fluorescer with an efficient scatterer such as carbon or some form of hydrocarbon. This scatters the x-ray tube spectrum onto the specimen. Unfortu-... 

In the application of the fundamental parameters technique, algorithms of the general form given in Table 2.2 are employed. The usual procedure involves the prior measurement of the x-ray tube spectrum and replacement of the integral in the basic equation by an expression of the form... 

Characteristic lines in the x-ray tube spectrum scattered by the specimen (anode lines and contaminant lines)... 

Since both coherent and incoherent scattering are involved, there is broadening of the characteristic lines, depending on the line energies and the spectrometer resolution. Frequently the X-ray tube spectrum contains imwanted characteristic lines from materials used in the anode and window construction. These lines become interfering peaks as they scatter from the specimen just like the major characteristic anode lines. 

Rontgen-priifung, /. X-ray testing or examination. -rfihre, /. Rontgen tube. X-ray tube, -spektralanalyse, /. X-ray spectrum analysis, -spektrum, n. X-ray spectrum, -strahlen, m.pl. Rontgen rays, X rays. 

When the target of an x-ray tube is struck by electrons, these are retarded by the atoms of the target. The energy the electrons lose is radiated in a spectrum that ranges from the x-ray region into the infrared ye say this spectrum has been produced by electron excitation. 

Fig. 1-15. The molybdenum spectrum excited by 35-kv electrons and by the polychromatic beam from a 35-kv x-ray tube. With x-ray excitation, most of the energy appears in the characteristic lines. With electron excitation, most of it is wasted in the continuous spectrum.

Fig. 4-3. Lines from copper, nickel, and iron impurities which appeared in the spectrum of an x-ray tube after the tube had been operated for several hundred hpurs. X-rays from the tube were scattered by filter paper in the sample holder.

For many of the analytical techniques discussed below, it is necessary to have a source of X-rays. There are three ways in which X-rays can be produced in an X-ray tube, by using a radioactive source, or by the use of synchrotron radiation (see Section 12.6). Radioactive sources consist of a radioactive element or compound which spontaneously produces X-rays of fixed energy, depending on the decay process characteristic of the radioactive material (see Section 10.3). Nuclear processes such as electron capture can result in X-ray (or y ray) emission. Thus many radioactive isotopes produce electromagnetic radiation in the X-ray region of the spectrum, for example 3He, 241Am, and 57Co. These sources tend to produce pure X-ray spectra (without the continuous radiation), but are of low intensity. They can be used as a source in portable X-ray devices, but can be hazardous to handle because they cannot be switched off. In contrast, synchrotron radiation provides an... 

Figure 5.4 X-ray tube output spectrum, showing continuous emission and line spectra of the target material (in this case gold). The K absorption edges for major elements in silicate glasses are shown below the diagram, indicating that the gold M lines are particularly effective for the analysis of the light elements Na to P.

Figure 2.19 A detailed plot of the spectrum from a Cu X-ray tube, in the vicinity of the K lines, showing the area selected by the high resolution and high intensity settings of the beam conditioner shown in Figure 2,20...

Figure 2 Typical spectrum from an X-ray tube with a tungsten anode operated at 150 kVp. Fluorescence peaks occur at 57.98, 59.32,67.24, and 69.08 keV.

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