Continuous X-rays

Fig. 1-3. The continuous x-ray spectrum. Note that the short-wavelength limit (Eq. 1-2) is 0.248 A for 50 kv and 0.620 A for 20 kv. A spectrum from a rectified a-c tube would have the peak displaced to the right and for a given input energy would have less x-ray output. (After Ulrey, Phys. Rev. [2], 11, 401.)...

In most ordinary cases, the disadvantages of x-ray excitation are more than compensated by the absence of the disadvantages peculiar to electron excitation, by the great convenience of Coolidge tubes (1.3), and by the absence of the large background count to which the continuous x-ray spectrum excited by electrons gives rise (1.5). 

The discussion just concluded is largely implicit in the earlier discussion of the excitation of a continuous x-ray spectrum by electron bombardment (4.1). Note that x-rays behave differently when they are used for excitation. An x-ray penetrates with little or no loss of energj" until it is absorbed, and it is the more likely to penetrate to greater depth (in regions of continuous abiorption) the greater its energy (or shorter its wavelength). 

Fig. 3. Continuous X-ray spectrum of tungsten (Z = 74) at various tube voltages...

A similar correction should be applied to the equation giving the short wave-length limit of the continuous X-ray spectrum. 

To obtain monochromatic Ka, a filter system is necessary to filter out the continuous X-rays and other characteristic X-rays, which are not generated with Ka from the X-ray tube. X-ray filters can be made from material that strongly absorbs X-rays other than Ka. Generally, materials exhibit various abilities to absorb X-rays. X-ray absorption by materials is a function of the linear absorption coefficient (fi) and mass density (p). The X-ray intensity (/) passing through an absorption layer with thickness x is expressed by the following equation. 

We should note that the primary X-ray source of XRF includes both continuous and characteristic radiation. The continuous X-rays generate the background of the spectrum. The primary... 

Figure 24.8 Single crystal structure of the monomers and a change in the lattice lengths during the continuous X-ray radiation of (a) (Z,Z)-4CI and (b) (E,E)-MDO. Polymer chains are formed along the fo-axis. Circle a-axis, triangle b-axis, square c-axis.

X-Ray Emission [1.6-1.8]. A typical X-ray emission spectrum from a W target X-ray tube at 50 kV is shown in Fig. 1.1. It consists of a continuous X-ray spectrum, or white radiation ( Bremsstrahlung ), on which are superposed a few characteristic lines (L lines), resulting fit>m the direct ionization by the impinging electrons. Table 1.3 shows the strongest characteristic lines of the extended X-ray spectrum. For more details and the O spectra, the reader is referred elsewhere [1.1]. 

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