Continuous X-ray spectrum

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. 

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]. 

Besides the diseontinuous states there are also wstates forming a continuous range (with positive energy) they correspond to the hyperbolic orbits of Bohr s theory. The jumps from one hyperbola to another or to a stationary state give rise to the emission of the continuous X-ray spectrum emitted when electrons are scattered or caught by nuclei. The intensity of this spectrum has been calculated by Kramers (1923) from the standpoint of Bohr s theory by a very ingenious application of the correspondence principle. His... 

Less common detection of electrons is by photons emitted during their deceleration in a medium. The two mechanisms are creation of bremsstrahlung (continuous X-ray spectrum) and Cherenkov radiation (visible light). Cherenkov radiation is detected with a PMT bremsstrahlung X rays are detected as discussed below for gamma rays. 

For those physicists who like to study complex phenomena, the high energy photoproduction of stars and radionuclides with a continuous X-ray spectrum is probably one of the most complex situations that they can find in nuclear physics. 

For XAS a high intensity continuous X-ray spectrum is required which is most conveniently generated on a synchrotron radiation source. There are several excellent text books, at both introductory as well as advanced level, available on the theory and general application of synchrotron radia-tion and therefore we will only treat the most relevant details required for the combinations of spectroscopy and scattering techniques, which is the subject of this manuscript, here. 

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