Bremsstrahlung radiation

A typical x-ray photoelectron spectmm consists of a plot of the iatensity of photoelectrons as a function of electron E or Ej A sample is shown ia Figure 8 for Ag (21). In this spectmm, discrete photoelectron responses from the cote and valence electron energy levels of the Ag atoms ate observed. These electrons ate superimposed on a significant background from the Bremsstrahlung radiation inherent ia n onm on ochrom a tic x-ray sources (see below) which produces an increa sing number of photoelectrons as decreases. Also observed ia the spectmm ate lines due to x-ray excited Auger electrons. 

The detector itself may be shielded from background y-rays by means of an annular shield of W or Pb, and absorbers in the form of appropriate metal foils are placed between the detector and the specimen. These reduce the intensity of the continuum of Bremsstrahlung radiation and also prevent back-scattered protons from entering the detector which would degrade the observed spectrum. 

In inverse photoemission spectroscopy or Bremsstrahlimg Isochromat Spectroscopy, the sample is bombarded with monoenergetic electrons and the Bremsstrahlung radiation is recorded at constant photon energy for varying kinetic energy of the incident electrons. The electronic process involved is just the inversion of the photoemission process, and therefore, instead of investigating occupied states as in UPS/XPS, empty states are examined in BIS. 

In the strictest sense, the term gamma ray is applicable only to photons produced as a result of transitions in atomic nuclei. However, the term is also sometimes used to denote bremsstrahlung radiation produced when the high energy electrons in the beam of an electron accelerator, such as an electrostatic generator, a betatron, a synchrotron, or a linear accelerator, strike the target of that accelerator. 

FIGURE 5.4 An x-ray spectrum from a normal skin sample obtained by PIXE-analysis. Detectable peaks are seen above the continuous background (Bremsstrahlung) radiation. Note that the Na peak is not detectable (due to absorption in the sample and the detector window). 

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