As discussed in Section 5.4, electromagnetic radiation with high energy (X-ray and gamma radiation) interacts with the orbital electron, the nuclear field, and the nuclei. The interactions with the orbital electrons and the nuclei are used for analyt­ical purposes.

During interactions with the orbital electrons, the intensity of X-ray or gamma radiation decreases due to the photoelectric effect and elastic and inelastic

scattering (see Figure 5.25) as determined by the general formula of radiation absorption (see Eqs. (5.3) and (5.93)).

As discussed in Section 5.4.4, the photoelectric effect produces electrons, including photoelectrons and Auger electrons, and characteristic X-ray photons. The ratio of the Auger electron emission to the characteristic X-ray photon emis­sion depends on the atomic number. For light elements, Auger electron emission has a high probability, while for heavier elements, X-ray photons are produced (see Figure 4.12).

The measurements of the energy and intensity of electron and X-ray radiation are used in different analytical techniques. The measurement of the photoelectrons gives analytical information on the chemical environment of the atoms in a substance [high-resolution beta spectroscopy and XPS]. AES (see Figure 5.24) can be used for the analysis of surface layers (Table 10.2). The characteristic X-ray photons provide information on the quality and quantity of the elements of a substance (X-ray fluorescence spectroscopy, as discussed in Section 10.2.3.1).

The elastic scattering process or X-ray diffraction (discussed in Section 10.2.3.2) is used to determine chemical structures.

The excitation of the nuclei is applied for species analysis of the compounds of the elements with isotopes that have recoil-less nuclear resonance absorption (Mossbauer spectroscopy, described in Section 10.2.2.3).