Photons Compton scattering

Photons, Compton-scattered, 21 312 Photon spectrum, 21 296 Photon stimulated desorption (PSD), 24 74 Photooxidation, 9 385-386 dye-induced, 19 195 in industry, 9 518 reactions, 9 515-518 Photooxidative degradation... 

The photoelectric interaction is the most probable process up to a few hundred keV and that is the only interaction that results in a complete absorption of the photon. Compton scattering may occur at all energies, but is the most important between a few hundred keV and a few MeV, while at high energies pair production becomes the most important interaction (see e Fig. 31.4). 

Matscheko and Ribberfors, A Compton scattering spectrometer for determining X-ray photon energy spectra. Phys. Med. Biol., 1987. 32(5) p. 577-594. 

Fig. 6. Schematic illustration of the relationships of the original y-ray and the scattered radiations for Compton scattering where E is the energy of the incident photon, E is the energy of the recoiling electron, and E is the energy of the scattered photon.

In addition to Compton scattering, y-rays having energies above 1022 keV interact with matter by a process called pair production, in which the photon is converted into a positron and an electron. The y-ray energy in excess of the 1022 keV needed to create the pair is shared between the two new particles as kinetic energy. Each j3 -particle is then slowed down and annihilated by an electron producing two 511-keV photons. 

For 7-ray energies below 1 MeV (the range of interest) there are two principal modes of interaction with matter — Compton scattering and photoelectron absorption. Compton scattering is the elastic scattering of the 7 photon by an orbital electron in which part of the incident 7-energy is imparted to the recoiling electron. 

The Compton effect, in which the photon is scattered with significantly lower energy by a medium electron, which is then ejected with the energy differential. 

X-ray attenuation occurs via four basic modes of interaction, shown schematically in Figure 4. Coherent X-ray scatter (CXRS) is an energy preserving interaction between an X-ray photon and an entire atom or crystalline matrix. Incoherent or Compton scatter represents a direct interaction between an X-ray and an... 

Figure 5 X-ray mass attenuation coefficients for aluminum as a function of photon energy. At low energies, photoelectric absorption predominates. At higher energy, incoherent (Compton) scatter becomes almost the exclusive contributing mode. Eventually, pair production dominates at very high energies (above 10 MeV).

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