Gamma-rays photoelectric absorption

Gamma ray attenuation Absorption of gamma rays passing through the sediment is caused by Compton attenuation (scattering), pair production, and by photoelectric absorption. The amount of gamma ray attenuation is a measure of bulk density, from... 

Fig. 5.11. Linear absorption coefficients vs. gamma-ray energy for Si and Ge (PE = photoelectric, C =...

Gamma-ray absorption occurs as illustrated in Figure 6.16 by four different processes coherent scattering, photoelectric effect, Compton effect, and pair production. For each of these processes, a partial coefficient can be expressed ... 

Photoelectric absorption arises by interaction of the gamma-ray photon with one of the bound electrons in an atom. The electron is ejected from its shell (Figure 2.4(a)) with a kinetic energy, given by ... 

The energy level from which the electron is ejected depends upon the energy of the gamma-ray. The most likely to be ejected is a K electron. If sufficient energy is not available to eject a K electron, then L or M electrons will be ejected instead. This gives rise to the discontinuities in the photoelectric absorption curves. These... 

The probability that a photon will undergo photoelectric absorption can be expressed as a cross section, t. This measure of the degree of absorption and attenuation varies with the atomic number, Z, of the absorber and the gamma-ray energy, E fmdi complicated manner ... 

It is normally assumed that photoelectric absorption results in the complete absorption of the gamma-ray. However, for those events near to the surface of the detector there is a reasonable probability that some fluorescent X-rays, most likely the K X-rays, might escape from the detector. The net energy absorbed in the detector would then be ... 

Figure 2.4, a photoelectric absorption can be followed by the emission of a characteristic X-ray of the absorbing medium. There is a significant possibility that this fluorescent X-ray may escape the shielding and that it will be detected by the detector, as indicated in Figure 2.13. The result will be a number of X-ray peaks in the gamma spectrum in the region 70-85 keV. This may or may not be a problem in practice, depending upon the type of gamma-ray spectrum measured. However, if low-energy gamma-ray measurements are contemplated, fluorescent X-rays are an unnecessary complication.

Photoelectric absorption - total absorption of the gamma-ray energy, possibly followed by escape of fluorescent radiation (X-ray escape peaks). 

ABSORPTION EDGE The sharp changes in photoelectric absorption coefficient as a function of energy as the energy of the gamma-rays decreases, related to the energy of electrons within their shells. 

PHOTOELECTRIC ABSORPTION The process in which a photon (i.e. gamma-ray) ejects bound electrons from an atom. See also Auger electrons. 

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