The photon can deposit energy in the tumor through the photoelectric effect and Compton effect.
The photoelectric effect dominates at a low energy X-rays while the Compton effects at high energy.
In Photoelectric all the photon energy is transferred to eject an electron from the atom, while in Compton effect the x-ray photon gets deflected and loses its energy to the electron.
Comparing the photoelectric effect and Compton effect:
The PE effect is one of the prominent ways of interaction of x-ray with matter.
In this process, a low energy photon interacts with the electron in the atom and eject it from its shell.
The incident photon is completely absorbed in this process, and the ejected electron is called as photoelectron.
The PE effect helps the x-ray beam to pass it through the matter.
Photoelectric effect or photoelectric absorption depends on the atomic number Z, the energy of the incident of the photon E and medium-density p,
Hence, if we double the atomic number Z the PE absorption will increase by a factor of 8.
This is the major contributor to the beam attenuation up to 30 Kev.
This is also a principle form of photon interaction
This process occurred when a photon interacts with an electron. After interaction, the photon is scattered and imparts its energy to the recoil electron.
This is a partial absorption process, in this process, the initial photon has lost some energy.
The Compton effect is inversely proportional to the photon energy.
Unlike other processes ( PE effect) it does not depend on the atomic number.
Thus the Compton effect is independent of the atomic number z.
It is the dominant process when human tissues are irradiated in the 30 Kev to 30 MeV energy range, which is known as the diagnostic radiation range.
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