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1. An incoming high energy photon collides with a free electron.

2. The electron recoils and takes away some of the photon’s energy.

3. The photon is scattered in a new direction with less energy.

4. Compton scattering results in the ionization of the atom and a division of the incident photon’s energy between the scattered photon and the ejected electron.

5. E o = E sc + E e- (where E o is the energy of the incident photon, E sc is the energy of the scattered photon, E e- is the kinetic energy of the scattered electron).

6. As the incoming photon energy increases, more photons are scattered forwards. Incoming photon energy ↑ => scattered photon energy ↑ + scattered electron kinetic energy ↑ + scattered electron range ↑

7. Independent of Z, increases with density. Compton scatter is important with low Z materials at high photon energies.


1. Bushberg, J. T. (2012). The essential physics of medical imaging. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. Find it at Amazon
2. Heggie, J. C., Liddell, N. A., & Maher, K. P. (1997). Applied imaging technology. Melbourne: St. Vincents Hospital.

Ⓒ A. Manickam 2018

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