Up until this point, the photon only has has enough energy to ionize electrons. However, when the photon energy exceeds the nuclear binding energy (on average about 8 MeV per nucleon), its energy can be absorbed by a proton or neutron, which escapes the nucleus and ionizes the atom. The probability of photonuclear interactions is very low compared to the main three and is not considered in this discussion, but in some cases the interaction produces noticable effects. For example, the photonuclear interaction creates neutrons in linear accelerators, which must be accounted for in radiation shielding.
References and Further Reading
- Introduction to Radiological Physics and Radiation Dosimetry. Chapter 7
- AAPM Summer School 2009. Chapter 2
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