BRAINCAKEPhotoelectric Effect, Compton Scattering and Pair Production
Three of the attenuation mechanisms change or destroy the X-ray photon.
Photoelectric effect (below about 100 keV): the photon is completely absorbed by an inner electron of an atom, and that electron is ejected. The photon disappears. The chance of this rises steeply with proton number, so bone (containing calcium) absorbs much more strongly than soft tissue. This is the main mechanism that makes X-ray images.
Compton effect (about 0.5 to 5 MeV): the photon interacts with an outer electron. The electron is ejected and the photon is scattered with less energy, so it has a longer wavelength and travels in a new direction. Energy and momentum are shared between the electron and the scattered photon.
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More in Medical Imaging
- Production of X-rays
- X-ray Tubes
- X-ray Attenuation Mechanisms
- Attenuation of X-rays
- Contrast Media
- CAT Scanning
- Medical Tracers
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All 20 lessons in Medical Imaging · All OCR A-level Physics topics