link to lecture transcript - UT-H GSBS Medical Physics Class Site

The fraction of energy transferred to kinetic energy of charged particles per
collision increases with increasing photon energy. For low energy photons, energy
transfer is low, σ tr is much smaller than σ; Compton scatter is not an efficient means
of energy transfer. For high energy photons, σ tr is approximately equal to σ, and
Compton scatter is an efficient method of energy transfer. And finally, in soft tissue
Compton scatter is the most important process in the energy range of 30 KeV to 30
MeV.
We’ve spent a lot of time on Compton scatter. The reason we’re spending a lot of
time on it is because Compton scatter is a very important process. It’s the most
important process in the therapy energy range and matches the photoelectric effect
for importance in the diagnostic energy range.
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