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

Let us first review what we’ve covered so far about Compton scatter cross sections.
We’ve said that the Compton scatter cross section is equal to the classical scatter
cross section in the limit of zero energy. It’s also equal to the classical scatter cross
section for forward scatter, that is, θ = 0. The Compton scatter cross section
becomes more peaked in the forward direction as the photon energy increases. The
Compton scatter cross section for backscattered photons, that is, θ = π, is lower than
that for θ = 0 by about one order of magnitude for photons of energy 1 MeV, and
about two orders of magnitude for photons of energy 10 MeV. This is what we
know so far about Compton scatter.
What we are going to do now is try to get an equation, first of all for the total scatter
cross section, and then we will look at the energy gy dependence p of the cross section.
The total scatter cross section is the attenuation coefficient per unit incident photon
fluence. Thus, from the scatter cross section we will be able to obtain the
attenuation coefficient.
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