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

Take a look at that table, and observe the energy dependence of the Compton scatter
coefficient for free electrons. Remember we said that the classical cross section was
independent of energy. Now let’s look at the correction due to multiplying the
classical attenuation coefficient by the integral of the Klein-Nishina coefficient.
At 1 keV the Compton cross section is roughly equal to the classical value – it’s
roughly 10 -28 m 2 /electron.
At 7 MeV, we are down 1 order of magnitude; at 100 MeV we are down two orders
of magnitude.
Now notice this. From 1 keV to 100 MeV, the scatter coefficient drops down two
orders d of f magnitude. it d As A a function f ti of fenergy we go down d five fi orders d of f magnitude it d
of energy from 1 keV to 100 MeV, but we only drop down two orders of magnitude
in the Compton scatter coefficient. Because of this we say the Compton scatter
coefficient is roughly independent of energy.
6