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

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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. 2
We previously derived an equation for the differential scatter cross section per unit solid angle. The first step toward obtaining the total scatter cross section is to convert the differential scatter cross section per unit solid angle to the differential scatter cross section per unit plane angle. We are going to do the exact same thing that we did with coherent scatter and use the relationship dΩ = 2π sin θ dθ. So dσ/dθ is equal to dσ/dΩ times dΩ/dθ, which is dσ/dΩ times 2π sin θ. This is exactly what we did before with the cross section for coherent scatter. 3
Page 1: Today, we continue our talk about C
Page 5 and 6: So σ 0 is the classical cross sect
Page 7 and 8: Let’s look at this graph. Notice
Page 9 and 10: What about the dependence of the Co
Page 11 and 12: The energy transferred to the elect
Page 13 and 14: If we plot the energy transfer coef
Page 15 and 16: The energy transfer coefficient has
Page 17 and 18: What about the scatter coefficient?
Page 19 and 20: Using this equation we can now plot
Page 21 and 22: This probability is represented by
Page 23 and 24: This figure is a plot taken from Jo
Page 25 and 26: We can always calculate what the ma
Page 27 and 28: Remember dσ/dE is relatively const
Page 29 and 30: Now we also look at the graph and s
Page 31 and 32: First, let’s recall that the atte
Page 33 and 34: What we now want to find out is how
Page 35 and 36: So far, our approximations have bee
Page 37 and 38: These values were tabulated by Hubb
Page 39 and 40: So what is the effect of binding en
Page 41 and 42: At higher energies there is no diff
Page 43 and 44: Note that this graph is for very lo
Page 45: The fraction of energy transferred

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

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