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

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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
Let’s look at this graph. Notice that this is a log-log plot. The total Compton scatter coefficient is on the vertical axis, and the photon energy is on the horizontal axis. 7
Page 1 and 2: Today, we continue our talk about C
Page 3 and 4: We previously derived an equation f
Page 5: So σ 0 is the classical cross sect
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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