|Message: Puzzle bout effective atomic number||Not Logged In (login)|
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I am trying to use effective atomic numbers (effective Z) to calculate the absorbed dose of 35keV X-ray by biological tissues. To verify the correctness of the usage of this parameter. I built two boxes next to each other, one made of actual water, and the other made of effective water using Z = 7.42, A = 18 g/mol, and density = 1.0 g/cm3. An X-ray irradiates the two boxes in parallel. The strange thing is: the absorbed dose by the effective water is only about half that by the actual water with the standard EM physics. And with Livermore, D_eff : D_water is about 0.6.
When the energy is changed to 85keV, the ratio is about 0.55 with standard EM physics and 0.75 with Livermore.
If Z is 7.62 instead of 7.42, then with standard EM and photon energy of 85 keV, the ratio is about 0.6, and with Livermore and at the same energy, the ratio is about 1.0.
I am left with two questions: how should I choose a proper way to calculate the effective Z and how should I choose the model of physics at a given energy, say 28 keV?
I do know that effective Z may be calculated with different parameters at different energies and different range of Z, and effective Z may not be a good parameter when the energy is lower than 30 keV. But I just know a little. Is there any paper discussing this issue?
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