- #1
taffer33
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Concrete for example - you need less concrete to obtain the same lead equivalent for photon energy 500 keV than for 200 keV. What is the reason for this?
A Why does the effectiveness of low-Z shielding increase with photon energy?
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The effectiveness of low-Z shielding, such as concrete, increases with photon energy due to the predominance of the Compton effect in higher energy interactions, which is independent of atomic number. At 500 keV, less concrete is required to achieve the same lead equivalent compared to 200 keV, as the mass attenuation coefficient decreases with increasing gamma energy. Although the mass energy-absorption coefficient shows a slight increase between 0.2 to 0.5 MeV, this is misleading because higher energy photons scatter to lower energies, enhancing overall shielding effectiveness. The elemental properties of lead, particularly its absorption edge at around 88 keV, play a significant role in this dynamic. Understanding these interactions is crucial for effective shielding design in applications like PET departments.
- #2
taffer33
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Ok, I did some thinking ;) Is it because for low Z materials, photons with higher energy interacts with absorber almost by Compton Effect only? And Compton is independant of atomic number.
- #3
Astronuc
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Can one show some calculations or data to support the assertion that "you need less concrete to obtain the same lead equivalent for photon energy 500 keV than for 200 keV." The mass attenuation coefficient continually decreases as a function of gamma energy, although the mass energy-absorption coefficient increases slightly between 0.2 to 0.5 MeV. But this is misleading, since the 500 keV gamma will scatter to a lower energy, and that photon will scatter, and so on.
https://physics.nist.gov/PhysRefData/XrayMassCoef/ComTab/concrete.html
https://physics.nist.gov/PhysRefData/XrayMassCoef/ComTab/concrete.html
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- #4
taffer33
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https://archive.org/details/jresv38n6p665
it's in this article for example
I asked this question as I was reading about shieldings in PET departments, where they suggest lead/concrete ratio 12-15, while ratio for 150 keV X-Ray is 80... (These are example regulations from my country).
it's in this article for example
I asked this question as I was reading about shieldings in PET departments, where they suggest lead/concrete ratio 12-15, while ratio for 150 keV X-Ray is 80... (These are example regulations from my country).
- #5
Vagn
- 520
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It's a property of lead rather than a property of the concrete.taffer33 said:
Have a look at the cross-section per unit mass of lead below, and compare it to the same for concrete:
Lead has an elemental absorption edge at around 88keV, so the cross-section for lead is massively increased when the photon energy, as the photon energy is further increased, the photo-ionisation cross-section due to that particular energy-level decreases, becoming more comparable to that of the concrete.
My question is about the following graph:
I keep on reading that fusing atoms up until Fe-56 doesn’t cost energy and only releases binding energy. However, I understood that fusing atoms also require energy to overcome the positive charges of the protons. Where does that energy go after fusion? Does it go into the mass of the newly fused atom, escape as heat or is the released binding energy shown in the graph actually the net energy after subtracting the required fusion energy?
I...
Hello everyone,
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Any help would be appreciated.
J.
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