Which property best describes the tissue in which the photoelectric effect occurs according to the animation?

Which property best describes the tissue in which the photoelectric effect occurs according to the animation?

• A. Low atomic number tissue
• B. High atomic number tissue
• C. High water content tissue
• D. Low density tissue

Answer: (B)

The key idea is that the photoelectric effect depends strongly on the atomic number of the material. Materials with higher atomic number have a much greater probability of undergoing photoelectric absorption at typical diagnostic X-ray energies, because the interaction scales with a high power of Z. In medical imaging, bone contains calcium and other higher-Z elements, so it absorbs more photons via the photoelectric effect than soft tissues, which are made of lighter elements. That’s why the tissue with high atomic number is the one where the photoelectric effect is most likely to occur. The other properties—lower atomic number, high water content, or lower density—do not enhance the photoelectric interaction as much at these energies, so they’re not the best descriptors for where this effect predominates.

The key idea is that the photoelectric effect depends strongly on the atomic number of the material. Materials with higher atomic number have a much greater probability of undergoing photoelectric absorption at typical diagnostic X-ray energies, because the interaction scales with a high power of Z. In medical imaging, bone contains calcium and other higher-Z elements, so it absorbs more photons via the photoelectric effect than soft tissues, which are made of lighter elements. That’s why the tissue with high atomic number is the one where the photoelectric effect is most likely to occur. The other properties—lower atomic number, high water content, or lower density—do not enhance the photoelectric interaction as much at these energies, so they’re not the best descriptors for where this effect predominates.