CsI scintillation layer uses a columnar structure to focus which type of photons?

• A. Columns Which Focus X-Rays Photons
• B. Squares Which Focus X-Rays Photons
• C. Columns Which Focus Light Photons
• D. Squares Which Focus Light Photons

Answer: (C)

Columnar CsI acts as an optical light guide. When X-rays interact in the CsI, they produce scintillation photons in the visible range. The needle-like columns channel those light photons along their length by internal reflection, directing them toward the photodetector and helping preserve spatial detail. X-ray photons themselves aren’t being focused by the columns; they’re absorbed and converted into light within the material. So the structure is designed to focus light photons, not X-rays.