Light pipe may be used to attach ________ to PMTs

• A. Crystal
• B. Light pipe
• C. Collimator
• D. Detector electronics

Answer: (A)

The main idea is optical coupling between the scintillation crystal and the photomultiplier tube. A light pipe (light guide) sits between the crystal and the PMT to transfer the light photons efficiently from the crystal to the PMT’s photosensitive surface. Because the light produced by the gamma interaction comes from the crystal, that crystal is what is attached to the PMT via the light pipe. The other options don’t fit this optical role: a collimator shapes the incoming radiation, and detector electronics are the readout hardware, not the light-collecting element connected by a light pipe.