364 Chapter 6. Scintillation Detectors and Photodetectors
Radiation
Incident
θt
θi θr
Scintillation Photons
θp
θt
θp
θr
(Since )θr=θi
=>θp=π 2 −θr+θt
θp π
2
θi θt
π
2
−θr
π
2
π
2
θr θp π
2
θt+ π θp
2
π
2
θt
Scintillator
Light Guide
Photodetector
Or = − +
− + − + =π −
+
Figure 6.4.2: Transmission of scintillation photons through a fish-tail light
guide to a photodetector. Also shown is the derivation ofθpas a function
of the angle of incidenceθiand the tapering angleθt.
Example:
The scintillation material of a radiation detector is to be connected with a
photomultiplier tube through a fish-tail type light guide. Assume that the
light guide has a refractive index of 1.5 and the system will be used in air.