Study of reflection and connection materials used for transmitting and condensing scintillation light by means of optical fiber

The commonly used γ-ray measurement method employs a technique of transmitting scintillation light to a photomultiplier tube (PMT) via an optical fiber. However, it is said that the light transmission efficiency in this technique reduces significantly depending on the transmission properties, particularly on the critical angle of the optical fiber. We performed experiments and Monte Carlo simulations to examine the extent of the decrease in the light transmission efficiency of a discrete γ-ray detector, which uses optical fibers for the connection of the PMT to a scintillator, relative to that of an integrated γ-ray detector, which connects the PMT directly to a scintillator. We also examined the effects of the reflection and connection materials on the light transmission efficiency. The results show that to improve the light transmission efficiency, it is useful to apply specular or diffuse reflectors appropriately to the side and bottom surfaces of the scintillator, and also to provide space (air layer) between the output surface of the scintillator and the input surface of the optical fiber without using grease. (author)