Development of light guides for the camera of CANGAROO-III telescope

Abstract

The camera of the CANGAROO-III Cherenkov telescope consists of many photomultiplier tubes(PMTs), with significant dead space between the PMTs. Light guides reflect photons directed at dead spaces, to the effective area of a PMT. We performed Monte Carlo simulations for various shapes of light guides to evaluate their performance, compared with experimental values, and determined the optimal shape of the light guide for the CANGAROO-III telescope. We calculated the light collection efficiency as a function of incident angle for various types of light guides using the Monte Carlo simulation. The best efficiency of the light guide was obtained for the following conditions: The cross sectional shape cut along the central axis of the light guide should have the Winston cone shape, though the entrance finestra is hexagonal, and the gap between the light guide and the PMT should be as small as possible. To decrease the energy threshold of CANGAROO-III telescope, good light collection efficiency is very important.