真栄城 敦


   The camera of the CANGAROO-III Cherenkov Telescope is composed with many photomultiplier tubes(PMTs). It causes dead space between the PMTs. Light guides lead the incident photons which might come to the dead space, to the effective area of each PMT. We had applied the Monte Carlo simulation to various shapes of light guides to evaluate their performance, compared with experimental values, and decided 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. As a result, the best efficiency of the light guide was obtained for the following conditions. Cross sectional shape cut along the center line of the light guide should have the Winston Cone shape, though the entrance finestra is hexagonal. Gap between the light guide and the PMT should be as small as possible.
   Good light collection efficiency is very important to decrease the detectable energy threshold of Cangaroo-III telescope to around 200 GeV. It is very meaningful to observe this energy region to bridge TeV region observation by the Cherenkov/Air shower ground based detectors and GeV region observation by satellites.