Properties of CsI(Tl) crystals and their optimization for calorimetry of high energy photons

A photomultiplier setup for precise relative CsI(Tl) crystal light yield and uniformity measurements is described. It is used for wrapping material studies to optimize the uniformity and the yield of the light output of 36 cm long crystals. The uniformity is an important property in high energy photon calorimetry. Results of an optimization of photodiode coupling to crystals, the influence of temperature and radiation damage to light and photoelectron yield are also presented.