Development of Endcap Electromagnetic Calorimete for B Factory

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The performance of CsI (Tl) single crystal was test for the use of high precision electromagnetic calorimeter for the BELLE experiment at the KEK asymmetric B-Factory. The radiation hardness of 30cm long crystal from Russian, Chinese and French crystal growers was tested by irradiating them by low energy gamma rays from ^<60>Co and measuring the change of average light yield and the uniformity of light collection. The radiation hardness of Chinese crystal was greatly improved by the doping of specific material. The crystals from all the vendors were finally proved to be adequate for the use in the endcap region. It was discovered that the localized radiation damage does not deteriorate the uniformity of the ligh yield, and therefore the decrease of average light yield is correctable by the calibration without sacrificing the energy resolution.We built automated optical and dimensional property measurement devices, and installed them in the crystal growth factories in Russia and China as well as at KEK for the final acceptance test of produced crystals. These devices measure the light yield and uniformity within 4 minutes, and the dimension of the crystal within 3 minutes.The performance of 6*6 crystal matrix was tested by the tagged photon beam at the Budker Institute of Nuclear Physics in Novosibirsk, Russia. The preliminary analysis shows an excellent energy resolution of 4.0% at 40MeV and 1.8% at 800 MeV.A study will be continued for improving the performance against pileup by adopting the wave form sampling technique.