Study on electro-magnetic calorimeter with lead fluorite crystal

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The purpose of the present study is to establish the method to make lead fluoride crystal and to find application to calorimetric detector of the high energy particle. Since lead-fluoride crystal has no scintillation, it will be used as a Cherenkov radiator. The properties of lead fluoride are quite different from those of lead-glass which is widely used. It has heavier density, larger refractive index and better transparency in short wave length of light and has been expected to improve high-energy calorimetric detection using Cherenkov light. Ai first we studied the fabrication method of lead fluoride crystal and finally obtained nine samples of 2 X 2 X 10 cm^3. They are very transparent and show a good property comparable to the world best crystals. We found also non-easiness for fabrication of large crystal. Most of samples are broken during polish. This is due to the fact that an internal stress remains after the process of cool-down from high temperature to grow crystal. Since lead fluoride has two different crystal structures in high and room temperature, two structure can co-exist in one crystal for the cool-down crystals. We tried to find a method to avoid the co-existence by changing the cool-down speed, but the best way has not yet been established. For the nine samples, we performed a test using a high energy beam of electrons, pions and muons in November 2001. The data are being analyzed now. Moreover, we studied a possibility to use as a tool to separate neutron and gamma of GeV energy by stacking scintillator and cherenkov radiators. Lead fluorite is a possible candidate of the cherenkov radiator. The results of its model test was published.