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Light Collection Uniformity

The proper surface treatment of the each of the modules as it affects the light output and the light collection uniformity along the longitudinal axis of the crystal has been investigated. Different wrapping materials have been tested for maximum light output and minimum non-uniformity. One of the crystals has been studied in beam and with cosmic rays using the various surface treatments. These studies have resulted in a convergence upon the following wrapping method: three layers of teflon ( thick) plus one layer of aluminized mylar () on the lateral surface with back paper on the front face. Prior to the wrapping, each crystal is polished using a mixture of aluminium oxide power and ethylene glycol. However, other surface treatments are currently under investigation. In addition, a cosmic ray tomography system has been designed to measure the light collection non-uniformity throughout the entire volume of each module. In particular, this method will reveal the regions of impurities and imperfections where the scintillation light is absorbed. For each of the crystals which eventually will make up the calorimeter, the non-uniformity must be . Once the crystals have been tested for F/T and their dimensions checked, they are wrapped as described above and passed on to the tomography system. The description of the tomography apparatus and some of its results will be presented in a subsequent chapter.

Bernward Krause
Mon Jan 15 14:57:06 MET 1996