Heavy Fluoride Glasses as an Alternative to Crystals in High Energy Physics Calorimetry
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ABSTRACT In the quest for low cost scintillators to equip the very large electromagnetic calorimeters for future High Energy Physics experiments, scintillating glasses can offer an attractive alternative to crystals. The expected production price is indeed supposed to be reduced as compared to crystals, especially for very large volumes. An intense R&D effort has been made by the Crystal Clear collaboration to develop heavy scintillating fluoride glasses in close collaboration with the industry. Results will be shown on the fluorescence and scintillation properties as well as on the radiation resistance of different types of fluoride glasses. Ideas about possible improvement of present performances will also be given. INTRODUCTION The search for heavy scintillators had a spectacular development in the last few years due to the large scale experiments planned in High Energy Physics. Only a few monocrystals are known today to fit the very tough conditions required by electromagnetic calorimetry in High Energy Physics: high density, low decay time, high radiation hardness. The Crystal Clear collaboration has developed a new type of cerium doped fluoride glasses as a possible alternative to crystal scintillators. Their main advantages are the possibility to be cast in any shape and the well developed industrial base for manufacturing them in a large scale.
EXPERIMENTAL FACILITIES All glasses studied in our work were produced by the company "Le Verre Fluor6" in France. More than 40 samples of different dimensions were analysed. Optical transmission spectra before and after irradiation were recorded in the range of 200 to 700 nm on a spectrophotometer built at CERN, using a 150W Xenon lamp as a source and a Jobin-Yvon H20UV monochromator with a resolution of 2 nm. Samples were irradiated with the 60Co source (4400Ci) from the radiotherapy unit of Geneva Cantonal Hospital, with different radiation dose steps at a dose rate of 3 Gy/min. Photoluminescence spectra were recorded on a JY3C-JOBIN YVON spectrofluorometer. The scintillation decay characteristics were determined on a classical single photon method [1] bench with a 22Na (1.6MBq) radiation source. Besides normal 217 Mat. Res. Soc. Symp. Proc. Vol. 348. 01994 Materials Research Society
measurements, a JOBIN YVON H20 UVL monochromator was included in the bench for the spectral analyse of the decay time. The decay time curves obtained in this case were also used to extract the radio luminescence spectra, which were corrected with the quantum efficiency of the R1668 PHILIPS photomultiplier (PM) used to detect the scintillation from the crystal. Due to the sharp decrease of quantum efficiency of the PM, the luminescence emission above 600 nm is not "seen" in our measurements. For the light yield (LY) measurements the samples were wrapped with a 12 prm thick reflective sheet of aluminised mylar and optically coupled to a quartz window XP2020Q Philips PM by an optical grease 47V Rhodorsil from Rh6nePoulenc. The fluorescence produced by gamma rays from a 137Cs radioactiv
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