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Choice of the radiator gas for the Cerenkov detector

The choice of the radiator gas has to take into account two requirements :

• High electron detection efficiency.
• Low pion detection efficiency.

Initially Freon-12 was assumed to be the gas of choice for the Cerenkov detector. We will therefore compare gas properties relative to Freon-12.

• Mean number of photo-electrons.
• Detector efficiency dependence on the gas refraction index
• Transparency of radiator gases
• Efficiency of pion detection.