High Efficiency Gas Cherenkov Counter

A threshold type gas Cherenkov counter using CO2 and Freon 12 (CCl2F2) is constructed. The counting efficiency was measured for electrons of momentum 300 MeV/c as a function of gas pressure. The pressure was varied from vacuum to 6 kg/cm2 with Freon 12 and to 15 kg/cm2 with CO2. The maximum efficiency obtained is 99.3±0.5%. The velocity resolution δβ is estimated to be better than 3×10-3, which suffices to discriminate electrons from muons and pions produced by a 1.3 GeV electron synchrotron.