STUDIES OF HELIUM GAS-MIXTURES IN DRIFT CHAMBERS

Some properties of gas mixtures composed predominately of helium and lesser amounts of CO2 and isobutane were measured in a prototype drift chamber. The studies are motivated by the desire to reduce the multiple scattering inside the drift chamber at future high-luminosity, low-energy facilities such as phi-factories, tau/charm factories, and B factories. The low atomic number of helium greatly reduces the multiple scattering contribution to the momentum resolution compared to an argon-based gas mixture. The position resolution, pulse height, efficiency, and breakdown characteristics were measured for various gas mixtures. A mixture of 83% He, 10% CO2, and 7% isobutane gives comparable results to that of an argon-based gas commonly used in drift chambers.