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 4 factories, T/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. Submitted to Nuclear Instruments and Methods A *Work supported by Department of Energy contracts DE-AC03-76SF00515 (SLAC) and DE-AM03-76SFOOOlO (UCSC).