Influence of the gas composition on the electron transport coefficients in helium-based gas mixtures

For several helium–isobutane and helium–methane gas mixtures the drift velocity and the longitudinal and transversal diffusion coefficients have been measured with a time of flight method using single-drift electrons. The influence of the hydrocarbon, water and nitrogen content in the gas mixture on the transport coefficients was studied in detail for concentrations typical for the operation of drift chambers.