A typical timehyphen;ofhyphen;flight electronhyphen;swarm experiment was modified by replacing the electrichyphen;fieldndash;ring assembly with a conducting paper cylinder in order to (1) increase the lateral dimension of the swarm region, and (2) remove nonconducting surfaces which become charged with electrons and thereby provide the zerohyphen;field condition necessary for thermal electron diffusion and capture studies in gases. A new driftndash;dwellndash;drift technique was devised whereby electron swarms were (1) drifted to the center of the swarm region, (2) allowed to dwell there for varying periods of time under fieldhyphen;free conditions, and then (3) drifted to the anode where proper sampling with a differentially pumped electronhyphen;multiplier detection system allowed the reconstruction of the swarm timehyphen;ofhyphen;arrival distribution. Diffusion coefficients were determined for thermal electron swarms in nine gases. The mean thermal diffusionhyphen;pressurelpar;DtPrpar;values were 0.214, 2.01, 0.885, 0.133, 0.294, 0.178, 0.0151, 0.253, and 0.281 cm2mgr;secminus;1torr for He, Ne, Ar, H2, N2, CO, CO2, CH4, and C2H4, respectively.
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