The ratio of diffusion coefficient to mobility for electrons in nitrogen and hydrogen

The ratio of the electron diffusion coefficient to the mobility ( D /μ), which characterizes the mean energy of the particles, has been measured in nitrogen and hydrogen over the range 7< E/p <40 v cm −1 torr −1 (20°C). A brief description of the apparatus and technique is included. The solution of the diffusion equation has been analysed to study the effects of the finite size of the electron source and the presence of walls.