Townsend's First Ionization Coefficient in Nitrogen

Measurements of Townsend's first ionization coefficient, α, have been made in nitrogen for values of E/p from 24 to 82. The ionization coefficient α is the mean number of ionizations per cm in the field direction produced by electron collision. E is the electric field strength measured in volts per cm and p is the pressure in mm of mercury. Sodium azide was used as a nitrogen source in an effort to obtain pure nitrogen. Data were also taken in tank nitrogen and mass spectrographic analyses of gas from both sources were made. No impurities were detectable in the sodium-azide-produced gas, while the tank nitrogen was found to contain some contamination even after a purification process. Results at low values of E/p differ considerably from previously reported data, while at high values the results agree very well with data obtained by Bowls. Values of αp in tank nitrogen were found to be considerably lower at low E/p than those found in gas produced from sodium azide, although at high values the difference was small. The effect of wall potential on αp was investigated and was found to be unimportant over a range from 45% to 100% of anode potential.