Ionization coefficients and sparking voltages from methane to butane

Townsend primary (α/p 0)T and secondary ionization coefficients have been measured and sparking voltages have been deduced for methane, ethane, propane and butane over the pressure range 1 to 400 torr corresponding to 26 ≲ E/p 0≲2000 and voltages up to 500 kV. Townsend's equation α/p 0 = A exp ( - Bp o/E) is found to be obeyed over the region 30≲E /p 0≲670 corresponding to a range of α/p 0 of ratio 1000: 1 and the constants A and B increase systematically with increase in molecular weight of the gases tested. Large electron avalanches have been measured exceeding exp (ad) = 108. The secondary ionization coefficient decreases, whilst the sparking voltage increases, with increase in molecular weight.