The effect of electric field non-uniformities on the measured value of Townsend's α †

It is not possible with any electrode system to produce a perfectly uniform electric field and the departures from uniformity may producer errors in the measured values of Townsend's first and second ionization coefficients. Calculations are reported giving the magnitude of the errors in the first coefficient,α, for helium, hydrogen, nitrogen and methane at low E/p, where the errors reach a maximum, for Bruce and other electrode systems. An experimental method of detecting errors in α from this source is proposed and a theoretical equation is presented relating the error in α. to the maximum field non-uniformity.