Experimental Townsend Ionization Coefficients for Isopentane

Townsend α and γ values have been measured over the range 60≤E/p0≤3000 for isopentane using the dc method of measuring the ionization current. The experimental apparatus and procedure are described. It is shown that Townsend's law α/p0=A exp (—Bp0/E) is obeyed within 80≤E/p0≤500. Positive ion action at the cathode sets in at E/p0≥500. The results agree with previous breakdown measurements. It was found possible to follow the current growth due to ionization of the gas over a multiplication range exceeding eight orders of magnitude. The influence of space-charge distortion within single avalanches and that due to neighboring ones has been examined. No space-charge reduction of the avalanche multiplication was observed until eαd≥107.