Energy per ion pair for electrons in gases and gas mixtures

The energy expenditure per ion pair, V, for electrons in argon, helium, hydrogen, nitrogen, air, oxygen and methane is determined using ion chambers and proportional counters with terminals which correct for 'end-effect'. Experiments using $^{37}$ A and tritium as sources of ionizing electrons are performed. Curves of ion current against percentage of argon admixed with the other gases are plotted. The variation of V with energy of the ionizing electrons is investigated for nitrogen between the limits 200 eV and 46$\cdot $7 keV for the primary electrons and only a small variation is found. The ratio V gas/V argon is given in each case and is found to be almost identical to the corresponding ratio for ionization by 340 MeV protons. Examination of previous work with $\alpha $-particles suggests close agreement with the values for electrons and protons.