Ionization processes in helium at pressures near to atmospheric

Determinations of primary α and secondary ω ionization coefficients in helium at pressures p 0 near to atmospheric and low values of E/p 0 ( E is the electric field) show that α/ p 0 = f ( E/p 0 ) and ω/α = ϕ( E/p 0 ) for 30 < p 0 d < 730 cm torr. The results obtained for ω/α and its dependence on E/p 0 are shown to be adequately accounted for on the basis of the assumption that the predominant secondary ionization process in helium at high pressures is the destruction of metastable states in the gas with the consequent production of non-resonance photons which liberate secondary electrons at the cathode.