Maximization of argon-hydrocarbon Penning mixtures

Townsend's primary and secondary ionization coefficients have been measured in 0·003, 0·03, 0·3 and 3% of n -pentane, ethylene and acetylene mixed in argon for a total pressure in the range 0·5 to 500 torr and for a uniform field gap up to 1 cm. For n -pentane, a concentration of 15% was also employed. A marked Penning effect is again observed and is greatest in about 0·1% of acetylene in argon; the enhancement of Townsend's primary ionization coefficient in this mixture exceeds that previously observed in the classical rare gas mixtures. As usual, the hydrocarbons are observed to be efficient quenching agents, acetylene in this respect being the less efficient. At an optimum concentration of 0·03% for all the mixtures the sparking voltage is lowered considerably below that for pure argon, the lowering being the most - and amounting to a factor somewhat greater than 4 - in argon-acetylene mixtures.