Effect of air on gas amplification characteristics in argon-propane (1%)-based proportional counters for airborne radon monitoring

Aiming for the development of a new technique of on-line airborne radon activity concentration measurement, the effect of air on some detection properties of argon-propane (1%)-based proportional counters is investigated when a fraction of 2%, 6% and 10% of it is successively and intentionally admixed to the counting gas in a single-wire proportional counter. The influence of the electron attachment, principally due to oxygen component, on the ionization saturation plateau and the gas amplification process is particularly examined. The previously developed semi-microscopic gas gain formula is found to describe well the gas gain data obtained in each of the gas mixtures analyzed, thus allowing a consistent examination of the air effect on the relevant gas constants. Finally, the possibility to use such air-mixed counting gases in specially designed gas-flow proportional counters intended for new on-line measurement methods of airborne radon (222Rn) activity concentration appeared quite viable.