Response of an α source mounted in a liquid argon ionization cell and read out in full charge collection mode

The total charge response curve of an 241Am source placed in a liquid argon ionization cell has been measured. In a pure liquid argon sample (O2 concentration <0.1 ppm), it can be described by a semi-empirical formula which is derived from a model formerly elaborated by Thomas and Imel. The validity of this new formula was also tested in the case of oxygen-polluted liquid argon. The agreement with the data seems to indicate that the initial ion–electron pair recombination factor is not affected when the O2 concentration is smaller than 7 ppm. Further use of our recombination factor parameterization has been made to analyze data of liquid argon purity monitors utilizing 241Am sources with a sensitivity to O2 concentrations of ∼0.1 ppm.