Luminescence quenching of the triplet excimer state by air traces in gaseous argon

The influence of air contamination on the VUV scintillation yield in gaseous argon at atmospheric pressure is investigated. We determine with a radioactive alpha-source the photon yield for various partial air pressures and different reflectors and wavelength shifters. We find that the time constant of the slow scintillation component depends on gas purity and is a good indicator for the total VUV light yield, while the fast component is not affected. This dependence is attributed to impurities destroying the long-lived triplet argon excimer state. The population ratio between the slow and the fast decaying excimer states is determined for alpha-particles to be 5.5 +/- 0.6 in argon gas at 1100 mbar and room temperature. The measured decay time constant of the slow component is 3.140 +/- 0.067 mu s at a partial air pressure of 2 x 10(-6) mbar.