While developing a liquid argon detector for dark matter searches we investigate the influence of air contamination on the VUV scintillation yield in gaseous argon at atmospheric pressure. We determine with a radioactive αsource the photon yield for various partial air pressures and different reflectors and wavelength shifters. We find for the fast scintillation component a time constant τ1 = 11.3 ± 2.8 ns, independent of gas purity. However, the decay time of the slow component depends on gas purity and is a good indicator for the total VUV light yield. This dependence is attributed to impurities destroying the long-lived argon excimer states. The population ratio between the slowly and the fast decaying excimer states is determined for α-particles to be 5.5 ± 0.6 in argon gas at 1100 mbar and room temperature. The measured mean life of the slow component is τ2 = 3.140 ± 0.067 µs at a partial air pressure of 2 × 10 −6 mbar.

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Large area avalanche photodiodes (LAAPDs) were used for a series of systematic measurements of the scintillation light in Ar, Kr, and Xe gas. Absolute quantum efficiencies are derived. Values for Xe and Kr are consistent with those given by the manufacturer. For the first time we show that argon scintillation (128 nm) can be detected at a quantum efficiency above 40%. Low-pressure argon gas is shown to emit significant amounts of non-UV radiation. The average energy expenditure for the creation of non-UV photons in argon gas at this pressure is measured to be below 378 eV. r

Abstract-The possibility of efficient collection and detection of vacuum ultraviolet light as emitted by argon, krypton, and xenon gas is studied. Absolute quantum efficiencies of large area avalanche photodiodes (LAAPDs) are derived at these wavelengths. VUV light of wavelengths down to the 128nm of Ar emission is shown to be detectable with silicon avalanche photodiodes at quantum efficiencies above 42%. Flexible Mylar foil overcoated with Al+MgF2 is measured to have a specular reflectivity of ∼91% at argon emission wavelength. Low-pressure argon gas is shown to emit significant amounts of non-UV radiation. The average energy expenditure for the creation of non-UV photons in argon gas at this pressure is measured to be below 378 eV.Index Terms-VUV light, APD, argon scintillation, quantum efficiency, Al+MgF2.