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

Abstract

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.

Triplet lifetime in gaseous argon

“…PMT cross talk), and this effect appears to approximately cancel out when evaluating the ratio. The discrepancy between our results and the value 5.5 ± 0.6 reported in reference [11] is largely due to their use of an alpha particle source, well known to produce more prompt light compared to our electronic recoil events. Also a longer lifetime is attained in our measurement, which effectively increases the late/(prompt+intermediate) ratio.…”

“…However, even with an impurity level at 1 ppm, the density effect alone can not explain the variation of triplet decay rates and lifetimes. A more complete explanation requires inclusion of the effects of impurities, which have been investigated by many groups [11] [12][13] [14]. Table 1.…”

Cold Atmospheric Pressure Plasma VUV Interactions With Surfaces: Effect of Local Gas Environment and Source Design

“…It is also possible that there are some contributions to this emission from impurities in the Ar gas flow. This Ar 2 * excimer state is created by a three‐body collision process involving argon metastable states . Emission from this species has been characterized by previous work, but the effect it has on surfaces has been limited to disinfection .…”

In-situ measurement of the scintillation light attenuation in liquid argon in the Gerda experiment

“…The creation ratio of singlet to triplet state is about 0.3 for electrons. While the transition of the singlet state is allowed (4 -7 ns), the triplet state is forbidden (1.0 -1.7 µs), resulting in different decay times [11].…”