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

TL;DR

This study examines how trace air contamination affects the VUV scintillation yield in gaseous argon, revealing that impurities reduce the slow component lifetime and overall light yield, which is crucial for dark matter detector performance.

Contribution

It provides the first detailed measurement of air impurity effects on scintillation decay times and light yield in gaseous argon at atmospheric pressure.

Findings

Fast component decay time is 11.3 ns, unaffected by impurities.

Slow component lifetime decreases with increasing air contamination.

Impurities significantly reduce the total VUV light yield.

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 alpha-source the photon yield for various partial air pressures and different reflectors and wavelength shifters. We find for the fast scintillation component a time constant tau1= 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 alpha-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 tau2 = 3.140 +- 0.067 microsec at a partial air pressure of 2 x 10-6 mbar.