In this paper we report on measurements of the effects of dissolved methane
upon argon scintillation light. We monitor the light yield from an alpha source
held 20 cm from a cryogenic photomultiplier tube (PMT) assembly as methane is
injected into a high-purity liquid argon volume. We observe significant
suppression of the scintillation light yield by dissolved methane at the 10
part per billion (ppb) level. By examining the late scintillation light time
constant, we determine that this loss is caused by an absorption process and
also see some evidence of methane-induced scintillation quenching at higher
concentrations (50-100 ppb). Using a second PMT assembly we look for visible
re-emission features from the dissolved methane which have been reported in
gas-phase argon methane mixtures, and we find no evidence of visible
re-emission from liquid-phase argon methane mixtures at concentrations between
10 ppb and 0.1%.Comment: 18 pages, 11 figures Updated to match published versio
