A dedicated test of the effects of Oxygen contamination in liquid Argon hasbeen performed at the INFN-Gran Sasso Laboratory (LNGS, Italy) within the WArPR&D program. Two detectors have been used: the WArP 2.3 lt prototype and asmall (0.7 lt) dedicated detector, coupled with a system for the injection ofcontrolled amounts of gaseous Oxygen. Purpose of the test with the 0.7 ltdetector is to detect the reduction of the long-lived component lifetime of theArgon scintillation light emission at increasing O2 concentration. Data fromthe WArP prototype are used for determining the behavior of both the ionizationelectron lifetime and the scintillation long-lived component lifetime duringthe O2-purification process activated in closed loop during the acquisitionrun. The electron lifetime measurements allow to infer the O2 content of theArgon and correlate it with the long-lived scintillation lifetime data. Theeffect of Oxygen contamination on the scintillation light has been thusmeasured over a wide range of O2 concentration, spanning from about 10^-3 ppmup to about 10 ppm. The rate constant of the light quenching process induced byOxygen in LAr has been found to be k'(O2)=0.54+-0.03 micros^-1 ppm^-1.
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