Development of wavelength shifter coated reflectors for the ArDM argon dark matter detector

Abstract

To optimise the design of the light readout in the ArDM 1-ton liquid argon dark matter detector, a rangeof reflector and WLS coating combinations were investigated in several small setups, where argon scintillation light was generated by radioactive sources in gas at normal temperature and pressure and shifted into the blue region by tetraphenyl butadiene (TPB). Various thicknesses of TPB were deposited by spraying and vacuum evaporation onto specular3MTM-foil and diffuse Tetratex® (TTX) substrates. Light yields of each reflector and TPB coating combination were compared. Reflection coefficients of TPB coated reflectors were independentlymeasured using a spectroradiometer in a wavelength range between200 and 650 nm.WLS coating on the PMT window was also studied. These measurements were used to define the parameters of the light reflectorsof the ArDM experiment. Fifteen large 120 × 25 cm2 TTX sheetswere coated and assembled in the detector. Measurements in argon gas are reported providing good evidence of fulfilling the light collectionrequirements of the experiment.