A radioactive point-source lattice for calibrating and monitoring the liquid xenon calorimeter of the MEG experiment

Liquid scintillator calorimeters and in particular liquid cryogenic noble gas detectors can be calibrated and monitored by the use of multiple αα-sources distributed in the detector sensitive volume. For the MEG experiment we developed a method based on the use of Po210 and Am241 point sources deposited on thin (100μm diameter) gold-plated tungsten wires permanently suspended in the volume and fixed at the surfaces of the large vessel containing the LXe. The method is valuable in measuring the relative QEs of all PMTs surrounding the sensitive LXe volume, in determining the LXe optical properties for the UV scintillation light and in checking the stability of the calorimeter properties during the experiment.