HEROICA: an underground facility for the fast screening of germanium detectors

Abstract

HEROICA (Hades Experimental Research Of Intrinsic CrystalAppliances) is an infrastructure to characterize germanium detectorsand has been designed and constructed at the HADESUnderground Research Laboratory, located in Mol (Belgium).Thanks to the 223 m overburden of clay and sand,the muon flux is lowered by four orders of magnitude.This natural shield minimizes theexposure of radio-pure germanium material to cosmic radiationresulting in a significant suppression of cosmogenic activation in thegermanium detectors.The project has been strongly motivated by a special production of germaniumdetectors for the GERDA experiment. GERDA, currently collecting data at theLaboratori Nazionali del Gran Sasso of INFN,is searching for the neutrinolessdouble beta decay of 76Ge. In the near future, GERDA will increase itsmass and sensitivity by adding new Broad Energy Germanium (BEGe) detectors.The production of the BEGe detectors is done at Canberra inOlen (Belgium), located about 30 km from the underground test site.Therefore, HADES is used both for storage of the crystals over night, duringdiode production, and for the characterization measurements.A full quality control chain has been setup and tested on the firstseven prototype detectors delivered by the manufacturerat the beginning of 2012.The screening capabilities demonstratethat the installed setup fulfills a fast and complete set of measurementson the diodes and it can be seen as a general test facilityfor the fast screening of high purity germanium detectors.The results are of major importance for a future massive productionand characterization chain of germanium diodes foreseen for a possiblenext generation 1-tonne double beta decay experiment with 76Ge.