Status of Underground Radioactivity Measurements in HADES

The IRMM (Institute for Reference materials and Measurements) performs ultra low-level gamma-ray spectrometry at a depth of 225 m in the underground laboratory HADES. The facility currently houses 7 HPGe-detectors that are built and shielded using specially selected radiopure materials. The sand-clay overburden of about 500 m water equivalent assures a muon flux reduction factor of about 5000, with subsequent reduction of the background of the detectors, which makes it possible to obtain detection limits close to 100 Bq for certain radionuclides. This paper describes the aim of the IRMM activities in the HADES laboratory, the equipment and the measurement program and gives examples of radiopurity measurements carried out in order to develop better low-level measurements.