Gamma-ray spectrometry of ultra low levels of radioactivity within the material screening program for the GERDA experiment

In present and future experiments in the field of rare events physics a background index of 10−3 counts/(keV kg a) or better in the region of interest is envisaged. A thorough material screening is mandatory in order to achieve this goal. The results of a systematic study of radioactive trace impurities in selected materials using ultra low-level gamma-ray spectrometry in the framework of the GERDA experiment are reported.