ICP MS Selection of Radiopure Materials for the GERDA Experiment

The GERDA (GERmanium Detector Array) experiment, located in the Gran Sasso Underground Laboratory (LNGS, Italy) aims to search for neutrinoless double beta (0 nu beta beta) decay of the Ge-76 isotope. Both an ultra-low radioactivity background environment and active techniques to abate the residual background are required to reach the background index (of 10(-3) counts/keV kg y) at the Q(beta beta). In order to veto and suppress those events that partially deposit energy in Ge detectors, the readout of liquid argon (LAr) scintillation light (SL) has been implemented for the second GERDA experimental Phase. A double veto system has been designed and constructed using highly radiopure materials (scintillating fibers, wavelength shifters, polymeric foils, reflective foils). This work describes the study of lead, thorium and uranium ultra-trace content, performed at the LNGS Chemistry Laboratory by High Resolution Mass Spectrometry (HR ICP MS), for the selection of all materials involved in the construction of the veto system