Assessment of material radiopurity for Rare Event experiments using Micromegas

Abstract

Micromesh gas amplification structures (Micromegas) can beused as readout of Time Projection Chambers in the field of RareEvent searches dealing with dark matter, double beta decay or solaraxions. The topological information of events offered by thesegaseous detectors is a very powerful tool for signal identificationand background rejection. However, in this kind of experiments theradiopurity of the detector components and surrounding materialsmust be thoroughly controlled in addition in order to keep theexperimental background as low as possible.A screening program based mainly on gamma-ray spectrometry using anultra-low background HPGe detector in the Canfranc UndergroundLaboratory is being developed for several years, with the aim tomeasure the activity levels of materials used in the Micromegasplanes and also in other components involved in a plausibleexperimental set-up: gas vessel, field cage, electronic boards,calibration system or shielding.The techniques and equipment used in these measurements will bedescribed and the main results will be presented and discussed. Inparticular, first results for the activity of Micromegas readouts ofthe microbulk type produced at CERN indicate that they are alreadycomparable to the cleanest readout systems in low backgroundexperiments and it should be possible to further improve theselevels after dedicated development.