Pulse shape analysis of scintillation signals from pure andxenon-doped liquid argon for radioactive background identification

Abstract

The response of a 19 kg active mass liquid argonscintillation detector to gamma, alpha and neutron radiation and itscharacteristic scintillation photon time distribution has been studiedin the framework of the Gerda double beta decay research anddevelopment program. The achieved photo-electron yield of 1.24 pe/keVwas stable during the two years of operation. The detector exhibitsexcellent energy resolution of 8.7/17.2 keV (σ) for gammaenergies of 60/239 keV. Radon was loaded into the liquid argon tostudy alpha energy quenching and decay time correlation of itsprogenies. A robust pulse shape analysis method was used to identifyand discriminate amongst the different radiation types. 60 keV gammasignals could be discriminated against neutron recoils of the samevisible energy with a miss-identification probability of < 5 · 10−4 limited by statistics and ambient backgrounds. Xenon dopingof liquid argon increased the photo-electron yield and improved thespectroscopic performance of the detector leading to an energyresolution of 7.2/15.4 keV (σ) for 60/239 keV. Thediscrimination power improved slightly with the addition of xenon up to concentrations of 300 ppm. Applications for background identification anddiscrimination in double beta decay search with 76Ge crystals, aswell as for Dark Matter search with liquid argon are discussed.