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Pulse shape discrimination studies with a Broad-Energy Germanium detector for signal identification and background suppression in the GERDA double beta decay experiment

Research paper by Dušan Budjáš, Marik Barnabé Heider, Oleg Chkvorets, Nikita Khanbekov, Stefan Schönert

Indexed on: 22 Sep '09Published on: 22 Sep '09Published in: Nuclear Experiment



Abstract

First studies of event discrimination with a Broad-Energy Germanium (BEGe) detector are presented. A novel pulse shape method, exploiting the characteristic electrical field distribution inside BEGe detectors, allows to identify efficiently single-site events and to reject multi-site events. The first are typical for neutrinoless double beta decays (0-nu-2-beta) and the latter for backgrounds from gamma-ray interactions. The obtained survival probabilities of backgrounds at energies close to Q(76Ge) = 2039 keV are 0.93% for events from 60Co, 21% from 226Ra and 40% from 228Th. This background suppression is achieved with 89% acceptance of 228Th double escape events, which are dominated by single site interactions. Approximately equal acceptance is expected for 0-nu-2-beta-decay events. Collimated beam and Compton coincidence measurements demonstrate that the discrimination is largely independent of the interaction location inside the crystal and validate the pulse-shape cut in the energy range of Q(76Ge). The application of BEGe detectors in the GERDA and the Majorana double beta decay experiments is under study.