Signal modeling of high-purity Ge detectors with a small read-out electrode and application to neutrinoless double beta decay search in Ge-76

The Gerda experiment searches for the neutrinoless double beta decay of super(76)Ge using high-purity germanium detectors enriched in super(76)Ge. The analysis of the signal time structure provides a powerful tool to identify neutrinoless double beta decay events and to discriminate them from gamma-...

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Bibliographic Details
Published in:Journal of instrumentation 2011-03, Vol.6 (3), p.P03005-27
Main Authors: Agostini, M, Ur, C A, Budjáš, D, Bellotti, E, Brugnera, R, Cattadori, C M, Vacri, A di, Garfagnini, A, Pandola, L, Schönert, S
Format: Article
Language:English
Subjects:
Beta decay
Computer simulation
Decay
Detectors
Electrodes
Mathematical models
Pulse shape
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Summary:The Gerda experiment searches for the neutrinoless double beta decay of super(76)Ge using high-purity germanium detectors enriched in super(76)Ge. The analysis of the signal time structure provides a powerful tool to identify neutrinoless double beta decay events and to discriminate them from gamma-ray induced backgrounds. Enhanced pulse shape discrimination capabilities of Broad Energy Germanium detectors with a small read-out electrode have been recently reported. This paper describes the full simulation of the response of such a detector, including the Monte Carlo modeling of radiation interaction and subsequent signal shape calculation. A pulse shape discrimination method based on the ratio between the maximum current signal amplitude and the event energy applied to the simulated data shows quantitative agreement with the experimental data acquired with calibration sources. The simulation has been used to study the survival probabilities of the decays which occur inside the detector volume and are difficult to assess experimentally. Such internal decay events are produced by the cosmogenic radio-isotopes super(68)Ge and super(60)Co and the neutrinoless double beta decay of super(76)Ge. Fixing the experimental acceptance of the double escape peak of the 2.614 MeV photon to 90%, the estimated survival probabilities at Q sub( beta beta ) = 2.039 MeV are (86 plus or minus 3)% for super(76)Ge neutrinoless double beta decays, (4.5 plus or minus 0.3)% for the super(68)Ge daughter super(68)Ga, and (0.9 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(4) sub(2))% for super(60)Co decays.
ISSN:1748-0221
1748-0221
DOI:10.1088/1748-0221/6/03/P03005