62 research outputs found
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 Ge-76
using high-purity germanium detectors enriched in Ge-76. 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 Ge-68 and Co-60 and the neutrinoless double
beta decay of Ge-76. Fixing the experimental acceptance of the double escape
peak of the 2.614 MeV photon to 90%, the estimated survival probabilities at
Qbb = 2.039 MeV are (86+-3)% for Ge-76 neutrinoless double beta decays,
(4.5+-0.3)% for the Ge-68 daughter Ga-68, and (0.9+0.4-0.2)% for Co-60 decays.Comment: 27 pages, 17 figures. v2: fixed typos and references. Submitted to
JINS
Highly Sensitive Gamma-Spectrometers of GERDA for Material Screening: Part 2
The previous article about material screening for GERDA points out the
importance of strict material screening and selection for radioimpurities as a
key to meet the aspired background levels of the GERDA experiment. This is
directly done using low-level gamma-spectroscopy. In order to provide
sufficient selective power in the mBq/kg range and below, the employed
gamma-spectrometers themselves have to meet strict material requirements, and
make use of an elaborate shielding system. This article gives an account of the
setup of two such spectrometers. Corrado is located in a depth of 15 m w.e. at
the MPI-K in Heidelberg (Germany), GeMPI III is situated at the Gran-Sasso
underground laboratory at 3500 m w.e. (Italy). The latter one aims at detecting
sample activities of the order ~0.01 mBq/kg, which is the current
state-of-the-art level. The applied techniques to meet the respective needs are
discussed and demonstrated by experimental results.Comment: Featured in: Proceedings of the XIV International Baksan School
"Particles and Cosmology" Baksan Valley, Kabardino-Balkaria, Russia, April
16-21,2007. INR RAS, Moscow 2008. ISBN 978-5-94274-055-9, pp. 233-238; (6
pages, 4 figures
Pulse shape discrimination studies with a Broad-Energy Germanium detector for signal identification and background suppression in the GERDA double beta decay experiment
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.Comment: 22 pages, 16 figures, submitted to JINST: JINST_018P_080
Pulse shape discrimination studies with a Broad-Energy Germanium detector for signal identification and background suppression in the GERDA double beta decay experiment
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.Comment: 22 pages, 16 figures, submitted to JINST: JINST_018P_080
Pulse shape discrimination studies with a Broad-Energy Germanium detector for signal identification and background suppression in the GERDA double beta decay experiment
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.Comment: 22 pages, 16 figures, submitted to JINST: JINST_018P_080
Mitigation of Ar/K background for the GERDA Phase II experiment
Background coming from the Ar decay chain is considered to be one of
the most relevant for the GERDA experiment, which aims to search of the
neutrinoless double beta decay of Ge. The sensitivity strongly relies on
the absence of background around the Q-value of the decay. Background coming
from K, a progeny of Ar, can contribute to that background via
electrons from the continuous spectrum with an endpoint of 3.5 MeV. Research
and development on the suppression methods targeting this source of background
were performed at the low-background test facility LArGe. It was demonstrated
that by reducing K ion collection on the surfaces of the broad energy
germanium detectors in combination with pulse shape discrimination techniques
and an argon scintillation veto, it is possible to suppress the K
background by three orders of magnitude. This is sufficient for Phase II of the
GERDA experiment
Highly sensitive gamma-spectrometers of GERDA for material screening: Part I
The GERDA experiment aims to search for the neutrinoless double beta-decay of
76Ge and possibly for other rare processes. The sensitivity of the first phase
is envisioned to be more than one order of magnitude better than in previous
neutrinoless double beta-decay experiments. This implies that materials with
ultra-low radioactive contamination need to be used for the construction of the
detector and its shielding. Therefore the requirements on material screening
include high-sensitivity low-background detection techniques and long
measurement times. In this article, an overview of material-screening
laboratories available to the GERDA collaboration is given, with emphasis on
the gamma-spectrometry. Additionally, results of an intercomparison of the
evaluation accuracy in these laboratories are presented.Comment: Featured in: Proceedings of the XIV International Baksan School
"Particles and Cosmology" Baksan Valley, Kabardino-Balkaria, Russia, April
16-21,2007. INR RAS, Moscow 2008. ISBN 978-5-94274-055-9, pp. 228-232; (5
pages, 0 figures
decay of Ge into excited states with GERDA Phase I
Two neutrino double beta decay of Ge to excited states of Se
has been studied using data from Phase I of the GERDA experiment. An array
composed of up to 14 germanium detectors including detectors that have been
isotopically enriched in Ge was deployed in liquid argon. The analysis
of various possible transitions to excited final states is based on coincidence
events between pairs of detectors where a de-excitation ray is
detected in one detector and the two electrons in the other.
No signal has been observed and an event counting profile likelihood analysis
has been used to determine Frequentist 90\,\% C.L. bounds for three
transitions: : 1.6 yr,
: 3.7 yr and : 2.3 yr. These bounds are more
than two orders of magnitude larger than those reported previously. Bayesian
90\,\% credibility bounds were extracted and used to exclude several models for
the transition
Results on decay with emission of two neutrinos or Majorons in Ge from GERDA Phase I
A search for neutrinoless decay processes accompanied with
Majoron emission has been performed using data collected during Phase I of the
GERmanium Detector Array (GERDA) experiment at the Laboratori Nazionali del
Gran Sasso of INFN (Italy). Processes with spectral indices n = 1, 2, 3, 7 were
searched for. No signals were found and lower limits of the order of 10
yr on their half-lives were derived, yielding substantially improved results
compared to previous experiments with Ge. A new result for the half-life
of the neutrino-accompanied decay of Ge with significantly
reduced uncertainties is also given, resulting in yr.Comment: 3 Figure
Characterization of 30 Ge enriched Broad Energy Ge detectors for GERDA Phase II
The GERmanium Detector Array (GERDA) is a low background experiment located
at the Laboratori Nazionali del Gran Sasso in Italy, which searches for
neutrinoless double beta decay of Ge into Se+2e. GERDA has
been conceived in two phases. Phase II, which started in December 2015,
features several novelties including 30 new Ge detectors. These were
manufactured according to the Broad Energy Germanium (BEGe) detector design
that has a better background discrimination capability and energy resolution
compared to formerly widely-used types. Prior to their installation, the new
BEGe detectors were mounted in vacuum cryostats and characterized in detail in
the HADES underground laboratory in Belgium. This paper describes the
properties and the overall performance of these detectors during operation in
vacuum. The characterization campaign provided not only direct input for GERDA
Phase II data collection and analyses, but also allowed to study detector
phenomena, detector correlations as well as to test the strength of pulse shape
simulation codes.Comment: 29 pages, 18 figure
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