209 research outputs found
Measurement of the temperature dependence of pulse lengths in an n-type germanium detector
The temperature dependence of the pulse length was measured for an 18-fold
segmented n-type germanium detector in the temperature range of 77-120 K. The
interactions of 122 keV photons originating from a Europium-152 source were
selected and pulses as observed on the core and segment electrodes were
studied. In both cases, the temperature dependence can be well described by a
Boltzmann-like ansatz.Comment: 17 pages, 2 tables, 13 figures, published in EPJ A
Signal recognition efficiencies of artificial neural-network pulse-shape discrimination in HPGe -decay searches
A pulse-shape discrimination method based on artificial neural networks was
applied to pulses simulated for different background, signal and signal-like
interactions inside a germanium detector. The simulated pulses were used to
investigate variations of efficiencies as a function of used training set. It
is verified that neural networks are well-suited to identify background pulses
in true-coaxial high-purity germanium detectors. The systematic uncertainty on
the signal recognition efficiency derived using signal-like evaluation samples
from calibration measurements is estimated to be 5\%. This uncertainty is due
to differences between signal and calibration samples
Axes determination for segmented true-coaxial HPGe detectors
A fast method to determine the crystallographic axes of segmented
true-coaxial high-purity germanium detectors is presented. It is based on the
analysis of segment-occupancy patterns obtained by irradiation with radioactive
sources. The measured patterns are compared to predictions for different axes
orientations. The predictions require a simulation of the trajectories of the
charge carriers taking the transverse anisotropy of their drift into account.Comment: 18 pages, 1 table, 31 figures; included background contribution to
the occupancy patterns and systematic uncertainties, results slightly change
Aluminum as a source of background in low background experiments
Neutrinoless double beta decay would be a key to understanding the nature of
neutrino masses. The next generation of High Purity Germanium experiments will
have to be operated with a background rate of better than 10^-5 counts/(kg y
keV) in the region of interest around the Q value of the decay. Therefore, so
far irrelevant sources of background have to be considered. The metalization of
the surface of germanium detectors is in general done with aluminum. The
background from the decays of 22Na, 26Al, 226Ra and 228Th introduced by this
metalization is discussed. It is shown that only a special selection of
aluminum can keep these background contributions acceptable.Comment: 11 pages, 3 Tables, 11 Figures, accepted for publication in NIM
The background in the neutrinoless double beta decay experiment GERDA
The GERmanium Detector Array (GERDA) experiment at the Gran Sasso underground
laboratory (LNGS) of INFN is searching for neutrinoless double beta decay of
76Ge. The signature of the signal is a monoenergetic peak at 2039 keV, the
Q-value of the decay, Q_bb. To avoid bias in the signal search, the present
analysis does not consider all those events, that fall in a 40 keV wide region
centered around Q_bb. The main parameters needed for the neutrinoless double
beta decay analysis are described. A background model was developed to describe
the observed energy spectrum. The model contains several contributions, that
are expected on the basis of material screening or that are established by the
observation of characteristic structures in the energy spectrum. The model
predicts a flat energy spectrum for the blinding window around Q_bb with a
background index ranging from 17.6 to 23.8*10^{-3} counts/(keV kg yr). A part
of the data not considered before has been used to test if the predictions of
the background model are consistent. The observed number of events in this
energy region is consistent with the background model. The background at Q-bb
is dominated by close sources, mainly due to 42K, 214Bi, 228Th, 60Co and alpha
emitting isotopes from the 226Ra decay chain. The individual fractions depend
on the assumed locations of the contaminants. It is shown, that after removal
of the known gamma peaks, the energy spectrum can be fitted in an energy range
of 200 kev around Q_bb with a constant background. This gives a background
index consistent with the full model and uncertainties of the same size
Status of the GERDA experiment
The study of neutrinoless double beta (0nbb) decay is the only one presently known approach to the fundamental question if the neutrino is a Majorana particle, i.e. its own anti-particle. The observation of 0nbb decay would prove that lepton number is not conserved, establish that neutrino has a Majorana component and, assuming that light neutrino is the dominating process, provide a method for the determination of its effective mass. GERDA is a new 0nbb decay experiment which is currently taking data at the Laboratori Nazionali del Gran Sasso (LNGS) of INFN in Italy. It implements a new shielding concept by operating bare diodes made from Ge with enriched 76Ge in high purity liquid argon supplemented by a water shield. The aim of GERDA is to verify or refute the recent claim of discovery, and, in a second phase, to achieve a two orders of magnitude lower background index than past experiments, to increase the sensitive mass and to collect an exposure of 100 kg yr. The paper will discuss design, physics reach, and status of data taking of GERDA.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard
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