Experiments searching for rare processes like neutrinoless double beta decay heavily rely on the identification of background events to reduce their background level and increase their sensitivity. ...We present a novel machine learning based method to recognize one of the most abundant classes of background events in these experiments. By combining a neural network for feature extraction with a smaller classification network, our method can be trained with only a small number of labeled events. To validate our method, we use signals from a broad-energy germanium detector irradiated with a
228
Th gamma source. We find that it matches the performance of state-of-the-art algorithms commonly used for this detector type. However, it requires less tuning and calibration and shows potential to identify certain types of background events missed by other methods.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Events from alpha interactions on the surfaces of germanium detectors are a major contribution to the background in germanium-based searches for neutrinoless double-beta decay. Surface events are ...subject to charge trapping, affecting their pulse shape and reconstructed energy. A study of alpha events on the passivated end-plate of a segmented true-coaxial n-type high-purity germanium detector is presented. Charge trapping is analysed in detail and an existing pulse-shape analysis technique to identify alpha events is verified with mirror pulses observed in the non-collecting channels of the segmented test detector. The observed radial dependence of charge trapping confirms previous results. A dependence of the probability of charge trapping on the crystal axes is observed for the first time. A first model to describe charge trapping effects within the framework of the simulation software
SolidStateDetectors.jl
is introduced. The influence of metalisation on events from low-energy gamma interactions close to the passivated surface is also presented.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The GERmanium Detector Array (GERDA) experiment searched for the lepton-number-violating neutrinoless double-β (0νββ) decay of ^{76}Ge, whose discovery would have far-reaching implications in ...cosmology and particle physics. By operating bare germanium diodes, enriched in ^{76}Ge, in an active liquid argon shield, GERDA achieved an unprecedently low background index of 5.2×10^{-4} counts/(keV kg yr) in the signal region and met the design goal to collect an exposure of 100 kg yr in a background-free regime. When combined with the result of Phase I, no signal is observed after 127.2 kg yr of total exposure. A limit on the half-life of 0νββ decay in ^{76}Ge is set at T_{1/2}>1.8×10^{26} yr at 90% C.L., which coincides with the sensitivity assuming no signal.
A novel Compton Scanner setup has been built, commissioned and operated at the Max-Planck-Institute for Physics in Munich to collect pulses from bulk events in high-purity germanium detectors for ...pulse shape studies. In this fully automated setup, the detector under test is irradiated from the top with 661.660 keV gammas, some of which Compton scatter inside the detector. The interaction points in the detector can be reconstructed when the scattered gammas are detected with a pixelated camera placed at the side of the detector. The wide range of accepted Compton angles results in shorter measurement times in comparison to similar setups where only perpendicularly scattered gammas are selected by slit collimators. In this paper, the construction of the Compton Scanner, its alignment and the procedure to reconstruct interaction points in the germanium detector are described in detail. The creation of a first pulse shape library for an n-type segmented point-contact germanium detector is described. The spatial reconstruction along the beam axis is validated by a comparison to measured surface pulses. A first comparison of Compton Scanner pulses to simulated pulses is presented to demonstrate the power of the Compton Scanner to test simulation inputs and models.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
The electron drift in germanium detectors is modeled making
many assumptions. Confronted with data, these assumptions have to be
revisited. The temperature dependence of the drift of ...electrons was
studied in detail for an n-type segmented point-contact germanium
detector. The detector was mounted in a temperature controlled,
electrically cooled cryostat. Surface events were induced with
collimated 81 keV photons from a
133
Ba source. A detailed
analysis of the rise time of pulses collected in surface scans,
performed at different temperatures, is presented. The longitudinal
anisotropy of the electron drift decreases with rising
temperature. A new approach, making use of designated rise-time
windows determined by simulations using
SolidStateDetectors.jl
, was used to isolate the longitudinal
drift of electrons along different axes to quantify this
observation. The measured temperature dependence of the longitudinal
drift velocities combined with the standard electron-drift model as
widely used in relevant simulation packages results in unphysical
predictions. A modification of the electron-drift model based on
assuming phonons to be the dominating scattering centers for
electrons is motivated and described. The results of a first
implementation of the modified model in
SolidStateDetectors.jl
are shown. They describe the
temperature dependence of the data reasonably well. A general review
of the model and the standard input values for mobilities is
suggested.
Abstract
The open-source software package
SolidStateDetectors.jl
to calculate the fields and simulate
the drifts of charge carriers in solid state detectors, especially
in large volume high-purity ...germanium detectors, together with the
corresponding pulses, is introduced. The package can perform all
calculations in full 3D while it can also make use of detector
symmetries. The effect of the surroundings of a detector can also be
studied. The package is programmed in the user friendly and
performance oriented language julia, such that 3D field
calculations and drift simulations can be executed efficiently and
in parallel. The package was developed for high-purity germanium
detectors, but it can be adjusted by the user to other types of
semiconductors. The verification of the package is shown for an
n-type segmented point-contact germanium detector. Additional
features of
SolidStateDetectors.jl
, which are under
development are listed.
The objective of the work was to investigate the possibility of using a tricresyl phosphate-based carbon paste electrode for the direct voltammetric determination of the neonicotinoid insecticide ...thiamethoxam. The analyte was determined by differential pulse voltammetry in Britton-Robinson buffer pH 7.0 in the concentration range of 3.72 - 41.5 ?g mL-1. The reproducibility of the analytical signal at the 7.29 ?g mL-1 level was characterized by a relative standard deviation of 1.3 %. The applicability of the developed method was evaluated by determining thiamethoxam in a river water sample and a commercial formulation Actara 25 WG.
A simple first-order derivative spectrophotometric method was developed for
the simultaneous determination of acetamiprid and 6-chloronicotinic acid
(6-CNA) at pH 7.0. By using the zero-crossing ...approach, acetamiprid was
determined at 269.0 nm and 6-CNA at 216.0 nm with the detection limits of
7.19x10-7 and 8.25x10-7 mol dm-3, respectively and relative standard
deviations not exceeding 1.2% in the case of model systems.
nema
A simple first-order derivative spectrophotometric method was developed for the simultaneous determination of imidacloprid and 6-chloronicotinic acid (6-CNA). By using the zero-crossing approach, ...imidacloprid was determined at 249 nm and 6-CNA at 236 nm with detection limits of 0.32 and 0.17 ?g mL-1, respectively, and relative standard deviations not exceeding 1.2 % in the case of model systems. The proposed method was applied for the determination of imidacloprid and 6-CNA in commercial formulations. A conventional spectrophotometric method (at 270 nm) was also employed for the determination of the content of imidacloprid in the same commercial formulations. The results of the developed spectrophotometric methods were in good agreement with those obtained by the high-performance liquid chromatographic method.
Predlozena je jednostavna spektrofotometrijska metoda na bazi prvog izvoda za istovremeno odredjivanje imidakloprida i 6-hlornikotinske kiseline (6-HNK). Primenjujuci pristup nultog preseka imidakloprid je odredjivan u model sistemu na 249 nm a 6-HNK na 236 nm, sa granicama detekcije od 0,32 i 0,17 ?g mL-1, respektivno i relativnom standardnom devijacijom manjom od 1,2 %. Predlozena metoda je primenjena za odredjivanje imidakloprida i 6-HNK u komercijalnim preparatima. Konvencionalna spektrofotometrijska metoda (na 270nm) je takodje primenjena za odredjivanje sadrzaja imidakloprida u istim komercijalnim preparatima. Rezultati predlozene spektrofotometrijske metode su u dobroj saglasnosti sa rezultatima dobijenim metodom tecne hromatografije visoke efikasnosti.
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