P. Agnes et al. (DarkSide Collaboration) M. Wójcik, G. Zuzel & K. Pelczar

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http://dx.doi.org/10.1103/PhysRevD.93.081101

Abstract

Liquid argon is a bright scintillator with potent particle identification properties, making it an attractive target for direct-detection dark matter searches. The DarkSide-50 dark matter search here reports the first WIMP search results obtained using a target of low-radioactivity argon. DarkSide-50 is a dark matter detector, using a two-phase liquid argon time projection chamber, located at the Laboratori Nazionali del Gran Sasso. The underground argon is shown to contain Ar39 at a level reduced by a factor (1.4±0.2)×103 relative to atmospheric argon. We report a background-free null result from (2616±43)  kg d of data, accumulated over 70.9 live days. When combined with our previous search using an atmospheric argon, the 90% C.L. upper limit on the WIMP-nucleon spin-independent cross section, based on zero events found in the WIMP search regions, is 2.0×10−44  cm2 (8.6×10−44  cm2, 8.0×10−43  cm2) for a WIMP mass of 100  GeV/c2 (1  TeV/c2, 10  TeV/c2).

C. Galbiati, M. Misiaszek and N. Rossi

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http://dx.doi.org/10.1140/epja/i2016-16086-1

Abstract

In this report we describe the unique capabilities of the α/β discrimination of the Borexino experiment. This capability is the direct result of years of development aimed at the design of an experiment that could withstand contamination from α-emitting nuclides. The combination of the excellent α/β discrimination and of the excellent radiopurity of the detector permitted to extract information on the solar neutrino interactions in Borexino without interference from α particles.

Agostini M., Barnabé-Heider M., Budjáš D., Cattadori C., Gangapshev A., Gusev K., Heisel M., Junker M., Klimenko A., Lubashevskiy A., Pelczar K. , Schönert S., Smolnikov A., Zuzel G.

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http://dx.doi.org/10.1140/epjc/s10052-015-3681-5

Abstract

LArGe is a Gerda low-background test facility to study novel background suppression methods in a low-background environment, for future application in the Gerda experiment. Similar to Gerda, LArGe operates bare germanium detectors submersed into liquid argon (1 m^{3}, 1.4 tons), which in addition is instrumented with photomultipliers to detect argon scintillation light. The scintillation signals are used in anti-coincidence with the germanium detectors to effectively suppress background events that deposit energy in the liquid argon. The background suppression efficiency was studied in combination with a pulse shape discrimination (PSD) technique using a BEGe detector for various sources, which represent characteristic backgrounds to Gerda. Suppression factors of a few times 10^{3} have been achieved. First background data of LArGe with a coaxial HPGe detector (without PSD) yield a background index of (0.12−4.6) \times 10^{−2} cts/(keV kg year) (90 % C.L.), which is at the level of Gerda Phase I. Furthermore, for the first time we monitor the natural ^{42}Ar abundance (parallel to Gerda), and have indication for the 2\nu \beta \beta-decay in natural germanium. These results show the effectivity of an active liquid argon veto in an ultra-low background environment. As a consequence, the implementation of a liquid argon veto in Gerda Phase II is pursued.

N. Frodyma, K. Pelczar,  M. Wójcik

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http://dx.doi.org/10.1016/j.nima.2014.01.039

Abstract

The results of alpha spectrometric measurements of the activity of ²²²Rn daughters dissolved in liquefied nitrogen are presented. A direct detection method of ionized alpha-emitters from the ²²²Rn decay chain (²¹⁴Po and ²¹⁸Po) in a cryogenic liquid in the presence of an external electric field is shown. Properties of the radioactive ions are derived from a proposed model of ion production and transport in the cryogenic liquid. Ionic life-time of the ions was found to be on the order of 10 s in liquid nitrogen (4.0 purity class). The presence of positive and negative ions was observed.

M Agostini et al., (GERDA Collaboration), N. Frodyma, M. Misiaszek, K. Pelczar, M. Wojcik, G. Zuzel

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http://arxiv.org/abs/1306.5084

http://link.springer.com/article/10.1140/epjc/s10052-013-2583-7

Abstract

The GERDA experiment located at the LNGS searches for neutrinoless double beta (0\nu\beta\beta) decay of ^{76}Ge using germanium diodes as source and detector. In Phase I of the experiment eight semi-coaxial and five BEGe type detectors have been deployed. The latter type is used in this field of research for the first time. All detectors are made from material with enriched ^{76}Ge fraction. The experimental sensitivity can be improved by analyzing the pulse shape of the detector signals with the aim to reject background events. This paper documents the algorithms developed before the data of Phase I were unblinded. The double escape peak (DEP) and Compton edge events of 2.615 MeV \gamma\ rays from ^{208}Tl decays as well as 2\nu\beta\beta\ decays of ^{76}Ge are used as proxies for 0\nu\beta\beta\ decay. For BEGe detectors the chosen selection is based on a single pulse shape parameter. It accepts 0.92$\pm$0.02 of signal-like events while about 80% of the background events at Q_{\beta\beta}=2039 keV are rejected.
For semi-coaxial detectors three analyses are developed. The one based on an artificial neural network is used for the search of 0\nu\beta\beta\ decay. It retains 90% of DEP events and rejects about half of the events around Q_{\beta\beta}. The 2\nu\beta\beta\ events have an efficiency of 0.85\pm0.02 and the one for 0\nu\beta\beta\ decays is estimated to be 0.90^{+0.05}_{-0.09}. A second analysis uses a likelihood approach trained on Compton edge events. The third approach uses two pulse shape parameters. The latter two methods confirm the classification of the neural network since about 90% of the data events rejected by the neural network are also removed by both of them. In general, the selection efficiency extracted from DEP events agrees well with those determined from Compton edge events or from 2\nu\beta\beta\ decays.

M Agostini et al., (GERDA Collaboration), N. Frodyma, K. Pelczar, M. Wojcik, G. Zuzel

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http://arxiv.org/abs/1306.5084

http://link.springer.com/article/10.1140/epjc/s10052-014-2764-z

Abstract

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.

Applied Radiation and Isotopes 81 (2013) 146–150

M. Misiaszek a), K. Pelczar a), M. Wójcik a), G. Zuzel a) & M. Laubenstein b)

a) M. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, PL-30-059 Kraków, Poland
b) Laboratori Nazionali del Gran Sasso, INFN, S.S. 17/bis km 18+910, Assergi(AQ), I-67100 Italy

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http://dx.doi.org/10.1016/j.apradiso.2013.03.006

Abstract

Results of alpha spectrometric measurements deep underground and above ground with and without active veto show that the underground measurement of thick samples is the most sensitive method due to significant reduction of the muon-induced background. In addition, the polonium diffusion for some samples requires an appropriate selection of an energy region in the registered spectrum. On the basis of computer simulations the best counting conditions are selected for a thick lead sample in order to optimize the detection limit.

Mikael Hult a), Guillaume Lutter a), Ayhan Yüksela b), Gerd Marissens a), Marcin Misiaszek c), Ulf Rosengard a)

a) European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), Retieseweg 111, B-2440 Geel, Belgium
b) TAEK-CNAEM, Turkish Atomic Energy Authority, Istanbul, Turkey
c) Smoluchowski Institute of Physics, Jagiellonian University, ul. Reymonta 4, PL-30-059 Krakow, Poland

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http://dx.doi.org/10.1016/j.apradiso.2013.03.081

Abstract

In underground HPGe-detector systems where the cosmic ray induced background is low, it is often difficult to assess the location of background sources. In this study, background counting rate of different HPGe-detectors in different lead shields is reported with the aim of better understanding background sources. To further enhance the understanding of the variations of environmental parameters, the background as a function of time over a long period was also studied.

Applied Radiation and Isotopes 81 (2013) 81–86

Guillaume Lutter a), Mikael Hult a), Gerd Marissens a), Erica Andreotti a), Ulf Rosengård a), Marcin Misiaszek b), Ayhan Yüksela c) & Namik Sahina d)

a) European Commission, DG JRC, Institute for Reference Materials and Measurements (IRMM), Retieseweg 111, 2440 Geel, Belgium
b) Smoluchowski Institute of Physics, Jagiellonian University, ul. Reymonta 4, PL-30-059 Krakow, Poland
c) TAEK-CNAEM, Turkish Atomic Energy Authority, Istanbul, Turkey
d) TAEK-SANAEM, Turkish Atomic Energy Authority, Ankara,Turkey

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http://dx.doi.org/10.1016/j.apradiso.2013.03.079

Abstract

The newest development in IRMM’s underground analytical facility is a large lead shield lined with copper that is versatile and can host several detectors of different types. The characteristics and the background performance of the shield are described for four different detector configurations involving HPGe-detectors and NaI-detectors. The shield has been designed to swap detectors, while still maintaining a low background. This enables testing of detectors for other experiments and optimisation of detection limits for specific radionuclides in different projects.

²²⁶Ra, ²¹⁰Pb, ²¹⁰Bi and ²¹⁰Po deposition and removal from surfaces and liquids

M. Wójcik and G. Zuzel

Download: DOI: 10.1007/s10967-012-2180-5

Abstract

Deposition of 226Ra from water on nylon was investigated. Measurements performed for different pH and different radium concentrations in the water gave similar absolute activities deposited on the foil surface. Obtained results were used to estimate the amount of 226Ra plated-out on the nylon scintillator vessel in the solar neutrino experiment BOREXINO during filling of the detector. Another problem studied in the frame of BOREXINO was the removal of 210Pb from its organic liquid scintillator by applying distillation and water extraction. After several tests had been performed for both methods it was found that after the water extraction the initial lead content in the scintillator sample was reduced only accordingly to the ratio of the volumes of the applied liquids (simple dilution). In contrast to this, distillation was very effective providing in the best case a 210Pb reduction factor higher than 100. Removal efficiencies of the long-lived 222Rn daughters during etching from surfaces of standard and high purity germanium were investigated in the frame of the GERDA experiment, which aims to search for neutrino-less double beta decay of 76Ge. The standard etching procedure of Canberra used during production of high purity n-type germanium diodes was applied to germanium discs, which had been exposed earlier to a strong 222Rn source for its progenies deposition. In contrast to copper and stainless steel, 210Pb, 210Bi and 210Po was removed from germanium very efficiently. An evidence of a reverse process was also observed—the isotopes were transferred from the etchant to the clean germanium surface.