Agostini M. et al. (GERDA Collaboration) M. Wójcik, G. Zuzel, K. Pelczar, K. Panas, M. Misiaszek, N. Frodyma, D. Borowicz

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http://iopscience.iop.org/article/10.1088/0954-3899/42/11/115201

Abstract
Two neutrino double beta decay of 76-Ge to excited states of 76-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 76-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 γ 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:

Agostini M. et al. (GERDA Collaboration) M. Wójcik, G. Zuzel, K. Pelczar, K. Panas, M. Misiaszek, N. Frodyma, D. Borowicz

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http://dx.doi.org/10.1140/epjc/s10052-015-3409-6

Abstract

An optimized digital shaping filter has been developed for the Gerda experiment which searches for neutrinoless double beta decay in 76Ge. The Gerda Phase I energy calibration data have been reprocessed and an average improvement of 0.3 keV in energy resolution (FWHM) corresponding to 10 % at the Q value for 0νββ decay in 76Ge is obtained. This is possible thanks to the enhanced low-frequency noise rejection of this Zero Area Cusp (ZAC) signal shaping filter.

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

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http://dx.doi.org/10.1140/epjc/s10052-014-3253-0

Abstract

The GERmanium Detector Array (Gerda) at the Gran Sasso Underground Laboratory (LNGS) searches for the neutrinoless double beta decay (0νββ) of 76Ge. Germanium detectors made of material with an enriched 76Ge fraction act simultaneously as sources and detectors for this decay. During Phase I of theexperiment mainly refurbished semi-coaxial Ge detectors from former experiments were used. For the upcoming Phase II, 30 new 76Ge enriched detectors of broad energy germanium (BEGe)-type were produced. A subgroup of these detectors has already been deployed in Gerda during Phase I. The present paper reviews the complete production chain of these BEGe detectors including isotopic enrichment, purification, crystal growth and diode production. The efforts in optimizing the mass yield and in minimizing the exposure of the 76Ge enriched germanium to cosmic radiation during processing are described. Furthermore, characterization measurements in vacuum cryostats of the first subgroup of seven BEGe detectors and their long-term behavior in liquid argon are discussed. The detector performance fulfills the requirements needed for the physics goals of Gerda Phase II.

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.

Volume 676, 1 June 2012, Pages 140–148

G. Zuzel a), M. Wójcik b)

a) Max Planck Institute for Nuclear Physics, P.O. Box 103 980, D-69029 Heidelberg, Germany
b) M. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, PL-30-059 Kraków, Poland

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http://www.sciencedirect.com/science/article/pii/S0168900211022522

Abstract

Removal of the long-lived 222Rn daughters from copper and stainless steel surfaces was investigated. Etching and electropolishing were applied to discs exposed earlier to a strong radon source for 210Pb, 210Bi and 210Po deposition. Cleaning efficiency for 210Pb was tested with a n-type high purity germanium spectrometer, for 210Bi a beta spectrometer and for 210Po an alpha spectrometer was used. According to the performed measurements electropolishing removes very effectively all the isotopes from copper and stainless steel. Copper etching reduces efficiently lead and bismuth however for polonium the effect is negligible because of its fast re-deposition. For stainless steel, etching is much more effective compared to copper and it also works for 210Po.

Volume 676, 1 June 2012, Pages 149–154

G. Zuzel a), M. Wójcik b), B. Majorovits c), M.O. Lampert d), P. Wendling d)

a) Max Planck Institute for Nuclear Physics, P.O. Box 103 980, D-69029 Heidelberg, Germany
b) M. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, PL-30-059 Kraków, Poland
c) Max-Planck-Institut für Physik, Föhringer Ring 6, 80805 München, Germany
d) Canberra-France, 1 Chemin de la Roseraie, B.P. 311, 67834 Tanneries Cedex, France

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http://www.sciencedirect.com/science/article/pii/S0168900211021929

Abstract

Removal and deposition efficiencies of the long-lived 222Rn daughters during etching from and onto surfaces of standard and high purity germanium were investigated. The standard etching procedure of Canberra–France used during production of high purity n-type germanium diodes was applied to germanium discs, which have been exposed earlier to a strong radon source for deposition of its progenies. An uncontaminated sample was etched in a solution containing 210Pb, 210Bi and 210Po. All isotopes were measured before and after etching with appropriate detectors. In contrast to copper and stainless steel, they were removed from germanium very efficiently. However, the reverse process was also observed. Considerable amounts of radioactive lead, bismuth and polonium isotopes present initially in the artificially polluted etchant were transferred to the clean high purity surface during processing of the sample.

Erica Andreotti,1, Mikael Hult,1, Raquel González de Orduña,1, Gerd Marissens,1, J. S. Elisabeth Wieslander,1, and Marcin Misiaszek,2

¹EC-JRC-IRMM, Institute for Reference Materials and Measurements, Retieseweg 111, B-2440 Geel, Belgium
²M. Smoluchowski Institute of Physics, Jagiellonian University, ulica Reymonta 4, PL-30-059 Krakow, Poland

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Abstract

The half-life of the rare β⁻ decay of ¹¹⁵In (9/2+) to ¹¹⁵Sn (3/2+) was determined by measuring the subsequent 497.334(22) keV γ-ray emission in a high-purity indium sample. The measurements were carried out by means of ultralow-level γ-ray spectrometry in the HADES underground laboratory, using three different high-purity germanium detectors. The value of the partial half-life for this low-Q_β⁻ transition was measured to be 4.3(5) × 10²⁰ yr.

Raquel González de Orduña, Mikael Hult, Erica Andreotti, Dušan Budjáš, Stefan Schönert and Marcin Misiaszek

Download: http://www.springerlink.com/content/nukj810n451m4115/

Abstract

A simple technique for pulse shape discrimination in HPGe-detectors of the so-called BEGe type, based on just one parameter obtained from one signal read out, is presented here. This technique allows discriminating between pulses generated when the deposited energy is located within a small region of about 1 mm³ from the pulses generated when the energy is deposited at different locations several mm or cm apart. Two possible applications using this technique are: (i) experiments that look for neutrinoless double β decay in ⁷⁶Ge, such as GERDA; (ii) γ spectrometry measurements where the Compton continuum can be reduced and the efficiency for cascading γ-rays can remain high. With this active background reduction technique a Compton suppression factor of about 3 was obtained. The detector response may be influenced by the detector size. The detector used for this study had a diameter of 6 cm, a thickness of 2.6 cm and a relative efficiency of 19%. The results obtained with this detector were consistent with the results obtained by Budjáš et al. [J Instrum 4:10, 2009] with a 50% relative efficiency BEGe detector.

Mikael Hult a, J.S. Elisabeth Wieslander a, c, Gerd Marissens a, Joël Gasparro a, Uwe Wätjen a and Marcin Misiaszek b

a) European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg 111, B-2440 Geel, Belgium
b) M. Smoluchowski Institute of Physics, Jagiellonian University, ul. Reymona 4, 30-059 Krakow, Poland
c) Department of Physics, P.O. Box 35 (YFL), FIN-40014 University of Jyväskylä, Finland

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Abstract

The radioactivity of 180mTa has never been detected. The present attempt to detect it was carried out using a newly developed HPGe sandwich spectrometer installed 500 m water equivalent underground in the HADES laboratory. The sample consisted of 6 discs of tantalum of natural isotopic composition with a total mass of 1500 g and a total mass for 180Ta of 180 mg. The sample was measured for 68 days and the resulting lower bound for the half-life of 180mTa was 2.0×1016 y, which is a factor of 2.8 higher than the previous highest value