[en] Background estimations in neutrinoless double beta decay experiments (0νββ) require reliable statistical limits on gamma-spectrometric low-level material screening measurements. For this purpose a custom method based on Bayesian statistics with reference to the international standard ISO 11929-7 is presented. The analysis combines the data from sample- and background spectra and comprises the physical knowledge of non-negative counting rates. It allows to incorporate multiple gamma lines of radionuclides. The confidence intervals pass continuously from two-sided intervals into single-sided upper limits.

No abstract available

[en] An optimisation of the geometrical model of a p-type detector used for material screening was carried out to improve the accuracy of Monte Carlo simulations in reproducing spectrometric measurements. Gamma-ray sources were measured to determine the dimensions of the detector dead layer and borehole. An agreement between simulations and measurement within 3% was achieved at energies above 100 keV. In contrast, discrepancies on the order of 23% were encountered using the nominal parameters from the detector manufacturer.

[en] 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 m³, 1.4tons), which in addition is instrumented with photomultipliers to detect argon scintillation light. The light is 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 10³ have been achieved. First background data of LArGe with a coaxial HPGe detector (without PSD) yield a background index of the order 10⁻² cts/(keV-kg-y), which is at the level of the GERDA phase I design goal. As a consequence of these results, the development of an active liquid argon veto in GERDA is pursued.

[en] In low-level gamma spectrometry, one of the main goals is the improvement of detection sensitivity. However, ensuring the accuracy and compatibility of the measurement results in different laboratories is also very important. This has been particularly highlighted within the GERDA collaboration, which incorporates several low-level material screening laboratories. For this reason a comparison of gamma-spectrometers situated at MPIK Heidelberg, IRMM Geel, LNGS Assergi and JINR Dubna was performed. This comparison was based on the National Physical Laboratory's ''Environmental Radioactivity Comparison 2005'' exercise, in which MPIK Heidelberg and IRMM Geel participated. The exercise allowed comparing the accuracy of the measurements and the different evaluation techniques between many low-level laboratories, using the same standard mixture of low-radioactivity nuclides. The results of the internal comparison are presented and discussed, as well as the implementation of the Monte-Carlo simulations in the evaluation of our measurements. (orig.)

[en] In low-level gamma spectrometry, one of the main goals is the improvement of detection sensitivity. However, ensuring the accuracy and compatibility of the measurement results in different laboratories is also very important. This has been particularly highlighted within the GERDA collaboration, which incorporates several low-level material screening laboratories. For this reason a comparison of gamma-spectrometers situated at MPIK Heidelberg, IRMM Geel, LNGS Assergi and JINR Dubna was performed. This comparison was based on the National Physical Laboratory's 'Environmental Radioactivity Comparison 2005' exercise, in which MPIK Heidelberg and IRMM Geel participated. The exercise allowed comparing the accuracy of the measurements and the different evaluation techniques between many low-level laboratories, using the same standard mixture of low-radioactivity nuclides. The results of the internal comparison are presented and discussed, as well as the implementation of the Monte-Carlo simulations in the evaluation of our measurements

[en] 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, 1.4tons), 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) x 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 "4"2Ar abundance (parallel to GERDA), and have indication for the 2νββ-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. (orig.)

[en] Background coming from the ⁴²Ar decay chain is considered to be one of the most relevant for the Gerda experiment, which searches for the neutrinoless double beta decay of ⁷⁶Ge. The sensitivity strongly relies on the absence of background around the Q-value of the decay. Background coming from ⁴²K, a progeny of ⁴²Ar, can contribute to that background via electrons from the continuous spectrum with an endpoint at 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 ⁴²K 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 ⁴²K background by three orders of magnitude. This is sufficient for Phase II of the Gerda experiment. (orig.)

[en] In present and future experiments in the field of rare events physics a background index of 10^-3 counts/(keV kg a) or better in the region of interest is envisaged. A thorough material screening is mandatory in order to achieve this goal. The results of a systematic study of radioactive trace impurities in selected materials using ultra low-level gamma-ray spectrometry in the framework of the GERDA experiment are reported.

[en] 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 the experiment 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. (orig.)