[en] The progress in the development of the GERDA (GErmanium Detector Array) experiment is presented. The goal of the experiment is the search for neutrinoless double beta decay of ⁷⁶Ge with considerable reduction of background in comparison with predecessor experiments. GERDA will operate bare germanium semiconductor detectors (enriched in ⁷⁶Ge) submerged in high purity liquid argon supplemented by a water shield. The experimental set up is currently under construction in the underground facility of LNGS, Italy. The results of various R and D efforts and the main steps of the GERDA set up design and installation are given as well as several novel methods for background reduction are described.

[en] The next generation DBD-experiment GERDA will operate HP-Ge-diodes in liquid argon (LAr). LAr scintillates at a wavelength of 128 nm. LArGe(Liquid ARgon GErmanium) is a R and D project, researching the properties of the scintillation and its use as anti-coincidence signal for the HP-Ge detectors operated in the LAr. The scintillation light is shifted by a wavelength-shifter (WLS) and detected by a cryogenic photo-multiplier-tube (PMT) immersed in the LAr. By optimization of the WLS the photo-electron yield has been improved from 400 pe/MeV to 1100 pe/MeV and has been stable for more than 6 months. LAr scintillation light is emitted from two different excited molecular states, a singlet and a triplet state. The decay time constants are 6 ns for the singlet and 1.6 s for the triplet state and the population of the states depends on the ionization density of the incident particle. This allows for a powerful discrimination between particles of different ionization densities, i.e. between gammas, alphas and neutrons. The addition of Xe to the LAr can increase the light yield and has a significant impact on the pulse shape. First results from this ongoing research are presented. (orig.)

[en] The response of a 19 kg active mass liquid argon scintillation detector to gamma, alpha and neutron radiation and its characteristic scintillation photon time distribution has been studied in the framework of the Gerda double beta decay research and development program. The achieved photo-electron yield of 1.24 pe/keV was stable during the two years of operation. The detector exhibits excellent energy resolution of 8.7/17.2 keV (σ) for gamma energies of 60/239 keV. Radon was loaded into the liquid argon to study alpha energy quenching and decay time correlation of its progenies. A robust pulse shape analysis method was used to identify and discriminate amongst the different radiation types. 60 keV gamma signals could be discriminated against neutron recoils of the same visible energy with a miss-identification probability of < 5 · 10^-4 limited by statistics and ambient backgrounds. Xenon doping of liquid argon increased the photo-electron yield and improved the spectroscopic performance of the detector leading to an energy resolution of 7.2/15.4 keV (σ) for 60/239 keV. The discrimination power improved slightly with the addition of xenon up to concentrations of 300 ppm. Applications for background identification and discrimination in double beta decay search with ⁷⁶Ge crystals, as well as for Dark Matter search with liquid argon are discussed

[en] The positive effect in the experiment to search for two-neutrino ββ decay of ¹⁵⁰Nd by using Time Projection Chamber is obtained. The ¹⁵⁰Nd half-life is defined from the analysis of the data accumulated with a sample of ¹⁵⁰Nd (92% enrichment) and a sample with the natural isotopic composition ^natNd. The value of half-life is 1.7x10¹⁹ yr, and the effect to the background ratio is 4/1. (author). 8 refs., 3 figs

[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] The ^63,65Cu NMR and NQR spectra have been obtained in single crystal sample of CuCrO₂ in the magnetically ordered phase. The components of the electric field gradient tensor (EFG) characterizing the structure of the nearest environment of copper ions are determined from the analysis of the spectra. Comparative analysis obtained data with similar data of paramagnetic phase showed that the local charge environment of copper nuclei does not change during the magnetic phase transition. (paper)

[en] The International Germanium Experiment (IGEX) operated with 3 detectors of approximately 700 gm fiducial mass and 3 detectors of approximately 2 kg fiducial mass each. They were fabricated from germanium isotopically enriched to 86% in 76Ge. The total fiducial mass was 8.4 kg. They were mounted in ultra-low radioactive background cryostats electroformed from purified CuSO4 solution

[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] The GERDA (GERmanium Detector Array) experiment, located in the Gran Sasso Underground Laboratory (LNGS, Italy) aims to search for neutrinoless double beta (0νββ) decay of the "7"6Ge isotope. Both an ultra-low radioactivity background environment and active techniques to abate the residual background are required to reach the background index (of 10"−"3 counts/keV kg y) at the Q_β_β. In order to veto and suppress those events that partially deposit energy in Ge detectors, the readout of liquid argon (LAr) scintillation light (SL) has been implemented for the second GERDA experimental Phase. A double veto system has been designed and constructed using highly radiopure materials (scintillating fibers, wavelength shifters, polymeric foils, reflective foils). This work describes the study of lead, thorium and uranium ultra-trace content, performed at the LNGS Chemistry Laboratory by High Resolution Mass Spectrometry (HR ICP MS), for the selection of all materials involved in the construction of the veto system