[en] The results of the HEIDELBERG-MOSCOW experiment which searches with 11 kg of enriched ⁷⁶Ge for double beta decay in the Gran Sasso underground laboratory are presented for the full running period August 1990-May 2003. The duty cycle of the experiment was ∼80%, the collected statistics is 71.7 kg yr. The background achieved in the energy region of the Q value for double beta decay is 0.11 events kg^-1 yr^-1 keV^-1. The two-neutrino accompanied half-life is determined on the basis of more than 100 000 events. The confidence level for the neutrinoless signal has been improved to 4.2σ

[en] Data acquisition in a long-running underground experiment has its specific experimental challenges, concerning data acquisition, stability of the experiment and background reduction. These problems are addressed here for the HEIDELBERG-MOSCOW experiment, which collected data in the period August 1990-May 2003. The measurement and the analysis of the data are presented. The duty cycle of the experiment was ∼80%, and the collected statistics is 71.7 kg year. The background achieved in the energy region of the Q value for double beta decay is 0.11 events/kg year keV. The two-neutrino accompanied half-life is determined on the basis of more than 100 000 events. The confidence level for the neutrinoless signal has been improved to a 4σ level

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[en] GENIUS-TF (Nucl. Instr. and Meth. A 511 (2003) 341; Nucl. Instr. and Meth. A 481 (2002) 149.) is a test-facility for the GENIUS project (GENIUS-Proposal, 20 November 1997; Z. Phys. A 359 (1997) 351; CERN Courier, November 1997, 16; J. Phys. G 24 (1998) 483; Z. Phys. A 359 (1997) 361; in: H.V. Klapdor-Kleingrothaus, H. Pas. (Eds.), First International Conference on Particle Physics Beyond the Standard Model, Castle Ringberg, Germany, 8-14 June 1997, IOP Bristol (1998) 485 and in Int. J. Mod. Phys. A 13 (1998) 3953; in: H.V. Klapdor-Kleingrothaus, I.V. Krivosheina (Eds.), Proceedings of the Second International Conference on Particle Physics Beyond the Standard Model BEYOND' 99, Castle Ringberg, Germany 6-12 June 1999, IOP Bristol (2000) 915), a proposed large scale underground observatory for rare events which is based on operation of naked germanium detectors in liquid nitrogen for an extreme background reduction. Operation of naked Ge crystals in liquid nitrogen has been applied routinely already for more than 20 years by the CANBERRA Company for technical functions tests (CANBERRA Company, private communication, 5 March 2004.), but it never had found entrance into basic research. Only in 1997 first tests of application of this method for nuclear spectroscopy have been performed, successfully, in Heidelberg (Klapdor-Kleingrothaus et al., 1997, 1998; J. Hellmig and H.V. Klapdor-Kleingrothaus, 1997). On May 5, 2003 the first four naked high-purity germanium detectors (total mass 10.52 kg) were installed in liquid nitrogen in the GENIUS Test Facility at the Gran Sasso underground laboratory. Since then the experiment has been running continuously, testing for the first time the novel technique in an underground laboratory and for a long-lasting period. In this work, we present the first analysis of the GENIUS-TF background after the completion of the external shielding, which took place in December 2003. We focus especially on the background coming from ²²²Rn daughters. This is found to be at present by a factor of 200 higher than expected from simulation. It is still compatible with the scientific goal of GENIUS-TF, namely to search for cold dark matter by the modulation signal, but on the present level would cause serious problems for a full GENIUS--like experiment using liquid nitrogen

[en] In this work, we present the results obtained measuring the ²¹⁴Bi spectrum from a ²²⁶Ra source with a high-purity germanium detector. Our attention was mostly focused on the energy region around the Q-value of ⁷⁶Ge neutrinoless double-beta decay (2039.006 keV). The results of this measurement are strongly related to the first indication for the neutrinoless double-beta decay of ⁷⁶Ge, given by a recent analysis (Mod. Phys. Lett. A 16 (37) (2001) 2409; Part. Nucl. 110 (2002) 57; Found. Phys. 31 (2002) 1181; in: H.V. Klapdor-Kleingrothaus, R.D. Viollier (Eds.), Proceedings of DARK2002, Cape Town, South Africa, February 4-9, 2002, Springer, Heidelberg, 2002, pp. 367-403) of the data collected during 10 years of measurements from the HEIDELBERG-MOSCOW experiment

[en] The first four naked high-purity Germanium detectors were installed successfully in liquid nitrogen in the GENIUS-Test-Facility in the GRAN SASSO Underground Laboratory on May 5, 2003. This is the first time ever that this novel technique aiming at extreme background reduction in search for rare decays is going to be tested underground. First operational parameters are presented