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A discovery that neutrinos are Majorana fermions would have profound implications for particle physics and cosmology. The Majorana character of neutrinos would make possible the neutrinoless double-β (0νββ) decay, a matter-creating process without the balancing emission of antimatter. The GERDA Collaboration searches for the 0νββ decay of 76Ge by operating bare germanium detectors in an active liquid argon shield. With a total exposure of 82.4 kg·year, we observe no signal and derive a lower half-life limit of T 1/2 > 0.9 × 1026 years (90% C.L.). Our T 1/2 sensitivity, assuming no signal, is 1.1 × 1026 years. Combining the latter with those from other 0νββ decay searches yields a sensitivity to the effective Majorana neutrino mass of 0.07 to 0.16 electron volts.

The Gerda collaboration is performing a sensitive search for neutrinoless double beta decay of 76Ge at the INFN Laboratori Nazionali del Gran Sasso, Italy. The upgrade of the Gerda experiment from Phase I to Phase II has been concluded in December 2015. The first Phase II data release shows that the goal to suppress the background by one order of magnitude compared to Phase I has been achieved. Gerda is thus the first experiment that will remain “background-free” up to its design exposure (100 kgyear). It will reach thereby a half-life sensitivity of more than 1026 year within 3 years of data collection. This paper describes in detail the modifications and improvements of the experimental setup for Phase II and discusses the performance of individual detector components.

This study presents original data on the content of radionuclides of natural (primordial and cosmogenic) and man-made origin in the assimilation apparatus of Scots pine ( Pinus sylvestris L.), which grows in the Western Caucasus (within the Karachay-Cherkess Republic). The contents of radioisotopes of beryllium ( 7 Be), potassium ( 40 K), thorium ( 232 Th), uranium ( 238 U) and cesium ( 137 Cs) were detected in the pine needles. Close correlation with the height of the growing site of 7 Be, 238 U, and 137 Cs contents in pine needle samples was identified.

Method of measurement and result of processing of the Po -active isotope half-life data measured in long-run continuous measurement with the underground low-background TAU-3 set-up are described. The set-up consists of two scintillation NaI(Tl) mm detectors and double-layer ( mm) plastic scintillator detector (PCD) with mm. Source of the … decays was placed between the PSD layers. The half-life was calculated from a decay curve. The curve was constructed from delay values between - and -pulses detected by the PSD. Two methods were used for the event selection. The PSD pulses coincided in 16 mcs time window were selected in the first case (double coincidences). Additional pulse of the NaI detected -quantum from the Bi decay was used in the second case for a validation of the Po birth and decay (triple coincidences). The values mcs for the double coincidences and mcs for the triple coincidences were obtained for Po half-life. Possible reasons of the result difference are discussed.

The GERmanium Detector Array (Gerda) is a low background experiment located at the Laboratori Nazionali del Gran Sasso in Italy, which searches for neutrinoless double-beta decay of \\[^{76}\\]Ge into \\[^{76}\\]Se+2e\\[^-\\]. Gerda has been conceived in two phases. Phase II, which started in December 2015, features several novelties including 30 new 76Ge enriched detectors. These were manufactured according to the Broad Energy Germanium (BEGe) detector design that has a better background discrimination capability and energy resolution compared to formerly widely-used types. Prior to their installation, the new BEGe detectors were mounted in vacuum cryostats and characterized in detail in the Hades underground laboratory in Belgium. This paper describes the properties and the overall performance of these detectors during operation in vacuum. The characterization campaign provided not only direct input for Gerda Phase II data collection and analyses, but also allowed to study detector phenomena, detector correlations as well as to test the accuracy of pulse shape simulation codes.

The beta decay of 77 Ge and 77 m Ge, both produced by neutron capture on 76 Ge, is a potential background for Germanium based neutrinoless double-beta decay search experiments such as GERDA or the LEGEND experiment. In this work we present a search for 77 Ge decays in the full GERDA Phase II data set. A delayed coincidence method was employed to identify the decay of 77 Ge via the isomeric state of 77 As ( 9 / 2 + , 475 keV , T 1 / 2 = 114 μ s , 77 m As). New digital signal processing methods were employed to select and analyze pile-up signals. No signal was observed, and an upper limit on the production rate of 77 Ge was set at < 0.216 nuc/(kg · yr) (90% CL). This corresponds to a total production rate of 77 Ge and 77 m Ge of < 0.38 nuc/(kg ·  yr) (90% CL), assuming equal production rates. A previous Monte Carlo study predicted a value for in-situ 77 Ge and 77 m Ge production of (0.21 ± 0.07) nuc/(kg.yr), a prediction that is now further corroborated by our experimental limit. Moreover, tagging the isomeric state of 77 m As can be utilised to further suppress the 77 Ge background. Considering the similar experimental configurations of LEGEND-1000 and GERDA, the cosmogenic background in LEGEND-1000 at LNGS is estimated to remain at a sub-dominant level.

The Gerda experiment located at the Laboratori Nazionali del Gran Sasso of INFN searches for neutrinoless double beta (0 νββ ) 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 γ rays from 208 Tl decays as well as two-neutrino double beta (2 νββ ) decays of 76 Ge are used as proxies for 0 νββ decay. For BEGe detectors the chosen selection is based on a single pulse shape parameter. It accepts 0.92±0.02 of signal-like events while about 80 % of the background events at Q ββ =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 νββ decay. It retains 90 % of DEP events and rejects about half of the events around Q ββ . The 2 νββ events have an efficiency of 0.85±0.02 and the one for 0 νββ decays is estimated to be . 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 νββ decays.

The radioactive isotope 85 Kr is found in significant quantities in the atmosphere largely due to nuclear industry. Its β -decay with a half-life of 10.7 years and a Q-value of 687 keV is a dangerous background source for low-threshold noble gas and liquid detectors, which distill their detector medium from air. The Gerda experiment was operating high-purity germanium detectors immersed in a clean liquid argon bath deep underground to search for neutrinoless double beta decay with unprecedented sensitivity. The 85 Kr specific activity in the liquid argon at the start of the second phase of the experiment has been determined to be ( 0.36 ± 0.03 )  mBq/kg through an analysis of the full subsequent data set that exploits the excellent γ -ray spectroscopic capabilities of Gerda .

—The article presents the results of measuring 222 Rn activity and its daughter decay products in the air of underground laboratories of Baksan Neutrino Observatory, Institute for Nuclear Research, Russian Academy of Sciences (BNO INR RAS) at different distances from the entrance. The measurements were carried out with a cylindrical air pulse ionization chamber. It has been shown that the radon content in the flow of ventilated air, within the measurement accuracy, does not depend on the length of the path traveled, but increases abruptly in the locations of sources of underground gas and water emissions. Various mechanisms of air enrichment with radon are considered. The research methodology is presented, and the results of measurements of radon emission from the rocky soil of the walls of an underground room are presented. The results of measuring the radon content in water from various above- and underground sources using a low-background gamma spectrometer based on a semiconductor detector (SCD) made of ultrapure germanium are presented.

Results of a search for the masked regularities in the Po -active isotope half-life solar-daily variation parameters in the data collected during 2012–2015 years are presented. It is shown, that an amplitude of a sinusoidal function approximating half-life solar-daily dependence obtained by averaging data during 90 days for each season of the years could reach from the average daily value. Similar analysis of the Po data collected in 2018–2022 years shows that amplitude of the deviation from the average value could reach . This effect limits an accuracy of the high precision measurements with this or similar short-lived isotopes generating systematic errors if the data were collected during a relatively short time. The new value of the Po half-life which is Po s was obtained on the base of the data collected during 2018–2022 years.