Precise radon measurements are a requirement for various applications, ranging from radiation protection over environmental studies to material screening campaigns for rare-event searches. All of them ultimately depend on the availability of calibration sources with a known and stable radon emanation rate. A new approach to produce clean and dry radon sources by implantation of $^{226}$Ra ions into stainless steel has been investigated. In a proof of principle study, two stainless steel plates have been implanted in collaboration with the ISOLDE facility located at CERN. We present results from a complete characterization of the sources. Each sample provides a radon emanation rate of about 2 Bq, which has been measured using electrostatic radon monitors as well as miniaturized proportional counters. Additional measurements using HPGe and alpha spectrometry as well as measurements of the radon emanation rate at low temperatures were carried out.

Low-background liquid xenon detectors are utilized in the investigation of rare events, including dark matter and neutrinoless double beta decay. For their calibration, gaseous 220 Rn can be used. After being introduced into the xenon, its progeny isotope 212 Pb induces homogeneously distributed, low-energy (<30 keV) electronic recoil interactions. We report on the characterization of such a source for use in the XENONnT experiment. It consists of four commercially available 228 Th sources with an activity of 55 kBq. These sources provide a high 220 Rn emanation rate of about 8 kBq. We find no indication for the release of the long-lived 228 Th above 1.7 mBq. Though an unexpected 222 Rn emanation rate of about 3.6 mBq is observed, this source is still in line with the requirements for the XENONnT experiment.

The radium isotopes 226Ra and 228Ra can provide important data on the dynamics of deep-sea hydrothermal plumes that travel the oceans for decades and have great impact on the ocean chemistry. This study focuses on parameters important for obtaining low detection limits for 228Ra using gamma-ray spectrometry. It is present at mBq-levels in samples collected during the US GEOTRACES 2013 cruise to the Southeast Pacific Ocean.

Geo-neutrinos, electron anti-neutrinos produced in beta-decays of naturally occurring radioactive isotopes in the Earth, are a unique direct probe of our planet's interior. After a brief introduction of the geo-neutrinos' properties and of the main aims of their study, we discuss the features of a detector which has recently provided breakthrough achievements in the field, Borexino, a massive, calorimetric liquid scintillator detector installed at the underground Gran Sasso Laboratory. With its unprecedented radiopurity levels achieved in the core of the detection medium, it is the only experiment in operation able to study in real time solar neutrino interactions in the challenging sub-MeV energy region. Its superior technical properties allowed Borexino also to provide a clean detection of terrestrial neutrinos. Therefore, the description of the characteristics of the detected geo-neutrino signal and of the corresponding geological implications are the main core of the discussion contained in this work.

DARk matter WImp search with liquid xenoN (DARWIN1) will be an experiment for the direct detection of dark matter using a multi-ton liquid xenon time projection chamber at its core. Its primary goal will be to explore the experimentally accessible parameter space for Weakly Interacting Massive Particles (WIMPs) in a wide mass-range, until neutrino interactions with the target become an irreducible background. The prompt scintillation light and the charge signals induced by particle interactions in the xenon will be observed by VUV sensitive, ultra-low background photosensors. Besides its excellent sensitivity to WIMPs above a mass of 5GeV/c2, such a detector with its large mass, low-energy threshold and ultra-low background level will also be sensitive to other rare interactions. It will search for solar axions, galactic axion-like particles and the neutrinoless double-beta decay of 136Xe, as well as measure the low-energy solar neutrino flux with <1% precision, observe coherent neutrino-nucleus interactions, and detect galactic supernovae. We present the concept of the DARWIN detector and discuss its physics reach, the main sources of backgrounds and the ongoing detector design and R&D efforts.

After the accident in the Japanese Fukushima Dai-ichi nuclear power plant in March 2011 large amounts of radioactivity were released and distributed in the atmosphere. Among them were also radioactive noble gas isotopes which can be used as tracers to test global atmospheric circulation models. This work presents unique measurements of the radionuclide (133)Xe from Fukushima in the upper troposphere above Germany. The measurements involve air sampling in a research jet aircraft followed by chromatographic xenon extraction and ultra-low background gas counting with miniaturized proportional counters. With this technique a detection limit of the order of 100 (133)Xe atoms in liter-scale air samples (corresponding to about 100 mBq/m(3)) is achievable. Our results provide proof that the (133)Xe-rich ground level air layer from Fukushima was lifted up to the tropopause and distributed hemispherically. Moreover, comparisons with ground level air measurements indicate that the arrival of the radioactive plume at high altitude over Germany occurred several days before the ground level plume.

We have developed a new method to measure krypton traces in xenon at unprecedented low concentrations. This is a mandatory task for many near-future low-background particle physics detectors. Our system separates krypton from xenon using cryogenic gas chromatography. The amount of krypton is then quantified using a mass spectrometer. We demonstrate that the system has achieved a detection limit of 8 ppq (parts per quadrillion) and present results of distilled xenon with krypton concentrations below 1 ppt.

BOREXINO has set new standards in the field of ultra-low background experiments. Such a success was only possible by a strict quality control program during the construction phase of the experiment. In this paper, we describe how construction materials and auxiliary systems of the BOREXINO detector were screened for their residual radioactivity with unprecedented high sensitivity. The highly sensitive assay techniques developed for this purpose were also used to validate the purity of water and nitrogen used in the experiment. Moreover, we report on the production of 222 Rn -free nitrogen and synthetic air with very low 222 Rn concentration as well as on the successful search for commercial nitrogen with a particularly low concentration of argon and krypton.

Radon is a source of background in many astroparticle physics experiments searching for rare low energy events. In this paper an overview about radon in the field is given including radon detection techniques, radon sources and material screening with respect to radon emanation. Finally, also the problem of long-lived radioactive Rn-222-daughters and the question of gas purification from radon is addressed.

BOREXINO is a large organic liquid scintillation experiment located in the Italian Gran Sasso underground laboratory. The extremely high radio-purity of the interior of the detector allows the real-time detection of rare neutrino fluxes at low energies. For the solar 7Be-neutrino flux an event rate of (49± 3stat ± 4syst ) counts/(d·100 t) was found. The 8B-flux could be measured with the lowest ever achieved threshold of 3 MeV. The result is (0.22± 0.04stat ± 0.01syst ) counts/(d·100 t). BOREXINO has also detected anti-neutrino from European nuclear reactors and from the earth. For geo neutrinos a clear observation with 4.2 σ evidence was accomplished. The experiment is now preparing for precision measurements and for the detection of yet unobserved lower intensity neutrino fluxes.

The behaviour of radon in a cryogenic environment is still not well known. Therefore, measured radon emanation rates at room temperature cannot be translated directly to cryogenic conditions. In this work we present a table‐top experiment that provides a direct way of determining the behaviour of 222Rn in cryogenic argon and helium at liquid argon temperature. We observe an increased emanation rate of 222Rn atoms to liquid argon compared to the rate observed to helium at room temperature. We also find that 222Rn atoms stick to cold metal surfaces when emanated to helium at liquid argon temperature but partly distribute in the liquid when emanated to cryogenic argon. Concluding, we give possible interpretations of the observations.

The GERDA experiment operates bare Germanium diodes enriched in 76Ge in an environment of pure liquid argon to search for neutrinoless double beta decay. A very low radioactive background is essential for the success of the experiment. We present here the research done in order to remove radio‐impurities coming from the liquid argon, the stainless steel cryostat and the front‐end electronics. We found that liquid argon can be purified efficiently from 222Rn. The main source of 222Rn in GERDA is the cryostat which emanates about 55 mBq. A thin copper shroud in the center of the cryostat was implemented to prevent radon from approaching the diodes. Gamma ray screening of radio‐pure components for front‐end electronics resulted in the development of a pre‐amplifier with a total activity of less than 1 mBq 228Th.

Aerosol samples collected on filter media were analyzed using HPGe detectors employing varying background-reduction techniques in order to experimentally evaluate the opportunity to apply ultra-low background measurement methods to samples collected, for instance, by the Comprehensive Test Ban Treaty International Monitoring System (IMS). In this way, realistic estimates of the impact of low-background methodology on the sensitivity obtained in systems such as the IMS were assessed. The current detectability requirement of stations in the IMS is 30 μBq/m3 of air for 140Ba, which would imply ~106 fissions per daily sample. Importantly, this is for a fresh aerosol filter. One week of decay reduces the intrinsic background from radon daughters in the sample allowing much higher sensitivity measurement of relevant isotopes, including 131I. An experiment was conducted in which decayed filter samples were measured at a variety of underground locations using Ultra-Low Background (ULB) gamma spectroscopy technology. The impacts of the decay and ULB are discussed.