•A large custom cryogen-free cryostat has been designed and built in order to operate the CUORE detector.•The CUORE cryostat has a 1 m3 experimental volume and is able to host a tonne-scale ...bolometric detector.•The CUORE cryostat guarantees a low noise and low radioactivity environment, needed to search for 0nbb.•The CUORE detector has been cooled down to 8.3 mK and steadily operated at 15 mK, proving the success of the cryostat.
The CUORE experiment is the world’s largest bolometric experiment. The detector consists of an array of 988 TeO2 crystals, for a total mass of 742 kg. CUORE is presently taking data at the Laboratori Nazionali del Gran Sasso, Italy, searching for the neutrinoless double beta decay of 130Te. A large custom cryogen-free cryostat allows reaching and maintaining a base temperature of ∼10 mK, required for the optimal operation of the detector. This apparatus has been designed in order to achieve a low noise environment, with minimal contribution to the radioactive background for the experiment. In this paper, we present an overview of the CUORE cryostat, together with a description of all its sub-systems, focusing on the solutions identified to satisfy the stringent requirements. We briefly illustrate the various phases of the cryostat commissioning and highlight the relevant steps and milestones achieved each time. Finally, we describe the successful cooldown of CUORE.
We construct the first comprehensive radioactive background model for a dark matter search with charge-coupled devices (CCDs). We leverage the well-characterized depth and energy resolution of the ...DAMIC at SNOLAB detector and a detailed geant4-based particle-transport simulation to model both bulk and surface backgrounds from natural radioactivity down to 50 eVee . We fit to the energy and depth distributions of the observed ionization events to differentiate and constrain possible background sources, for example, bulk H 3 from silicon cosmogenic activation and surface Pb210 from radon plate-out. We observe the bulk background rate of the DAMIC at SNOLAB CCDs to be as low as 3.1±0.6 countskg-1day-1 keVee-1 , making it the most sensitive silicon dark matter detector. Finally, we discuss the properties of a statistically significant excess of events over the background model with energies below 200 eVee .
Recent developments of the nuclear emulsion technology led to the production of films with nanometric silver halide grains suitable to track low energy nuclear recoils with submicrometric length. ...This improvement opens the way to a directional Dark Matter detection, thus providing an innovative and complementary approach to the on-going WIMP searches. An important background source for these searches is represented by neutron-induced nuclear recoils that can mimic the WIMP signal. In this paper we provide an estimation of the contribution to this background from the intrinsic radioactive contamination of nuclear emulsions. We also report the neutron-induced background as a function of the read-out threshold, by using a GEANT4 simulation of the nuclear emulsion, showing that it amounts to about 0.06 per year per kilogram, fully compatible with the design of a 10 kg × year exposure.
We describe in detail the methods used to obtain the lower bound on the lifetime of neutrinoless double-beta (0 nu beta beta) decay in Te-130 and the associated limit on the effective Majorana mass ...of the neutrino using the CUORE-0 detector. CUORE-0 is a bolometric detector array located at the Laboratori Nazionali del Gran Sasso that was designed to validate the background reduction techniques developed for CUORE, a next-generation experiment scheduled to come online in 2016. CUORE-0 is also a competitive 0 nu beta beta decay search in its own right and functions as a platform to further develop the analysis tools and procedures to be used in CUORE. These include data collection, event selection and processing, as well as an evaluation of signal efficiency. In particular, we describe the amplitude evaluation, thermal gain stabilization, energy calibration methods, and the analysis event selection used to create our final 0 nu beta beta search spectrum. We define our high level analysis procedures, with emphasis on the new insights gained and challenges encountered. We outline in detail our fitting methods near the hypothesized 0 nu beta beta decay peak and catalog the main sources of systematic uncertainty. Finally, we derive the 0 nu beta beta decay half-life limits previously reported for CUORE-0, T-1/2(0 nu) > 2.7 x 10(24) yr, and in combination with the Cuoricino limit, T-1/2(0 nu) > 4.0 x 10(24) yr.
The main target of this study is the development and the validation of an internal procedure to measure the pg
g
−1 levels, of naturally occurring radioisotopes to select ultra low background ...detector materials. As there are no ultra low-level certified reference materials commercially available, the performance of ICP-MS was compared with the well established ultra low-level γ-spectroscopy. This work shows also the reliability of very quick ICP-MS semi-quantitative analyses of an environmental matrix such as a geological sample treated according to conventional protocols.
The R&D activity performed during the last years proved the potential of ZnSe scintillating bolometers to the search for neutrino-less double beta decay, motivating the realization of the first ...large-mass experiment based on this technology: CUPID-0. The isotopic enrichment in Se-82, the (ZnSe)-Se-82 crystals growth, as well as the light detectors production have been accomplished, and the experiment is now in construction at Laboratori Nazionali del Gran Sasso (Italy). In this paper we present the results obtained testing the first three (ZnSe)-Se-82 crystals operated as scintillating bolometers, and we prove that their performance in terms of energy resolution, background rejection capability and intrinsic radiopurity complies with the requirements of CUPID-0.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present a new analysis of previously published SuperCDMS data using a profile likelihood framework to search for sub-GeV dark matter (DM) particles through two inelastic scattering channels: ...bremsstrahlung radiation and the Migdal effect. By considering these possible inelastic scattering channels, experimental sensitivity can be extended to DM masses that are undetectable through the DM-nucleon elastic scattering channel, given the energy threshold of current experiments. We exclude DM masses down to 220 MeV/c2 at 2.7 x 10-30 cm2 via the bremsstrahlung channel. The Migdal channel search provides overall considerably more stringent limits and excludes DM masses down to 30 MeV/ c2 at 5.0 x 10-30 cm2.
Intrinsic
40
K radioactive backgrounds from impurities of natural K in liquid scintillation cocktails have previously been demonstrated to limit their use in ultra-sensitive applications. This work ...explores two methodologies in parallel for the reduction of
40
K backgrounds in the cocktails, and lays the groundwork for use in ultra-sensitive applications. In one method, alternative low-K liquid scintillation matrix constituents were identified and in the other, a simple purification method for single components and finished cocktails was developed. Both methods were verified via ICP-MS analysis. Liquid scintillation counting of selected purified cocktails demonstrated background reduction, improved stability, and enhanced performance. The best performing purified cocktail was also counted on a custom-built ultra-low background liquid scintillation counter, with results below the detector background.
The performance of LSC cocktails in ultra-sensitive applications was evaluated. Backgrounds from radioactive contaminations in commercially available and in-house developed liquid scintillation ...cocktails were measured and compared to the predicted background levels of the ultra-low background liquid scintillation counter. Through the ICP-MS assay of the cocktails and their constituents, potassium impurities in the surfactant component were identified as a significant source of background, potentially limiting the use of LSC counting in ultra-sensitive applications. This work lays the groundwork for future research towards ultrapure LSC cocktails for ultrasensitive LSC counting.
Dust particulate fallout on materials in use for rare-event searches is a concerning source of radioactive backgrounds due to the presence of the naturally occurring radionuclides 40K, 232Th, 238U, ...and their progeny in dust. Much effort is dedicated to inform radioactive backgrounds from dust and evaluate the efficacy of mitigation procedures. A great portion of such effort relies on fallout models and assumed dust composition. In this work, an ICP-MS based methodology was employed for a direct determination of fallout rates of radionuclides and stable isotopes of interest from dust particulate at the SNOLAB facility. Hosted in an active mine, the SNOLAB underground laboratory strives to maintain experimental areas at class 2000 cleanroom level. This work validates the mitigation procedures in place at SNOLAB and informs dust backgrounds during laboratory activities. Fallout rates of major constituents of the local rock were measured two to three orders of magnitude lower in the clean experimental areas compared to non-clean transition areas from the mine to the laboratory. An increase of approximately two orders of magnitude in the fallout rate of stable Pb isotopes was determined in an experimental area during activities involving handling of Pb bricks. Increased 40K, 232Th, and 238U fallout rates were measured in clean experimental areas during activities generating particulate.
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