Techniques allowing investigation and reduction of backgrounds are crucial for all experiments looking for rare events. In this paper investigations of 222Rn, germanium spectroscopy and noble gas ...mass spectrometry will be described. Selected measurements and their applications in the Borexino and GERDA experiments will be 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
Ge into
Se+2e
. ...Gerda has been conceived in two phases. Phase II, which started in December 2015, features several novelties including 30 new
Ge 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.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Results of alpha spectrometric measurements performed deep underground and above ground with and without active veto show that the underground measurement of thick samples is the most sensitive ...method due to significant reduction of the muon-induced background. In addition, the polonium diffusion requires for some samples an appropriate selection of an energy region in the registered spectrum. On the basis of computer simulations the best counting conditions are selected for a thick lead sample in order to optimize the detection limit.
•Underground alpha spectrometry of thick sources.•Optimization of sensitivity of alpha spectrometers.•Reconstruction of the Po-210 diffusion profile in lead.
The GERmanium Detector Array (GERDA) experiment searched for the lepton-number-violating neutrinoless double-β (0νββ) decay of ^{76}Ge, whose discovery would have far-reaching implications in ...cosmology and particle physics. By operating bare germanium diodes, enriched in ^{76}Ge, in an active liquid argon shield, GERDA achieved an unprecedently low background index of 5.2×10^{-4} counts/(keV kg yr) in the signal region and met the design goal to collect an exposure of 100 kg yr in a background-free regime. When combined with the result of Phase I, no signal is observed after 127.2 kg yr of total exposure. A limit on the half-life of 0νββ decay in ^{76}Ge is set at T_{1/2}>1.8×10^{26} yr at 90% C.L., which coincides with the sensitivity assuming no signal.
For most of their existence, stars are fuelled by the fusion of hydrogen into helium. Fusion proceeds via two processes that are well understood theoretically: the proton-proton (pp) chain and the ...carbon-nitrogen-oxygen (CNO) cycle
. Neutrinos that are emitted along such fusion processes in the solar core are the only direct probe of the deep interior of the Sun. A complete spectroscopic study of neutrinos from the pp chain, which produces about 99 per cent of the solar energy, has been performed previously
; however, there has been no reported experimental evidence of the CNO cycle. Here we report the direct observation, with a high statistical significance, of neutrinos produced in the CNO cycle in the Sun. This experimental evidence was obtained using the highly radiopure, large-volume, liquid-scintillator detector of Borexino, an experiment located at the underground Laboratori Nazionali del Gran Sasso in Italy. The main experimental challenge was to identify the excess signal-only a few counts per day above the background per 100 tonnes of target-that is attributed to interactions of the CNO neutrinos. Advances in the thermal stabilization of the detector over the last five years enabled us to develop a method to constrain the rate of bismuth-210 contaminating the scintillator. In the CNO cycle, the fusion of hydrogen is catalysed by carbon, nitrogen and oxygen, and so its rate-as well as the flux of emitted CNO neutrinos-depends directly on the abundance of these elements in the solar core. This result therefore paves the way towards a direct measurement of the solar metallicity using CNO neutrinos. Our findings quantify the relative contribution of CNO fusion in the Sun to be of the order of 1 per cent; however, in massive stars, this is the dominant process of energy production. This work provides experimental evidence of the primary mechanism for the stellar conversion of hydrogen into helium in the Universe.
We present new constraints on sub-GeV dark-matter particles scattering off electrons based on 6780.0 kg d of data collected with the DarkSide-50 dual-phase argon time projection chamber. This ...analysis uses electroluminescence signals due to ionized electrons extracted from the liquid argon target. The detector has a very high trigger probability for these signals, allowing for an analysis threshold of three extracted electrons, or approximately 0.05 keVee. We calculate the expected recoil spectra for dark matter-electron scattering in argon and, under the assumption of momentum-independent scattering, improve upon existing limits from XENON10 for dark-matter particles with masses between 30 and 100 MeV/c^{2}.
A new detector for
222
Rn measurements in gases is described. It is based on the low temperature collection of radon on a stainless steel plate and subsequent counting of emitted alpha-particles ...using an ion-implanted silicon detector. A very low background of 25 counts/day for the
222
Rn energy window was achieved. High detection efficiency of 32% (2π geometry) and the large 65 liter volume of the detector allow radon measurements at the level of 12 mBq/m
3
with 30% accuracy (relative error). Behavior of the alpha-emitting radon daughters born on the cooled stainless steel plate,
218
Po and
214
Po, was also analyzed.
We present an investigation of the
222Rn concentration in argon with ultra-low background proportional counters. Argon purification tests by means of cryo-adsorption of radon on activated carbon were ...performed. For gaseous argon the purification process was found to be very efficient. Also in liquid phase the
222Rn concentration could be reduced significantly, however, the efficiency is lower than in the gas phase. We also have analyzed the initial
222Rn concentrations in commercial liquid argon. It was found to be significantly higher than in liquid nitrogen.
A search for the solar neutrino effective magnetic moment has been performed using data from 1291.5 days exposure during the second phase of the Borexino experiment. No significant deviations from ...the expected shape of the electron recoil spectrum from solar neutrinos have been found, and a new upper limit on the effective neutrino magnetic moment of μνeff<2.8×10−11 μB at 90% C.L. has been set using constraints on the sum of the solar neutrino fluxes implied by the radiochemical gallium experiments. Using the limit for the effective neutrino moment, new limits for the magnetic moments of the neutrino flavor states, and for the elements of the neutrino magnetic moments matrix for Dirac and Majorana neutrinos, are derived.
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