[en] The NEMO detector series is designed to search for the neutrinoless double β decay, which would prove that the neutrino is a Majorana particle (i.e. identical to its own antiparticle) and has a nonzero mass. After an introduction to neutrino physics and a description of both the NEMO 3 and SuperNEMO detectors, this thesis is articulated in two independent parts. The first provides an investigation of the neutron background in order to optimize the shielding for the first SuperNEMO module. The outcome of the study recommends the addition of borated polyethylene to the NEMO 3 shielding (on both sides of the iron shielding) to obtain a negligible background, coming from neutrons in the energy window of the two-electron channel where the neutrinoless double β decay of selenium- 82 is expected, for the duration of five years for which data will be taken with this first module. In the second part, the neodymium foil located in the NEMO 3 detector is deeply analyzed to obtain an indication of the standard double β decay of neodymium-150 to the 0₁⁺ excited state of samarium-150. The measured half-life, with a significance of 3.7σ, is: T_1/2(¹⁵⁰Nd_0⁺→0⁺1) = [7.12 ± 1.28 (stat.) ± 0.91 (syst.)] x 10¹⁹ years. (author)

[en] Integrated modeling of plasma-surface interactions (PSI) provides a comprehensive and self-consistent description, moving the field closer to developing predictive and design capabilities for plasma facing components. This technique, using descriptions for the scrape-off-layer plasma provided by SOLPS, the sheath by hPIC, ion-surface interactions by F-TRIDYN and the sub-surface by Xolotl, has been successfully applied to interpret and predict steady-state PSI experiments in current and future tokamaks [1–4]. Here we describe further developments in our workflow to incorporate time-dependence and two-way information flow, to model transient scenarios (e.g., ELMs). We predict the evolution of W samples pre-damaged by He and exposed to ELMy H-mode plasmas in the DIII-D DiMES [5]. This presentation will describe two simulations to predict dynamic recycling.

[en] In this manuscript we introduce a simulation tool-suite for predicting plasma-surface interactions (PSI), which aims to predict the evolution of the plasma-facing surfaces that continually change due to exposure to fusion plasmas. A comprehensive description of PSI involves a wide range of physical phenomena, of which we include components for (a) the gas implantation and its dynamic evolution below the divertor surface; (b) erosion of wall material; (c) transport and re-deposition of the eroded impurities; and (d) the scrape-off layer plasma including fuel ions and extrinsic impurities. These components are integrated to predict changes in surface morphology and fuel recycling, and the effect of material erosion and re-deposition in fuel retention. Integrated simulations for ITER-like parameters in a helium plasma environment are presented, focused on the response of the tungsten divertor. The model is also applied to predicting the response of the tungsten surface pre-damaged by He plasma, to burning plasma operations. This case further demonstrates the capability to model the effect of sub-surface helium dynamics, which include helium nucleation, clustering and the bursting of over-pressurized bubbles, its impact on fuel recycling as well as the effect of sputtering on the surface evolution. (topical issue article)

[en] We report results from the NEMO-3 experiment based on an exposure of 1275 days with 661 g of ¹³⁰Te in the form of enriched and natural tellurium foils. The ββ decay rate of ¹³⁰Te is found to be greater than zero with a significance of 7.7 standard deviations and the half-life is measured to be T_1/2^2ν=[7.0±0.9(stat)±1.1(syst)]x10²⁰ yr. This represents the most precise measurement of this half-life yet published and the first real-time observation of this decay.

[en] We report the results of a search for the neutrinoless double-β decay (0νββ) of ¹⁰⁰Mo, using the NEMO-3 detector to reconstruct the full topology of the final state events. With an exposure of 34.7 kg.y, no evidence for the 0νββ signal has been found, yielding a limit for the light Majorana neutrino mass mechanism of T_1/2 (0νββ≥ 1.1 * 10²⁴ years (90% C.L.) once both statistical and systematic uncertainties are taken into account. Depending on the nuclear matrix elements this corresponds to an upper limit on the Majorana effective neutrino mass of (m_ν ≤ 0.3-0.9 eV (90% C.L.). Constraints on other lepton number violating mechanisms of 0νββ decays are also given. Searching for high-energy double electron events in all suitable sources of the detector, no event in the energy region [3.2-10] MeV is observed for an exposure of 47 kg.y. (authors)

[en] The SuperNEMO experiment will search for neutrinoless double-beta decay (0νββ), and study the Standard-Model double-beta decay process (2νββ). The SuperNEMO technology can measure the energy of each of the electrons produced in a double-beta (ββ) decay, and can reconstruct the topology of their individual tracks. The study of the double-beta decay spectrum requires very accurate energy calibration to be carried out periodically. The SuperNEMO Demonstrator Module will be calibrated using 42 calibration sources, each consisting of a droplet of ²⁰⁷Bi within a frame assembly. The quality of these sources, which depends upon the entire ^207Bi droplet being contained within the frame, is key for correctly calibrating SuperNEMO's energy response. In this paper, we present a novel method for precisely measuring the exact geometry of the deposition of ²⁰⁷Bi droplets within the frames, using Timepix pixel detectors. We studied 49 different sources and selected 42 high-quality sources with the most central source positioning. (paper)

[en] The BiPo-3 detector, running at the Canfranc Underground Laboratory (Laboratorio Subterr and apos;aneo de Canfranc, LSC, Spain) since 2013, is a low-radioactivity detector dedicated to measuring ultra low natural radionuclide contaminations of "2"0"8Tl ("2"3"2Th chain) and "2"1"4Bi ("2"3"8U chain) in thin materials. The total sensitive surface area of the detector is 3.6 m"2. The detector has been developed to measure the radiopurity of the selenium double β-decay source foils of the SuperNEMO experiment. In this paper the design and performance of the detector, and results of the background measurements in "2"0"8Tl and "2"1"4Bi, are presented, and the validation of the BiPo-3 measurement with a calibrated aluminium foil is discussed. Results of the "2"0"8Tl and "2"1"4Bi activity measurements of the first enriched "8"2Se foils of the double β-decay SuperNEMO experiment are reported. The sensitivity of the BiPo-3 detector for the measurement of the SuperNEMO "8"2Se foils is A("2"0"8Tl) <2 μBq/kg (90% C.L.) and A("2"1"4Bi) <140 μBq/kg (90% C.L.) after 6 months of measurement.

[en] The BiPo-3 detector is a low radioactive detector dedicated to measuring ultra-low natural contaminations of "2"0"8Tl and "2"1"4Bi in thin materials, initially developed to measure the radiopurity of the double β decay source foils of the SuperNEMO experiment at the μBq/kg level. The BiPo-3 technique consists in installing the foil of interest between two thin ultra-radiopure scintillators coupled to low radioactive photomultipliers. The design and performances of the detector are presented. In this paper, the final results of the "2"0"8Tl and "2"1"4Bi activity measurements of the first enriched "8"2Se foils are reported for the first time, showing the capability of the detector to reach sensitivities in the range of some μBq/kg. - Highlights: • BiPo3 : low radioactive detector to measure ultra-low levels of "2"0"8Tl and "2"1"4Bi. • Backgrounds characterized. • Surface background : A("2"0"8Tl) =(0.9±0.2) μBq/m"2 and A("2"1"4Bi) =(1.0±0.3) μBq/m"2. • First SuperNemo double β source foils measured : A("2"0"8Tl) =(21±11) μBq/kg and A("2"1"4Bi) < 290 μBq/kg at 90% C.L. • Shows capability to measure "2"0"8Tl in the range of some μBq/kg.

[en] Double beta decay of ¹⁰⁰Mo to the excited states of daughter nuclei has been studied using a 600 cm³ low-background HPGe detector and an external source consisting of 2588 g of 97.5% enriched metallic ¹⁰⁰Mo, which was formerly inside the NEMO-3 detector and used for the NEMO-3 measurements of ¹⁰⁰Mo. The half-life for the two-neutrino double beta decay of ¹⁰⁰Mo to the excited 0₁⁺ state in ¹⁰⁰Ru is measured to be T_1/2=[7.5±0.6(stat)±0.6(syst)]⋅10²⁰ yr. For other (0ν+2ν) transitions to the 2₁⁺, 2₂⁺, 0₂⁺, 2₃⁺ and 0₃⁺ levels in ¹⁰⁰Ru, limits are obtained at the level of ∼(0.25–1.1)⋅10²² yr

[en] Using data from the NEMO-3 experiment, we have measured the two-neutrino double beta decay (2νββ) half-life of ⁸²Se as T_1/2^2ν = [9.39 ± 0.17(stat) ± 0.58(syst) ] x 10¹⁹ y under the single-state dominance hypothesis for this nuclear transition. The corresponding nuclear matrix element is vertical stroke M^2ν vertical stroke = 0.0498 ± 0.0016. In addition, a search for neutrinoless double beta decay (0νββ) using 0.93 kg of ⁸²Se observed for a total of 5.25 y has been conducted and no evidence for a signal has been found. The resulting half-life limit of T_1/2^0ν > 2.5 x 10²³ y (90% C.L.) for the light neutrino exchange mechanism leads to a constraint on the effective Majorana neutrino mass of left angle m_ν right angle < (1.2-3.0) eV, where the range reflects 0νββ nuclear matrix element values from different calculations. Furthermore, constraints on lepton number violating parameters for other 0νββ mechanisms, such as right-handed currents, majoron emission and R-parity violating supersymmetry modes have been set. (orig.)