[en] This thesis contains 2 parts: data analysis of the NEMO-3 experiment data and a study of a BiPo detector for the SuperNEMO project. NEMO-3 is searching for neutrinoless double beta decay process 2β0ν using direct detection of the 2 emitted electrons by a tracking detector coupled to a calorimeter. I completely studied the backgrounds in several analysis channels and gave the most accurate measurement of the allowed process with neutrinos emission for ¹³⁰Te: T^2ν(1/2) equals (6.1 ± 1.2 (stat) ± 0.6 (syst)) 10²⁰ years. This result allows a good knowledge of the ultimate 2β2ν background for 2β0ν process research and helps to constrain or check the theoretical calculations of nuclear matrix elements, which have to be known with a good precision to determine the neutrino effective mass in case of 2β0ν observation. From NEMO-3 data, I also gave a limit on this effective neutrino mass_ββ < 1.3 - 4.7 eV extracted from the limit on 2β0ν process of ¹³⁰Te: T^0ν(1/2) > 6.3 10²² years. Due to the low mass of ¹³⁰Te contained in NEMO-3 (454 g), this result is not competitive with the limit recently published by CUORICINO for this isotope: T^0ν(1/2) > 3.0 10²⁴ years and m_ββ < (0.19 - 0.68) eV. SuperNEMO is a project with 100 kg of 2β emitters, to search for 2β0ν process up to T^0ν(1/2) > 10²⁶ years, using the NEMO-3 detection principle but improving efficiency, radio-purity, energy resolution and reducing backgrounds. This background will be then limited by natural radioactive contaminations inside the source foils. Thus the SuperNEMO specifications concerning the source foil radio-purity are very high: A(²⁰⁸Tl) < 2 μBq/kg and A(²¹⁴Bi) < 10 μBg/kg, and not measurable by actual detectors. The collaboration decided to study a BiPo detector to measure ²⁰⁸Tl and ²¹⁴Bi contaminations, using identification of the Bi → Po chains. Foil source to measure is put between two scintillator planes allowing energy and time measurements. I studied BiPo-1 prototype, showed its technical feasibility, validated the principle and determined the sensitivity of the source measurement compared to backgrounds. Data analysis of BiPo-1 showed the possibility to measure 5 μBq/kg of ²⁰⁸Tl with the final BiPo. This result is not so far from SuperNEMO requirements and already shows a gain factor of 4 compared to actual detection possibilities. (author)

[en] The BiPo project is dedicated to the measurement of extremely low radioactivity contamination of SuperNEMO source foils (208Tl < 2 μBq/kg and 214Bi < 10 μBq/kg). The R and D phase is started : a modular BiPo prototype with its shielding test facility is under construction. The goal of this prototype is to study the background and particularly the surface contamination of scintillators. The first capsule has been installed in the Canfranc Underground Laboratory in October, 17th and is now taking data. After 10.7 days of measurements, a preliminary upper limit on the surface radiopurity of the scintillators of A(208Tl) < 60 μBq/m2 (90% C. L.) has been obtained

[en] The BiPo project is dedicated to the measurement of extremely low radioactive contaminations of SuperNEMO ββ source foils (²⁰⁸Tl < 2 μBq/kg and ²¹⁴Bi < 10 μBq/kg). A modular BiPo1 prototype with its 20 modules and its shielding test facility is running in the Modane Underground Laboratory since February, 2008. The goal of this prototype is to study the backgrounds and particularly the surface contamination of plastic scintillators. After 3 months, a preliminary upper limit on the sensitivity of a 12 m² BiPo detector in ²⁰⁸Tl contamination of selenium source foils can be extrapolated to: A(²⁰⁸Tl) < 7.5 μBq/kg (90% C.L.)

[en] SuperNEMO is a double-$\beta$ decay experiment, which will employ the successful tracker–calorimeter technique used in the recently completed NEMO-3 experiment. SuperNEMO will implement 100 kg of double-$\beta$ decay isotope, reaching a sensitivity to the neutrinoless double-$\beta$ decay ($0\nu \beta \beta$) half-life of the order of $10^{26}$ yr, corresponding to a Majorana neutrino mass of 50–100 meV. One of the main goals and challenges of the SuperNEMO detector development programme has been to reach a calorimeter energy resolution, $\Delta \mathrm{E}∕\mathrm{E}$, around $3\text{\%}∕\sqrt{\mathrm{E}}\left(\mathrm{MeV}\right)$ $\sigma$, or $7\text{\%}∕\sqrt{\mathrm{E}}\left(\mathrm{MeV}\right)$ FWHM (full width at half maximum), using a calorimeter composed of large volume plastic scintillator blocks coupled to photomultiplier tubes. We describe the R&D programme and the final design of the SuperNEMO calorimeter that has met this challenging goal.

[en] This second topical workshop in low radioactivity techniques is intended to bring together experts in the field of low background techniques, especially applied to dark matter experiments, double beta decay experiments and neutrino detection in underground laboratories. This workshop has been organized into 7 sessions: 1) underground facilities (where a worldwide review is made), 2) neutron and muon induced background, isotope production, 3) low background counting techniques and low background detectors, 4) techniques for radon reduction, purified noble gases and liquid scintillator purification, 5) low levels on Pb-Bi-Po²¹⁰ and surface background, 6) low radioactivity detector components and material purification, and 7) low radioactive techniques in other applications (particularly to check the geographical origin of food-products or to date wine. This document is made up of the slides of the presentations

[en] The half-life for double-β decay of ¹⁵⁰Nd has been measured by the NEMO-3 experiment at the Modane Underground Laboratory. Using 924.7 days of data recorded with 36.55 g of ¹⁵⁰Nd, we measured the half-life for 2νββ decay to be T_1/2^2ν=(9.11_-0.22^+0.25(stat.)±0.63(syst.))x10¹⁸ yr. The observed limit on the half-life for neutrinoless double-β decay is found to be T_1/2^0ν>1.8x10²² yr at 90% confidence level. This translates into a limit on the effective Majorana neutrino mass of ν><4.0-6.3 eV if the nuclear deformation is taken into account. We also set limits on models involving Majoron emission, right-handed currents, and transitions to excited states.

[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 next generation of very-short-baseline reactor experiments will require compact detectors operating at surface level and close to a nuclear reactor. This paper presents a new detector concept based on a composite solid scintillator technology. The detector target uses cubes of polyvinyltoluene interleaved with ⁶LiF:ZnS(Ag) phosphor screens to detect the products of the inverse beta decay reaction. A multi-tonne detector system built from these individual cells can provide precise localisation of scintillation signals, making efficient use of the detector volume. Monte Carlo simulations indicate that a neutron capture efficiency of over 70 % is achievable with a sufficient number of ⁶LiF:ZnS(Ag) screens per cube and that an appropriate segmentation enables a measurement of the positron energy which is not limited by γ-ray leakage. First measurements of a single cell indicate that a very good neutron-gamma discrimination and high neutron detection efficiency can be obtained with adequate triggering techniques. The light yield from positron signals has been measured, showing that an energy resolution of 14%/√ E (MeV) is achievable with high uniformity. A preliminary neutrino signal analysis has been developed, using selection criteria for pulse shape, energy, time structure and energy spatial distribution and showing that an antineutrino efficiency of 40% can be achieved. It also shows that the fine segmentation of the detector can be used to significantly decrease both correlated and accidental backgrounds.

[en] This paper presents a comprehensive optimisation study to maximise the light collection efficiency of scintillating cube elements used in the SoLid detector. Very short baseline reactor experiments, like SoLid, look for active to sterile neutrino oscillation signatures in the anti-neutrino energy spectrum as a function of the distance to the core and energy. Performing a precise search requires high light yield of the scintillating elements and uniformity of the response in the detector volume. The SoLid experiment uses an innovative hybrid technology with two different scintillators: polyvinyltoluene scintillator cubes and ⁶LiF:ZnS(Ag) screens. A precision test bench based on a ²⁰⁷Bi calibration source has been developed to study improvements on the energy resolution and uniformity of the prompt scintillation signal of antineutrino interactions. A trigger system selecting the 1 MeV conversion electrons provides a Gaussian energy peak and allows for precise comparisons of the different detector configurations that were considered to improve the SoLid detector light collection. The light collection efficiency is influenced by the choice of wrapping material, the position of the ⁶LiF:ZnS(Ag) screen, the type of fibre, the number of optical fibres and the type of mirror at the end of the fibre. This study shows that large gains in light collection efficiency are possible compared to the SoLid SM1 prototype. The light yield for the SoLid detector is expected to be at least 52±2 photo-avalanches per MeV per cube, with a relative non-uniformity of 6 %, demonstrating that the required energy resolution of at least 14 % at 1 MeV can be achieved.