Measurement of 130Te double beta decay process in the NEMO-3 experiment- R and D of SuperNEMO project: study of the BiPo detector

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: T2ν(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 massββ < 1.3 - 4.7 eV extracted from the limit on 2β0ν process of 130Te: T0ν(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: T0ν(1/2) > 3.0 1024 years and mββ < (0.19 - 0.68) eV. SuperNEMO is a project with 100 kg of 2β emitters, to search for 2β0ν process up to T0ν(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)