[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] 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.)