Status of the R2D2 project: A future neutrinoless double beta decay experiment

The nature of the neutrino is a central questions in physics. The search for neutrinoless double beta decay is the most sensitive experimental approach to demonstrate that the neutrino is a Majorana particle. Observation of such a rare process demands a detector with an excellent energy resolution, extremely low background, and a large mass of a double beta decaying isotope. R2D2 aims to develop a novel spherical high-pressure TPC that meets all the above requirements. As a first step, the energy resolution of the R2D2 prototype was measured. A 1.1% (FWHM) energy resolution was achieved for 5.3 MeV α-particles in Ar:CH4 at pressure up to 1.1 bar. This is a major milestone for R2D2 and paves the way for further studies with Xe gas and the possible use of this technology for neutrinoless double beta decay searches.

Development of methods for the preparation of radiopure 82Se sources for the SuperNEMO neutrinoless double-beta decay experiment

A radiochemical method for producing82Se sources with an ultra-low level of contamination of natural radionuclides (40K, decay products of232Th and238U) has been developed based on cation-exchange chromatographic purification with reverse removal of impurities. It includes chromatographic separation (purification), reduction, conditioning (which includes decantation, centrifugation, washing, grinding, and drying), and82Se foil production. The conditioning stage, during which highly dispersed elemental selenium is obtained by the reduction of purified selenious acid (H2SeO3) with sulfur dioxide (SO2) represents the crucial step in the preparation of radiopure82Se samples. The natural selenium (600 g) was first produced in this procedure in order to refine the method. The technique developed was then used to produce 2.5 kg of radiopure enriched selenium (82Se). The produced82Se samples were wrapped in polyethylene (12 μm thick) and radionuclides present in the sample were analyzed with the BiPo-3 detector. The radiopurity of the plastic materials (chromatographic column material and polypropylene chemical vessels), which were used at all stages, was determined by instrumental neutron activation analysis. The radiopurity of the82Se foils was checked by measurements with the BiPo-3 spectrometer, which confirmed the high purity of the final product. The measured contamination level for208Tl was 8–54 μBq/kg, and for214Bi the detection limit of 600 μBq/kg has been reached.