New limit on two neutrino electron capture with positron emission in 106Cd

An experiment to search for double beta processes in 106Cd is in progress with the help of 106CdWO4 crystal scintillator (enriched in 106Cd to 66%) in coincidence with two large volume CdWO4 crystal scintillators in close geometry at the Gran Sasso Underground Laboratory. The time resolution of the set-up was analyzed, and the methods of pulse-shape discrimination of α and γ(β) events was applied to estimate the radioactive contamination of the crystal and to reduce the background counting rate. The possible double beta decay processes and the background components have been simulated by a Monte Carlo method with GEANT4. The experimental sensitivity is approaching the theoretical predictions for the two-neutrino electron capture with positron emission in 106Cd: lim T1/2≥4×10^21 yr at 90% C.L. (the best previous limit was established in the previous stage of the experiment as T1/2≥1.1× 10^21 yr, while the theoretical predictions are in the region of T1/2∼10^21−10^22 yr)