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An experiment to search for double-β decay processes in 96Ru and 104Ru, which are accompanied by γ rays, has been realized in the underground Gran Sasso National Laboratories of the I.N.F.N. (Italy). Ruthenium samples with masses of ≈0.5–0.7 kg were measured with the help of ultralow-background high-purity Ge γ -ray spectrometry. After 2162 h of data taking the samples were deeply purified to reduce the internal contamination of 40K. The last part of the data has been accumulated over 5479 h. New improved half-life limits on 2β+/εβ+/2ε processes in 96Ru have been established on the level of 1020 yr, in particular for decays to the ground state of 96Mo: T 2ν2β+ 1/2 1.4 × 1020 yr, T 2νεβ+ 1/2 8.0 × 1019 yr, and T 0ν2K 1/2 1.0 × 1021 yr (all limits are at 90% C.L.). The resonant neutrinoless double-electron captures to the 2700.2 and 2712.7 keV excited states of 96Mo are restricted as T 0νKL 1/2 2.0 × 1020 yr and T 0ν2L 1/2 3.6 × 1020 yr, respectively. Various two-neutrino and neutrinoless 2β half-lives of 96Ru have been estimated in the framework of the quasiparticle random-phase approximation approach. In addition, the T1/2 limit for 0ν2β− transitions of 104Ru to the first excited state of 104Pd has been set as 6.5 × 1020 yr.
A search for double β processes in 106Cd was carried out at the Gran Sasso National Laboratories of the INFN (Italy) with the help of a 106CdWO4 crystal scintillator (215 g) enriched in 106Cd up to 66%. After 6590 h of data taking, new improved half-life limits on the double β decay processes in 106Cd were established at the level of 1019–1021 yr; in particular, T 2νεβ+ 1/2 2.1 × 1020 yr, T 2ν2β+ 1/2 4.3 × 1020 yr, and T 0ν2ε 1/2 1.0 × 1021 yr. The resonant neutrinoless double-electron captures to the 2718-, 2741-, and 2748-keV excited states of 106Pd are restricted to T 0ν2K 1/2 4.3 × 1020 yr, T 0νKL1 1/2 9.5 × 1020 yr, and T 0νKL3 1/2 4.3 × 1020 yr, respectively (all limits at 90% confidence level). A possible resonant enhancement of the 0ν2ε processes is estimated in the framework of the quasiparticle random phase approximation (QRPA) approach. Radioactive contamination of the 106CdWO4 crystal scintillator is reported.
A search for double β processes in 106Cd was carried out at the Gran Sasso National Laboratories of the INFN (Italy) by using a CdWO4 crystal scintillator (mass of 215 g) enriched in 106Cd up to 66%. After 6590 h of data taking, half-life limits on double beta processes in 106Cd were set at level of 1019 −1021 yr. A possible resonant enhancement of the 0ν2ε processes has also been estimated in the framework of the QRPA approach.