Search for 2β\ decays of 96Ru and 104Ru by ultra-low background HPGe gamma spectrometry at LNGS: final results
Abstract
An experiment to search for double beta decay processes in 96Ru and 104Ru, which are accompanied by gamma rays, has been realized in the underground Gran Sasso National Laboratories of the I.N.F.N. (Italy). Ruthenium samples with masses of about (0.5-0.7) kg were measured with the help of ultra-low background high purity Ge gamma 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+/ε β+/2ε\ processes in 96Ru have been established on the level of 1020 yr, in particular for decays to the ground state of 96Mo: T1/2(2 2β+) > 1.4 1020 yr, T1/2(2 εβ+) > 8.0 1019 yr and T1/2(0 2K) > 1.0 1021 yr (all limits are at 90% C.L.). The resonant neutrinoless double electron captures to the 2700.2 keV and 2712.7 keV excited states of 96Mo are restricted as: T1/2(0 KL) > 2.0 1020 yr and T1/2(0 2L) > 3.6 1020 yr, respectively. Various two neutrino and neutrinoless 2β\ half lives of 96Ru have been estimated in the framework of the QRPA approach. In addition, the T1/2 limit for 0 2β- transitions of 104Ru to the first excited state of 104Pd has been set as > 6.5 1020 yr.
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