Search for double- $ \beta$ decays of 96Ru and 104Ru by ultra-low background HPGe $ \gamma$ spectrometry.

A search for double- $ \beta$ processes in 96Ru and 104Ru was realized in the underground Gran Sasso National Laboratories of the INFN (Italy) with the help of ultra-low background HPGe $ \gamma$ spectrometry. After 158h of data taking with 473g ruthenium sample, new improved limits on double-beta processes in 96Ru have been established on the level of 1018-1019yr. For the first time the double-beta decay of 104Ru to the 2+ 1 excited level of 104Pd has been restricted as T1/2 > 3.5×1019 yr. [ABSTRACT FROM AUTHOR]