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تسجيل مستخدم جديدSearch for Rare Nuclear Decays with HPGe Detectors at the STELLA Facility of the LNGS
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Results on the search for rare nuclear decays with the ultra low background facility STELLA at the LNGS using gamma ray spectrometry are presented. In particular, the best T1/2 limits were obtained for double beta processes in 96Ru and 104Ru. Several isotopes, which potentially decay through different double beta decay channels, including also possible resonant double electron captures, were investigated for the first time (156Dy, 158Dy, 184Os, 192Os, 190Pt, 198Pt). Search for resonant absorption of solar 7Li axions in a LiF crystal gave the best limit for the mass of 7Li axions (< 8.6 keV). Rare alpha decay of 190Pt to the first excited level of 186Os (Eexc = 137.2 keV) was observed for the first time.
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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 2beta+/epsilon beta+/2epsilon processes in 96Ru have been established on the level of 10^{20} yr, in particular for decays to the ground state of 96Mo: T1/2(2 u 2beta+) > 1.4 10^{20} yr, T1/2(2 u epsilonbeta+) > 8.0 10^{19} yr and T1/2(0 u 2K) > 1.0 10^{21} 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 u KL) > 2.0 10^{20} yr and T1/2(0 u 2L) > 3.6 10^{20} yr, respectively. Various two neutrino and neutrinoless 2beta half lives of 96Ru have been estimated in the framework of the QRPA approach. In addition, the T1/2 limit for 0 u 2beta- transitions of 104Ru to the first excited state of 104Pd has been set as > 6.5 10^{20} yr.
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