Physics – Nuclear Physics – Nuclear Experiment
Scientific paper
2011-12-05
Physics
Nuclear Physics
Nuclear Experiment
Ph.D. thesis (in Ukrainian), 188 pages, 47 figures, 29 tables, and 259 references. Title, abstract and contents of the thesis
Scientific paper
The results of the experimental investigations of double beta processes in Zinc and Tungsten isotopes with the help of middle volume (117 g, 168 g and 699 g) low-background ZnWO_4 crystal scintillators are presented. The experiment was carried out in the low-background "DAMA/R&D" set-up at the Gran Sasso National Laboratories of the INFN (Italy) at a depth of \approx3600 m w.e. The total measurement time exceeds ten thousand hours. New improved half-life limits on double electron capture and electron capture with positron emission in ^{64}Zn have been set: T^{2\nu 2K}_{1/2}(^{64}Zn) \geq 6.2(6.3) \times 10^{18} yr, T^{0\nu 2\epsilon}_{1/2} (^{64}Zn) \geq 1.1(2.8) \times 10^{20} yr, T^{2\nu \epsilon \beta^+}_{1/2}(^{64}Zn) \geq 0.7(2.1) \times 10^{21} yr, and T^{0\nu \epsilon \beta^+}_{1/2}(^{64}Zn) \geq 4.3(5.7) \times 10^{20} yr, all the limits are at 90% (68%) C.L. The positive indication on the \epsilon \beta^+ decay of ^{64}Zn with T^{(2\nu + 0\nu) \epsilon \beta^+}_{1/2} (^{64}Zn) = (1.1 \pm 0.9) \times 10^{19} yr suggested in [Appl. Radiat. Isot. 46 (1995) 455-456] is fully discarded by the present experiment. The half-life limits on the 2\beta processes in ^{70}Zn, ^{180}W, and two neutrino mode of 2\beta^- decay in ^{186}W established in the present work on the level of 10^{17}-10^{20} yr are one order of magnitude higher than those set in previous experiments. Energy resolution, relative light output, \alpha/\beta ratio, decay time, pulse-shape discrimination between \alpha particles and \gamma rays (\beta particles), and radioactive contamination of CdWO_4, PbWO_4 (undoped, and doped by F, Eu, Mo, Gd, S), and ZnWO_4 crystal scintillators were studied. Applicability of these scintillators to search for double beta decay was proved.
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