Investigation of Double Beta Decay of 58Ni with the Obelix Spectrometer

Investigation of double beta decay processes (beta(+) EC, EC/EC) of Ni-58 was performed at the Modane underground laboratory (LSM, France, 4800 m w.e.) using ultra low-background HPGe detector Obelix with sensitive volume of 600 cm(3) and a sample of natural nickel, containing similar to 68% of Ni-58 with a mass of similar to 21.7 kg. New experimental limits on 2 nu beta(+) EC decay of Ni-58 to the ground 0(+) and 2(1)(+), 811 keV excited state of Fe-58, and 2 nu EC/EC decay of Ni-58 to 2(1)(+), 811 keV and 2(2)(+), 1 675 keV excited states of Fe-58 were obtained from the preliminary calculation of experimental data accumulated in similar to 88d. They are -T-1/2(beta(+) EC, 0(+) -> 0(+)) > 1.4 x10(21) y; T-1/2 (beta(+) EC, 0(+) -> 2(1)(+) > 1.7 x10(22) y, T-1/2 (EC/EC, 0(+) -> 2(1)(+)) > 2.4 x10(22) y, T-1/2 (EC/EC, 0(+) -> 2(2)(+)) > 2.1 x 10(22) y. For resonant neutrino-less radiative EC/EC decay with energy of 1 918.3 keV a new experimental limit of T-1/2 (0.EC/EC - res, 1918keV) > 4.7 x10(22) y was also obtained. All limits are at 90 % CL.