New Phase of the 116Cd 2β-decay experiment with 116CdWO4 scintillators

A new step of the Cd-116 2 beta-decay experiment is in progress at the Solotvina Underground Laboratory, The upgraded setup consists of four enriched (CdWO4)-Cd-116 crystal scintillators of total mass 339 g. As an active shield, 15 CdWO4 crystals (20.6 kg) are used. The background rate (in the energy interval 2.7-2.9 MeV) is 0.06 count/(yr kg keV), one order of magnitude lower than in the previous apparatus. Combined with results of preceding measurements, the half-life limit for the neutrinoless 2 beta decay of Cd-116 to the ground stare of Sn-116 is determined as T-1/2(0v) greater than or equal to 5.1 X 10(22) yr with 90% C.L. The limits on T-1/2 for transitions to the excited 2(1)(+) and 0(1)(+) levels of Sn-116 are 8.6 x 10(21) and 4.1 x 10(21) yr, respectively (at a 90% C.L.). For 0v2 beta decay accompanied by the emission of one and two Majorons, the constraints on the half-life: are T-1/2(0VM1) greater than or equal to 1.4 x 10(21) yr and T-1/2 (0vM2) greater than or equal to 4.1 x 10(20) yr (at a 90% C.L.). The corresponding constraints on the neutrino mass and the neutrino-Majoron coupling constant are (m(v)) less than or equal to 3.1 eV and (g(M)) less than or equal to 1.9 x 10(-4), respectively. (C) 2000 MAIK "Nauka/Interperiodica".