New observation of 2β2ν decay of 100Mo to the 01+ level of 100Ru in the ARMONIA experiment

A sample of (MoO3)-Mo-100 powder with molybdenum enriched in Mo-100 to 99.5% and mass of 1199 g was measured for 18120 h in a low-background set-up with 4 HP Ge detectors (similar or equal to 225 cm(3) volume each one) deep underground (3600 m we) at the Laboratori Nazionali del Gran Sasso of the INFN (Italy) The two y quanta of 540 keV and of 591 keV emitted in the deexcitation process after a 2 beta 2 nu decay of 199Mo to the 01- excited level of Ru-100 (E-exc = 1131 keV) are observed in the accumulated data both in coincidence and in the I-dimensional sum spectrum. The measured half life is. T112 = 6 91 98(stat) 0.7(syst.) x 10213 yr, well in agreement with positive results obtained in previous experiments Moreover, the limit on charge non-conserving fi decay of Mo-100 is also set tau(CNC) > 4 5 x 10(19) yr at 90% C L.it corresponds to the limit on CNC admixture in weak currents epsilon(2)(v) < 2.9 x 10(-21). (C) 2010 Elsevier B.V. All rights reserved.