New results for double-beta decay of 100Mo to excited final states of 100Ru using the TUNL-ITEP apparatus

The coincidence detection efficiency of the TUNL-ITEP apparatus designed for measuring half-life times of two-neutrino double-beta (2 nu beta beta) decay transitions to excited final states in daughter nuclei has been measured with a factor of 2.4 improved accuracy. In addition, the previous measuring time of 455 days for the study of the Mo-100 2 nu beta beta decay to the first excited 0(1)(+) state in Ru-100 has been increased by 450 days, and a new result (combined with the previous measurement obtained with the same apparatus) for this transition is presented: T-1/2 = [5.5(-0.8)(+1.2)(stat) +/- 0.3(syst)] x 10(20) yr. Measured 2 nu beta beta decay half-life times to excited states can be used to test the reliability of nuclear matrix element calculations needed for determining the effective neutrino mass from zero-neutrino double-beta decay data. We also present new limits for transitions to higher excited states in Ru-100 which, if improved, may be of interest for more exotic conjectures, like a bosonic component to neutrino statistics. (C) 2009 Elsevier B.V. All rights reserved.