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 (2νββ) 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 100Mo 2νββ decay to the first excited state in 100Ru 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: . Measured 2νββ 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 100Ru which, if improved, may be of interest for more exotic conjectures, like a bosonic component to neutrino statistics.