Abstract:
<p>An experimental study of the two-neutrino double-beta (2νββ) decay of <super>150</super>Nd to various excited final states of <super>150</super>Sm was performed at Triangle Universities Nuclear Laboratory (TUNL). Such data provide important checks for theoretical models used to predict 0νββ decay half lives.</p>
<p>The measurement was performed at the recently established Kimballton Underground Research Facility (KURF) in Ripplemeade, Virginia using the TUNL-ITEP double-beta decay setup. In this setup, two high-purity germanium detectors were operated in coincidence to detect the deexcitation gamma rays of the daughter nucleus. This coincidence technique, along with the location underground, provides a considerable reduction in background in the regions of interest.</p>
<p>This study yields the first results from KURF and the first detection of the</p>
<p>coincidence gamma rays from the 0<super>+</super><sub>1</sub> excited state of <super>150</super>Sm. These gamma rays</p>
<p>have energies of 334.0 keV and 406.5 keV, and are emitted in coincidence through a 0<super>+</super><sub>1</sub>→2<super>+</super><sub>1</sub>→0<super>+</super><sub>gs</sub> transition. The enriched Nd<sub>2</sub>O<sub>3</sub> sample obtained from Oak Ridge</p>
<p>National Laboratory consists of 40.13 g <super>150</sub>Nd. This sample was observed for 391 days, producing 29 raw events in the region of interest. This count rate gives a half life of T<sub>1/2</sub> = (0.72<super>+0.36</super><sub>−0.18</sub> ± 0.04(syst.)) × 10<super>20</super> years, which agrees within error with</p>
<p>another recent measurement, in which only the single deexcitation gamma rays were detected (i.e., no coincidence was employed). Lower limits were also obtained for decays to higher excited final states.</p>
