Double-Beta Decay of $^{150}$Nd to Excited Final States

An experimental study of the two-neutrino double-beta (2$\nu\beta\beta$) decay of $^{150}$Nd to various excited final states of $^{150}$Sm was performed at Triangle Universities Nuclear Laboratory (TUNL). Such data provide important checks for theoretical models used to predict 0$\nu\beta\beta$ decay half lives. The measurement was performed at the recently established Kimballton Underground Research Facility (KURF) using the TUNL-ITEP $\beta\beta$ 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. This study yields the first results from KURF and the first detection of the coincidence gamma rays from the 0$^+_1$ excited state of $^{150}$Sm. These gamma rays have energies of 334.0 keV and 406.5 keV, and are emitted in coincidence through a 0$^+_1\rightarrow$2$^+_1\rightarrow$0$^+_{gs}$ transition. An enriched Nd$_2$O$_3$ sample obtained from Oak Ridge National Laboratory was used. After counting for 391 days, 29 raw events in the region of interest were observed. This count rate gives a half life of $T_{1/2}=(0.72^{+0.36}_{-0.18}\pm0.04(syst.))\times 10^{20}$ years, which agrees within error with another recent measurement, in which no coincidence was employed. An updated result will be given.