Production and Decay of the Ge73-m Metastable State in a Low-Background Germanium Detector

Abstract

The $\ge 73m$ metastable states decay with a very characteristic signature which allow them to be tagged event-by-event. Studies were performed using data taken with a high-purity germanium detector in a low-background laboratory near a nuclear power reactor core where $\nuebar$-flux was $6.4\times 10^{12}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$. The measured average and equilibrium production rates of $\ge 73m$ were $(8.7\pm 0.4)$ and $(6.7\pm 0.3)\mathrm{k}{\mathrm{g}}^{-1}\mathrm{da}{\mathrm{y}}^{-1}$, respectively. The production channels were studied and identified. By studying the difference in the production of $\ge 73m$ between the reactor ON and OFF spectra, the limiting sensitivities at the range of $\sim 10^{-42}-10^{-43}\mathrm{c}{\mathrm{m}}^2$ for the cross-sections of neutrino-induced nuclear transitions were derived. The dominant background are due to $\beta$-decays of cosmic-ray induced ${}^{73}$Ga. The prospects of enhancing the sensitivities at underground locations are discussed.

16 pages, 10 figures