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

TL;DR

This study investigates the production and decay of the Ge73-m metastable state in a germanium detector near a nuclear reactor, measuring production rates, identifying channels, and setting limits on neutrino-induced transition cross-sections.

Contribution

It provides the first detailed measurement of Ge73-m production rates and identifies the dominant background sources in a low-background detector environment.

Findings

Measured average production rate: (8.7 ± 0.4) kg⁻¹ day⁻¹

Determined equilibrium production rate: (6.7 ± 0.3) kg⁻¹ day⁻¹

Set sensitivity limits for neutrino-induced transitions: ~10⁻⁴² to 10⁻⁴³ cm²

Abstract

The $\ge73m$ 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 $\rm{6.4 \times 10^{12} ~ cm^{-2} s^{-1}}$. The measured average and equilibrium production rates of $\ge73m$ were $\rm{(8.7 \pm 0.4)}$ and $\rm{(6.7 \pm 0.3) ~ kg^{-1} day^{-1}}$, respectively. The production channels were studied and identified. By studying the difference in the production of $\ge73m$ between the reactor ON and OFF spectra, the limiting sensitivities at the range of $\rm{\sim 10^{-42} - 10^{-43} ~ cm^2}$ 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.