New measurements of ${}^{71}\mathrm{Ge}$ decay: Impact on the gallium anomaly

A dedicated high-statistics measurement of the ${}^{71}\mathrm{Ge}$ half-life is found to be in accurate agreement with an accepted value of $11.43\pm 0.03$ d, eliminating a recently proposed route to bypass the “gallium anomaly” affecting several neutrino experiments. Our data also severely constrain the possibility of ${}^{71}\mathrm{Ge}$ decay to low-energy excited levels of the ${}^{71}\mathrm{Ga}$ daughter nucleus as a solution to this puzzle. Additional unpublished measurements of this decay are discussed. Following the incorporation of this information, the gallium anomaly survives with high statistical significance.

Figure 1

${}^{71}\mathrm{Ge}$ decay rates in the present measurement (top) and the detector in [14] (bottom). Vertical (statistical) error bars are encumbered by the data points. Insets show the relative probability of EC from $L$ and $K$ shells. These include a small ($<<1\%$) correction for x-ray escape from each crystal. Red lines are exponential fits to the data (constant for insets).

Figure 2

Pre- and postactivation spectra. Two enhanced peaks from ${}^{71}\mathrm{Ge}$ decay are the only significant difference (a feature from ${}^{226}\mathrm{Ra}$ at 186.2 keV appears with compatible rate in both data sets). Example signatures (colored peaks) from decays to new excited ${}^{71}\mathrm{Ga}$ levels with sufficient BR to relax the evidence for the gallium anomaly are shown. These are strongly disfavored (see text).