Limits on Ag-108m Decay Rate Variations due to Reactor Antineutrinos

An experiment is currently being conducted at the High Flux Isotope Reactor (HFIR) located at Oak Ridge National Laboratory (ORNL), designed to address whether a flux of reactor-generated antineutrinos, $\overline{\nu}_e$, can alter weak interaction nuclear decay life-times. The samples are exposed to approximately equal and alternating 28-day reactor-on periods, with an antineutrino flux of $\sim 3 \times 10^{12}$ cm$^{-2}$ s$^{-1}$, and reactor-off refueling periods. Accurately measuring the radioactive decay constant in a counting experiment requires that both the detector and environment be well understood and stable over the experimental duration. A High Purity Germanium spectrometer has been constructed 6 meters from the HFIR core with the sensitivity to detect deviations in the decay rate at the level of 1 part in $10^{5}$. In the $^{108m}$Ag study, both the electron capture decay to $^{108}$Pd and the internal conversion to $^{108}$Ag are measured. The internal transition is an electromagnetic process that should remain unaffected by the antineutrino flux, and thus it presents a useful tool to further reduce systematic uncertainties. Analysis of the branching fraction of the decay modes should increase the spectrometer's sensitivity to the level of $10^{-6}$.