The Russian-American Gallium Experiment (SAGE) Cr Neutrino Source Measurement

The solar neutrino capture rate measured by SAGE is well below that predicted by solar models. To check the overall experimental efficiency, we exposed 13 tonnes of Ga metal to a reactor-produced 517 kCi source of ${}^{51}$Cr. The ratio of the measured production rate to that predicted from the source activity is $0.95\ifmmode\pm\else\textpm\fi{}0.11(\mathrm{stat})+0.05/\ensuremath{-}0.08(\mathrm{syst})$. This agreement verifies that the experimental efficiency is measured correctly, establishes that there are no unknown systematic errors at the 10% level, and provides considerable evidence for the reliability of the solar neutrino measurement.