Measurement of the response of a gallium metal solar neutrino experiment to neutrinos from a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow/><mml:mrow><mml:mn>51</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">Cr</mml:mi></mml:math>source

The neutrino capture rate measured by the Russian-American Gallium Experiment is well below that predicted by solar models. To check the response of this experiment to low-energy neutrinos, a 517 kCi source of ${}^{51}$Cr was produced by irradiating 512.7 g of 92.4%-enriched ${}^{50}$Cr in a high-flux fast neutron reactor. This source, which mainly emits monoenergetic 747-keV neutrinos, was placed at the center of a 13.1 ton target of liquid gallium and the cross section for the production of ${}^{71}$Ge by the inverse beta decay $\mathrm{reaction}{ }^{71}\mathrm{Ga}({\ensuremath{\nu}}_{e}{,e}^{\ensuremath{-}}{)}^{71}\mathrm{Ge}$ was measured to be $[5.55\ifmmode\pm\else\textpm\fi{}0.60(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.32(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}45}{\mathrm{cm}}^{2}.$ The ratio of this cross section to the theoretical cross section of Bahcall for this reaction is 0.95 \ifmmode\pm\else\textpm\fi{}0.12 ${(\mathrm{expt})}_{\ensuremath{-}0.027}^{+0.035}$ (theor) and to the cross section of Haxton is 0.87\ifmmode\pm\else\textpm\fi{}0.11 (expt)\ifmmode\pm\else\textpm\fi{}0.09 (theor). This good agreement between prediction and observation implies that the overall experimental efficiency is correctly determined and provides considerable evidence for the reliability of the solar neutrino measurement.