Measurement of the response of a gallium metal solar neutrino experiment to neutrinos from a 51Cr 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 51Cr was produced by irradiating 512.7 g of 92.4%-enriched 50Cr 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 tonne target of liquid gallium and the cross section for the production of 71Ge by the inverse beta decay reaction was measured to be (5.55 +/- 0.60 (stat.) +/- 0.32 (syst.)) x 10^(-45) cm^2. The ratio of this cross section to the theoretical cross section of Bahcall for this reaction is 0.95 +/- 0.12 (exp.) +/- 0.03 (theor.) and to the cross section of Haxton is 0.87 +/- 0.11 (exp.) +/- 0.09 (theor.). This good agreement between prediction and observation implies that the overall experimental efficiency for the solar neutrino measurements is correctly determined and provides considerable evidence for the reliability of the solar neutrino measurement.Comment: 20 pages including figures in two column forma