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 Cr-51 was produced by irradiating 512.7 g of 92.4%-enriched Cr-50 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 Ge-71 by the inverse beta decay reaction Ga-71(nu(e),e(-))Ge-71 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 (expt)(-0.027)(+0.035) (theor) and to the cross section of Haxton is 0.87 +/- 0.11 (expt)+/- 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. [S0556-2813(99)03803-0].