Measurement of the response of a Ga solar neutrino experiment to neutrinos from a 37Ar source

An intense source of Ar-37 was produced by the (n,alpha) reaction on Ca-40 by irradiating 330 kg of calcium oxide in the fast neutron breeder reactor at Zarechny, Russia. The Ar-37 was released from the solid target by dissolution in acid, collected from this solution, purified, sealed into a small source, and brought to the Baksan Neutrino Observatory where it was used to irradiate 13 tonnes of gallium metal in the Russian-American gallium solar neutrino experiment SAGE. Ten exposures of the gallium to the source, whose initial strength was 409 +/- 2kCi, were carried out during the period April to September 2004. The Ge-71 produced by the reaction Ga-71(nu(e),e(-))Ge-71 was extracted, purified, and counted. The measured production rate was 11.0(-0.9)(+1.0) (stat)+/- 0.6 (syst) atoms of Ge-71/d, which is 0.79(-0.10)(+0.09) of the theoretically calculated production rate. When all neutrino source experiments with gallium are considered together, there is an indication the theoretical cross section has been overestimated.