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An intense source of 37 Ar was produced by the (n, α) reaction on 40 Ca by irradiating 330 kg of calcium oxide in the fast neutron breeder reactor at Zarechny, Russia. The 37 Ar 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 ± 2 kCi, were carried out during the period April to September 2004. The 71 Ge produced by the reaction 71 Ga(ν e , e − ) 71 Ge was extracted, purified, and counted. The measured production rate was 11.0 +1.0 −0.9 (stat) ± 0.6 (syst) atoms of 71 Ge/d, which is 0.79 +0.09 −0.10 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.

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