Measurement of the response of a Ga solar neutrino experiment to neutrinos from aAr37source

An intense source of ${}^{37}\mathrm{Ar}$ was produced by the $(n,\alpha )$ reaction on ${}^{40}\mathrm{Ca}$ by irradiating 330 kg of calcium oxide in the fast neutron breeder reactor at Zarechny, Russia. The ${}^{37}\mathrm{Ar}$ 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 $409\pm 2$kCi, were carried out during the period April to September 2004. The ${}^{71}\mathrm{Ge}$ produced by the reaction ${}^{71}\mathrm{Ga}({\nu }_e,e^{-}){}^{71}\mathrm{Ge}$ was extracted, purified, and counted. The measured production rate was $11.0_{-0.9}^{+1.0}\text{(stat)}\pm 0.6\text{(syst)}$ atoms of ${}^{71}\mathrm{Ge}$/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.