[en] An intense source of ³⁷Ar was produced by the (n, α) reaction on ⁴⁰Ca by irradiating calcium oxide in the fast neutron breeder reactor at Zarechny, Russia. The ³⁷Ar was released from the solid target, sealed into a small source, and was used to irradiate 13 tonnes of gallium metal in the Russian-American gallium solar neutrino experiment SAGE. The initial source strength was 409 ± 2 kCi. The measured production rate of ⁷¹Ge on gallium metal was 11.0^+1.0_-0.9 (stat) ± 0.6 (syst.) atoms per day, which is 0.79^+0.09_-0.10 of the theoretically calculated production rate

[en] We discuss the development of a spectrometer based on full energy absorption using liquid scintillator doped with enriched ⁶Li. Of specific interest, the spectrometer is expected to have good pulse height resolution, estimated to lie in the range 10-15% for 14-MeV neutrons. It should be sensitive to flux rates from 10^-6 cm^-2 s^-1 to 10⁶ cm^-2 s^-1 above a threshold of 500 keV in an uncorrelated γ background of up to 10⁴ s^-1. We have constructed a pilot version of the detector using undoped liquid scintillator, and we report its present status. The detector's efficiency is determined by the volume of the scintillator (∼1.21) and is estimated to be 0.2-0.5% for 3-MeV neutrons. The good pulse height resolution is achieved by compensation of the nonlinear light yield of the scintillator due to the use of optically separated segments, which collect scintillations from each recoil proton separately. We demonstrate here the response of the detector to neutrons from a Pu-α-Be source, whose energies range up to 10 MeV. Initial testing indicates a low threshold (∼600 keV) and good spectral response after requiring a multiplicity of three segments. Such a spectrometer has applications for low-background experiments in fundamental physics research, characterizations of neutron flux in space, and the health physics community

[en] The Russian-American experiment SAGE began to measure the solar neutrino capture rate with a target of gallium metal in December 1989. Measurements have continued with only a few brief interruptions since that time. In this article we present the experimental improvements in SAGE since its last published data summary in December 2001. Assuming the solar neutrino production rate was constant during the period of data collection, combined analysis of 168 extractions through December 2007 gives a capture rate of solar neutrinos with energy more than 233 keV of 65.4_-3.0^+3.1 (stat) _-2.8^+2.6 (syst) SNU. The weighted average of the results of all three Ga solar neutrino experiments, SAGE, Gallex, and GNO, is now 66.1±3.1 SNU, where statistical and systematic uncertainties have been combined in quadrature. During the recent period of data collection a new test of SAGE was made with a reactor-produced ³⁷Ar neutrino source. The ratio of observed to calculated rates in this experiment, combined with the measured rates in the three prior ⁵¹Cr neutrino-source experiments with Ga, is 0.87±0.05. A probable explanation for this low result is that the cross section for neutrino capture by the two lowest-lying excited states in ⁷¹Ge has been overestimated. If we assume these cross sections are zero, then the standard solar model including neutrino oscillations predicts a total capture rate in Ga in the range of 63 SNU to 66 SNU with an uncertainty of about 4%, in good agreement with experiment. We derive the current value of the neutrino flux produced in the Sun by the proton-proton fusion reaction to be φ_pp^·=(6.0±0.8)x10¹⁰/(cm² s), which agrees well with the pp flux predicted by the standard solar model. Finally, we make several tests and show that the data are consistent with the assumption that the solar neutrino production rate is constant in time.

[en] The Russian-American solar neutrino experiment has measured the capture rate of neutrinos on metallic gallium in a radiochemical experiment at the Baksan Neutrino Observatory. Eight years of measurement give the result 67.2^+7.2+3.5_-7.0-3.0 solar neutrino units, where the uncertainties are statistical and systematic, respectively. The restrictions these results impose on vacuum neutrino oscillation parameters are given. (c) 1999 The American Physical Society

[en] An intense ³⁷Ar source was produced by the (n, α) reaction on ⁴⁰Ca by irradiating 330 kg of calcium oxide in the fast neutron breeder reactor at Zarechny, Russia. The ³⁷Ar 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 t of gallium metal in the Russian-American solar neutrino experiment SAGE. Ten exposures of the gallium to the source, whose initial strength was ∼ 409 ± 2kCi, were carried out during the period from April to September 2004. The ⁷¹Ge produced by the reaction ⁷¹Ga(ν_e, e^-)⁷¹Ge was extracted, purified, and counted. The measured production rate was 11.0_-0.9^+1.0 (stat.) ±0.6 (syst.) atoms of ⁷¹Ge/d, which is 0.79_-0.10^+0.09 of the theoretically calculated production rate