[en] We describe a method to measure the concentration of ²²⁴Ra and ²²⁶Ra in the heavy water target used to detect solar neutrinos at the Sudbury Neutrino Observatory and in the surrounding light water shielding. A water volume of 50-400 m³ from the detector is passed through columns which contain beads coated with a compound of manganese oxide onto which the Ra dissolved in the water is adsorbed. The columns are removed, dried, and mounted below an electrostatic chamber into which the Rn from the decay of trapped Ra is continuously flowed by a stream of N₂ gas. The subsequent decay of Rn gives charged Po ions which are swept by the electric field onto a solid-state α counter. The content of Ra in the water is inferred from the measured decay rates of ²¹²Po, ²¹⁴Po, ²¹⁶Po, and ²¹⁸Po. The Ra extraction efficiency is >95%, the counting efficiency is 24% for ²¹⁴Po and 6% for ²¹⁶Po, and the method can detect a few atoms of ²²⁴Ra per m³ and a few tens of thousands of atoms of ²²⁶Ra per m³. Converted to equivalent equilibrium values of the topmost elements of the natural radioactive chains, the detection limit in a single assay is a few times 10^-16 g Th or U/cm³. The results of some typical assays are presented and the contributions to the systematic error are discussed

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[en] The Sudbury Neutrino Observatory (SNO) is a water imaging Cherenkov detector. Its usage of 1000 metric tons of D₂O as target allows the SNO detector to make a solar-model independent test of the neutrino oscillation hypothesis by simultaneously measuring the solar ν_e flux and the total flux of all active neutrino species. Solar neutrinos from the decay of ⁸B have been detected at SNO by the charged-current (CC) interaction on the deuteron and by the elastic scattering (ES) of electrons. While the CC reaction is sensitive exclusively to ν_e, the ES reaction also has a small sensitivity to ν_μ and ν_τ. In this paper, recent solar neutrino results from the SNO experiment are presented. It is demonstrated that the solar flux from ⁸B decay as measured from the ES reaction rate under the no-oscillation assumption is consistent with the high precision ES measurement by the Super-Kamiokande experiment. The ν_e flux deduced from the CC reaction rate in SNO differs from the Super-Kamiokande ES results by 3.3σ. This is evidence for an active neutrino component, in additional to ν_e, in the solar neutrino flux. These results also allow the first experimental determination of the total active ⁸B neutrino flux from the Sun, and is found to be in good agreement with solar model predictions

[en] The Sudbury Neutrino Observatory (SNO) has precisely determined the total active (v_x)⁸B solar neutrino flux without assumptions about the energy dependence of the v_e survival probability. The measurements were made with dissolved NaCl in the heavy water to enhance the sensitivity and signature for neutral-current interactions. The flux is found to be 5.21+-0.27 (stat)+-0.38(syst)x10^-6 cm^-2s^-1, in agreement with previous measurements and standard solar models. A global analysis of these and other solar and reactor neutrino results yields Δm² = 7.1^+1.2_-0.6 x 10^-5 eV² and θ 32.5^+2.4_-2.3 degrees. Maximal mixing is rejected at the equivalent of 5.4 standard deviations

[en] The Sudbury Neutrino Observatory is a second-generation water Cherenkov detector designed to determine whether the currently observed solar neutrino deficit is a result of neutrino oscillations. The detector is unique in its use of D₂O as a detection medium, permitting it to make a solar model-independent test of the neutrino oscillation hypothesis by comparison of the charged- and neutral-current interaction rates. In this paper the physical properties, construction, and preliminary operation of the Sudbury Neutrino Observatory are described. Data and predicted operating parameters are provided whenever possible