An array of low-background 3He proportional counters for the Sudbury Neutrino Observatory
2008
An array of
Neutral-CurrentDetectors (NCDs) has been built in order to make a unique measurement of the total active ux of
solar neutrinosin the
Sudbury Neutrino Observatory(SNO). Data in the
third phaseof the SNO experiment were collected between November 2004 and November 2006, after the NCD array was added to improve the
neutral-currentsensitivity of the SNO detector. This array consisted of 36 strings of
proportional counterslled with a mixture of 3He and CF4 gas capable of detecting the neutrons liberated by the neutrino-deuteron
neutral currentreaction in the D2O, and four strings lled with a mixture of 4He and CF4 gas for background measurements. The
proportional counterdiameter is 5 cm. The total deployed array length was 398 m. The SNO NCD array is the lowest-radioactivity large array of
proportional countersever produced. This article describes the design, construction, deployment, and characterization of the NCD array, discusses the electronics and data acquisition system, and considers event signatures and backgrounds.
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