An array of low-background 3He proportional counters for the Sudbury Neutrino Observatory

Center for Experimental Nuclear Physics and Astrophysics, and Department of Physics, University of Washington, Seattle, WA 98195, USA; Los Alamos National Laboratory, Los Alamos, NM 87545, USA; Department of Physics, University of Oxford, Oxford, OX1 3RH, UK; Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA; Department of Physics, Queen's University, Kingston, Ont., Canada K7L 3N6; Department of Physics, University of Texas at Austin, Austin, TX 78712, USA; Physics Department, University of Guelph, Guelph, Ont., Canada N1G 2W1; SNOLAB, Lively, Ont., Canada P3Y 1M3; Institute for Nuclear and Particle Astrophysics, and Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada V6T 1Z1
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 06/2007; DOI: 10.1016/j.nima.2007.05.321
Source: arXiv

ABSTRACT An array of Neutral-Current Detectors (NCDs) has been built in order to make a unique measurement of the total active flux of solar neutrinos in the Sudbury Neutrino Observatory (SNO). Data in the third phase of the SNO experiment were collected between November 2004 and 2006, after the NCD array was added to improve the neutral-current sensitivity of the SNO detector. This array consisted of 36 strings of proportional counters filled with a mixture of 3He and CF4 gas capable of detecting the neutrons liberated by the neutrino-deuteron neutral-current reaction in the D2O, and four strings filled with a mixture of 4He and CF4 gas for background measurements. The proportional counter diameter is 5 cm. The total deployed array length was 398 m. The SNO NCD array is the lowest-radioactivity large array of proportional counters ever 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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