Measurement of dissolved in water at the Sudbury Neutrino Observatory

• DOI: 10.1016/j.nima.2003.10.103
• Publication Date: 2003-12-09T11:55:53Z
• Authors: I Blevis; J Boger; E Bonvin; B.T Cleveland; X Dai; F Dalnoki-Veress; G Doucas; J Farine; H Fergani; D Grant; R.L Hahn; A.S Hamer; C.K Hargrove; H Heron; P Jagam; N.A Jelley; C Jillings; A.B Knox; H.W Lee; I Levine; M Liu; S Majerus; A McDonald; K McFarlane; C Mifflin; A.J Noble; S Noël; V.M Novikov; J.K Rowley; M Shatkay; J.J Simpson; D Sinclair; B Sur; J.-X Wang; M Yeh; X Zhu
• Keywords: Heavy water

The technique used at the Sudbury Neutrino Observatory (SNO) to measure the concentration of 222Rn in water is described. Water from the SNO detector is passed through a vacuum degasser (in the light water system) or a membrane contact degasser (in the heavy water system) where dissolved gases, including radon, are liberated. The degasser is connected to a vacuum system which collects the radon on a cold trap and removes most other gases, such as water vapor and nitrogen. After roughly 0.5 tonnes of H2O or 6 tonnes of D2O have been sampled, the accumulated radon is transferred to a Lucas cell. The cell is mounted on a photomultiplier tube which detects the alpha particles from the decay of 222Rn and its daughters. The overall degassing and concentration efficiency is about 38% and the single-alpha counting efficiency is approximately 75%. The sensitivity of the radon assay system for D2O is equivalent to ~3 E(-15) g U/g water. The radon concentration in both the H2O and D2O is sufficiently low that the rate of background events from U-chain elements is a small fraction of the interaction rate of solar neutrinos by the neutral current reaction.<br/>14 pages, 6 figures; v2 has very minor changes<br/>