Nick Jelley

Abstract:

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 N2. 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 α-particles from the decay of 222Rn and its progeny. The overall degassing and concentration efficiency is about 38% and the single-α counting efficiency is approximately 75%. The sensitivity of the radon assay system for D2O is equivalent to ∼ 3 × 10-15 g U/g water. The radon concentration in both the H 2O 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. © 2003 Elsevier B.V. All rights reserved.

Abstract:

Upper limits on the [Formula Presented] flux at the Sudbury Neutrino Observatory have been set based on the [Formula Presented] charged-current reaction on deuterium. The reaction produces a positron and two neutrons in coincidence. This distinctive signature allows a search with very low background for [Formula Presented]’s from the Sun and other potential sources. Both differential and integral limits on the [Formula Presented] flux have been placed in the energy range from 4–14.8 MeV. For an energy-independent [Formula Presented] conversion mechanism, the integral limit on the flux of solar [Formula Presented]’s in the energy range from 4–14.8 MeV is found to be [Formula Presented] (90% C.L.), which corresponds to 0.81% of the standard solar model [Formula presented] [Formula Presented] flux of [Formula Presented], and is consistent with the more sensitive limit from KamLAND in the 8.3–14.8 MeV range of [Formula Presented] (90% C.L.). In the energy range from 4–8 MeV, a search for [Formula Presented]’s is conducted using coincidences in which only the two neutrons are detected. Assuming a [Formula Presented] spectrum for the neutron induced fission of naturally occurring elements, a flux limit of [Formula Presented] (90% C.L.) is obtained. © 2004 The American Physical Society.

Abstract:

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. © 2003 Elsevier Science B.V. All rights reserved.

Abstract:

The Sudbury Neutrino Observatory is a 1000 T D2O Cerenkov detector that is sensitive to B-8 solar neutrinos. The energy, radius, and direction with respect to the sun is Measured for each neutrino event; these distributions are used to separately determine the rates of the charged current, neutral current and electron scattering reactions of neutrinos on deuterium. Assuming an undistorted B-8 spectrum, the nu(e) component of the B-8 solar flux is phi(e) = 1.76(-0.05)(+0.05) (stat.)(-0.09)(+0.09) (syst.) X 10(6) cm(-2)s(-1) based on events with a measured kinetic energy above 5 MeV. The non-nu(e) component is phi(mutau) = 3.41(-0.45)(+0.45)(stat.)(-0.45)(+0.48) (syst.) X 10(6) cm(-2)s(-1), 5.3sigma greater than zero, providing strong evidence for solar nu(e) flavor transformation. The total flux measured with the NC reaction is phi(NC) = 5.09(-0.43)(+0.44) (stat.)(-0.43)(+0.46) (syst.) X 10(6) cm(-2)s(-1), consistent with solar models. The night minus day rate is 14.0% +/- 6.3%(+1.5)(-1.4)% of the average rate. If the total flux of active neutrinos is additionally constrained to have no asymmetry, the nu(e) asymmetry is found to be 7.0% +/- 4.9%(+1.3)(-1.2)%. A global solar neutrino analysis in terms of matter-enhanced oscillations of two active flavors strongly favors the Large Mixing Angle (LMA) solution.