Search

The Sudbury Neutrino Observatory is a 1000 T D 2 O Cerenkov detector that is sensitive to 8 B 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 8 B spectrum, the ν e component of the 8 B solar flux is φ e = 1.76 +0.05 −0.05 (stat.) +0.09 −0.09 (syst.) × 10 6 cm −2 s −1 based on events with a measured kinetic enegy above 5 MeV. The non- ν e component is φ μτ = 3.41 +0.45 −0.45 (stat.) +0.48 −0.45 (syst.) × 10 6 cm −2 s −1 , 5.3 σ greater than zero, providing strong evidence for solar ν e flavor transformation. The total flux measured with the NC reaction is φ NC = 5.09 +0.044 −0.43 (stat.) +0.46 −0.43 (syst.) × 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 ν e asymmetry is found to be 7.0% ± 4.9% +1.3 −1.2 %. A global solar neutrino analysis is terms of matter-enhanced oscillations of two active flavors strongly favors the Large Mixing Angle (LMA) solution.

The technique used at the Sudbury Neutrino Observatory (SNO) to measure the concentration of 222 Rn 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 222 Rn 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 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.

We report results from a combined analysis of solar neutrino data from all phases of the Sudbury Neutrino Observatory. By exploiting particle identification information obtained from the proportional counters installed during the third phase, this analysis improved background rejection in that phase of the experiment. The combined analysis resulted in a total flux of active neutrino flavors from 8B decays in the Sun of (5.25 \pm 0.16(stat.)+0.11-0.13(syst.))\times10^6 cm^{-2}s^{-1}. A two-flavor neutrino oscillation analysis yielded \Deltam^2_{21} = (5.6^{+1.9}_{-1.4})\times10^{-5} eV^2 and tan^2{\theta}_{12}= 0.427^{+0.033}_{-0.029}. A three-flavor neutrino oscillation analysis combining this result with results of all other solar neutrino experiments and the KamLAND experiment yielded \Deltam^2_{21} = (7.41^{+0.21}_{-0.19})\times10^{-5} eV^2, tan^2{\theta}_{12} = 0.446^{+0.030}_{-0.029}, and sin^2{\theta}_{13} = (2.5^{+1.8}_{-1.5})\times10^{-2}. This implied an upper bound of sin^2{\theta}_{13} < 0.053 at the 95% confidence level (C.L.).

This paper details the solar neutrino analysis of the 385.17-day phase-III data set acquired by the Sudbury Neutrino Observatory (SNO). An array of He-3 proportional counters was installed in the heavy-water target to measure precisely the rate of neutrino-deuteron neutral-current interactions. This technique to determine the total active B-8 solar neutrino flux was largely independent of the methods employed in previous phases. The total flux of active neutrinos was measured to be 5.54(-0.31)(+0.33)(stat.)(-0.34)(+0.36)(syst.) x 10(6) cm(-2) s(-1), consistent with previous measurements and standard solar models. A global analysis of solar and reactor neutrino mixing parameters yielded the best-fit values of Delta m(2) = 7.59(-0.21)(+0.19) x 10(-5) eV(2) and theta = 34.4(-1.2)(+1.3) degrees. DOI: 10.1103/PhysRevC.87.015502

Measurements have been made of the thorium, uranium and potassium concentrations in a variety of materials. The methods of direct γ-ray counting and neutron activation analysis have been employed, and cases of secular disequilibrium most notably in aluminum have been identified. Several comprehensive tables of results are provided.

The experimental evidence of a distortion in the β-spectra of 3H, 35S, 63Ni, 14C and IBEC-spectrum of 71Ge is reviewed. The distortions seen in the five nuclei are consistent with their interpretation as the signal of the emission of a neutrino of 17-keV mass and mixing angle of 0.1. Some of the implications of this discovery are reviewed.

Results are reported on the measurement of the atmospheric neutrino-induced muon flux at a depth of 2 kilometers below the Earth's surface from 1229 days of operation of the Sudbury Neutrino Observatory (SNO). By measuring the flux of through-going muons as a function of zenith angle, the SNO experiment can distinguish between the oscillated and un-oscillated portion of the neutrino flux. A total of 514 muon-like events are measured between $-1 \le \cos{\theta}_{\rm zenith} \le 0.4$ in a total exposure of 2.30\times 10^{14}$ cm$^{2}$ s. The measured flux normalization is $1.22 \pm 0.09$ times the Bartol three-dimensional flux prediction. This is the first measurement of the neutrino-induced flux where neutrino oscillations are minimized. The zenith distribution is consistent with previously measured atmospheric neutrino oscillation parameters. The cosmic ray muon flux at SNO with zenith angle $\cos{\theta}_{\rm zenith} > 0.4$ is measured to be $(3.31 \pm 0.01 {\rm (stat.)} \pm 0.09 {\rm (sys.)}) \times 10^{-10}~\mu$/s/cm$^{2}$., Comment: 17 pages, 11 figures

It is suggested that the late neutrino events from supernova SN 1987 A detected by the Kamiokande and IMB detectors can be understood as arising from massive neutrinos decaying in flight. If the neutrino mass is 17 keV, the estimated mean life is (0.6–1.6) x 10 4 s. The shorter prompt pulse then implies an upper limit to the mass of the lightest neutrino of 13 eV.

This article provides the complete description of resultsfrom the Phase I data set of the Sudbury Neutrino Observatory (SNO). ThePhase I data set is based on a 0.65 kt-year exposure of heavy water tothe solar 8B neutrino flux. Included here are details of the SNO physicsand detector model, evaluations of systematic uncertainties, andestimates of backgrounds. Also discussed are SNO's approach tostatistical extraction of the signals from the three neutrino reactions(charged current, neutral current, and elastic scattering) and theresults of a search for a day-night asymmetry in the ?e flux. Under theassumption that the 8B spectrum is undistorted, the measurements fromthis phase yield a solar ?e flux of ?(?e) =1.76+0.05?0.05(stat.)+0.09?0.09 (syst.) x 106 cm?2 s?1, and a non-?ecomponent ?(? mu) = 3.41+0.45?0.45(stat.)+0.48?0.45 (syst.) x 106 cm?2s?1. The sum of these components provides a total flux in excellentagreement with the predictions of Standard Solar Models. The day-nightasymmetry in the ?e flux is found to be Ae = 7.0 +- 4.9 (stat.)+1.3?1.2percent (sys.), when the asymmetry in the total flux is constrained to bezero.

Results are reported from the complete salt phase of the Sudbury Neutrino Observatory experiment in which NaCl was dissolved in the {sup 2}H{sub 2}O (''D{sub 2}O'') target. The addition of salt enhanced the signal from neutron capture as compared to the pure D{sub 2}O detector. By making a statistical separation of charged-current events from other types based on event-isotropy criteria, the effective electron recoil energy spectrum has been extracted. In units of 10{sup 6}cm{sup -2}s{sup -1}, the total flux of active-flavor neutrinos from {sup 8}B decay in the Sun is found to be 4.94{sub -0.21}{sup +0.21}(stat){sub -0.34}{sup +0.38}(syst) and the integral flux of electron neutrinos for an undistorted {sup 8}B spectrum is 1.68{sub -0.06}{sup +0.06}(stat){sub -0.09}{sup +0.08}(syst); the signal from ({nu}{sub x},e) elastic scattering is equivalent to an electron-neutrino flux of 2.35{sub -0.22}{sup +0.22}(stat){sub -0.15}{sup +0.15}(syst). These results are consistent with those expected for neutrino oscillations with the so-called large mixing angle parameters and also with an undistorted spectrum. A search for matter-enhancement effects in the Earth through a possible day-night asymmetry in the charged-current integral rate is consistent with no asymmetry. Including results from other experiments, the best-fit values for two-neutrino mixing parameters are {delta}m{sup 2}=(8.0{sub -0.4}{sup +0.6})x10{sup -5}more » eV{sup 2} and {theta}=33.9{sub -2.2}{sup +2.4} degrees.« less

A search has been made for sinusoidal periodic variations in the 8B solar neutrino flux using data collected by the Sudbury Neutrino Observatory over a 4-year time interval. The variation at a period of 1 yr is consistent with modulation of the 8B neutrino flux by the Earth's orbital eccentricity. No significant sinusoidal periodicities are found with periods between 1 d and 10 years with either an unbinned maximum likelihood analysis or a Lomb-Scargle periodogram analysis. The data are inconsistent with the hypothesis that the results of the recent analysis by Sturrock et al., based on elastic scattering events in Super-Kamiokande, can be attributed to a 7% sinusoidal modulation of the total 8B neutrino flux.

Upper limits on the \nuebar flux at the Sudbury Neutrino Observatory have been set based on the \nuebar 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 \nuebar's from the Sun and other potential sources. Both differential and integral limits on the \nuebar flux have been placed in the energy range from 4 -- 14.8 MeV. For an energy-independent ��_e --> \nuebar conversion mechanism, the integral limit on the flux of solar \nuebar's in the energy range from 4 -- 14.8 MeV is found to be ��_\nuebar, submitted to Phys. Rev. D

A calibration source employing 8Li (t_1/2 = 0.838s) has been developed for use with the Sudbury Neutrino Observatory (SNO). This source creates a spectrum of beta particles with an energy range similar to that of the SNO 8B solar neutrino signal. The source is used to test the SNO detector's energy response, position reconstruction and data reduction algorithms. The 8Li isotope is created using a deuterium-tritium neutron generator in conjunction with a 11B target, and is carried to a decay chamber using a gas/aerosol transport system. The decay chamber detects prompt alpha particles by gas scintillation in coincidence with the beta particles which exit through a thin stainless steel wall. A description is given of the production, transport, and tagging techniques along with a discussion of the performance and application of the source., 11 pages plus 9 figures, Sumbitted to Nuclear Instruments and Methods A

The reaction $^{32}\mathrm{S}(^{14}\mathrm{N}, \mathrm{pn}\ensuremath{\gamma})^{44}\mathrm{Ti}$ has been studied with a view to populating high spin states in $^{44}\mathrm{Ti}$. In singles and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence experiments $\ensuremath{\gamma}$-ray transitions in the ground state band and a negative parity band are seen and three levels connected to the ground state band, at 6508, 7671, and 8040 keV, are inferred. Angular distributions are consistent with stretched cascades. The lifetime of the 7671-keV level, presumed ${10}^{+}$, has been determined by the attenuated Doppler-shift method to be 2.7 \ifmmode\pm\else\textpm\fi{} 0.5 ps. A comparison of the present reaction with the recently reported $^{28}\mathrm{Si}(^{19}\mathrm{F}, p2n\ensuremath{\gamma})^{44}\mathrm{Ti}$ reaction is made and a method for predicting the propensity of these types of reaction to feed high spin states is proposed. $\mathrm{An}{(\mathrm{fp})}^{4}$ shell model calculation of yrast levels up to $J=12$ has been made.

A reported splitting of the lowest T = 2 strength in /sup 44/Ti has been confirmed by examining resonances in the /sup 40/Ca(..cap alpha.., ..gamma..) /sup 44/Ti reaction at excitation energies in the region of 9.28--9.36 MeV. A level at 9298 +- 2 keV in /sup 44/Ti is found to have ..gamma..-decays to the 1/sup +/, T = 1 level at 7216 keV and to a T = 0 level at 3756 keV. The former transition is attributed to a T = 2 component in the 9298 keV level, with, however, the main T = 2 strength remaining in the level at 9338 +- 2 keV, as reported previously. Evidence is presented for a weak (9338 ..-->.. 3756), ..delta..T = 2 transition in addition to the dominant (9338 ..-->.. 7216), ..delta..T = 1 ..gamma..-decay branch. The two levels at 9298 and 9338 keV are interpreted as an isospin-mixed doublet. The perturbing matrix element is estimated to be 16 +- 3 keV, and the unperturbed T = 2 state to lie at 9330 +- 4 keV.

Evidence on the lifetimes and spins of the bound levels of /sup 44/Ti as obtained from the /sup 40/Ca(..cap alpha..,..gamma..)/sup 44/Ti reaction is presented. Lifetimes were obtained by the Doppler shift attenuation method, and spins from angular distribution and transition strength arguments. Weak ..gamma..-ray branches have been established in ..gamma..-..gamma.. coincidences between Ge(Li) and NaI(Tl) detectors. Present information supports the interpretation of most of the bound levels of /sup 44/Ti in terms of rotational-like bands.

The observation of the following three reactions: νed→ppe; νxe→νxe; and νxd→νxpn (where νx is any left- handed neutrino) in a heavy water Cerenkov detector which is being designed, allows the solar 8B ve flux, spectrum and direction to be measured. In addition, the total solar 8 Bν c neutrino flux, direction and integral spectrum, independent of neutrino flavor, may be determined to provide several independent methods to resolve the solar neutrino problem.

The extrapolated end-point of the tritium beta spectrum has been measured in a tritium-implanted Si(Li) detector for which the radiation damage has been kept small. The result is 18577 +- 7 eV. Adding the maximum recoil energy, the /sup 3/H-/sup 3/He atomic mass difference is taken to be 18580 +- 7 eV.

A detailed study of the events recorded with a 208 cm 3 intrinsic germanium γ-ray detector produced by interactions of natural environmental radiation was undertaken. In the first part of this work, the data on events from characteristic radioactivity are analysed to optimise the shielding requirements for reducing the γ-ray background as seen by the detector. A thickness of 15 cm of Pb all around the detector in the laboratory location, or only 5 cm in the underground location at the mine, is found to be sufficient to attenuate the event rates from environmental characteristic γ-rays to less than the event rates from intrinsic contamination of the detector components in the detector assembly. The salt mine is found to be a natural environment low in γ-ray background.

A γ-ray spectrometer with three large HpGe crystals totalling 560 cm 3 in one cryostat was fabricated with a view to achieving ultralow background count rates in the energy region below 4 MeV. At 2 MeV, the continuum background is 1.7 × 10 −3 counts per keV per 1000 h per cm 3 , making this one of the lowest background, large systems at the present time. Only passive shielding is used. Residual activities intrinsic to the detector and shielding materials have been identified with respect to their origin from fission and cosmogenic sources.

The available evidence on the spin-parity assignments for the 3176 and 3646 keV levels of 44 Ti is reviewed. The results of new studies of the decay γ-rays of the 4.22 MeV resonance in the 40 Ca(α, γ) 44 Ti reaction are presented. Angular distribution fits and strength arguments are used to establish J (3176) = 3 and J (3646) = 4, with the two levels having the same parity. If the 46 Ti(p, t) 44 Ti reaction excites only states of natural parity, then J π (3176) = 3 − and J π (3646) = 4 − .

A formalism is presented for extracting isospin mixing in the compound nucleus from a comparison of Ericson fluctuations in the cross section of mirror reactions. Some experimental aspects of the comparison are also discussed.

Gamma-ray and charged-particle emission has been studied after bombardment of 58 Ni with 16 O at energies from 44.5–76.5 MeV. The excitation functions for various reaction channels have been measured. The locus in energy and spin of maximum cross section (the entry line) of the γ-emitting region in the 2pγ and 3pγ channels have been studied through measurement of γ-ray multiplicity, average particle energy and average γ-ray energy. The standard deviations in both energy and spin of the distributions of cross section are presented. Statistical model calculations including shell corrections in the level density show very satisfactory agreement with the experimental results. The moment of inertia at high spin and excitation energy is deduced from the measured entry line.

The decay of /sup 50/V has been studied with a low-background, three-crystal intrinsic Ge detector operating in a salt mine. The partial half-life for electron-capture decay to the first excited state of /sup 50/Ti has been estimated to be (2.05+-0.49)/times/10/sup 17/ yr, and the partial half-life for ..beta../sup /minus// decay to the first excited state of /sup 50/Cr has been estimated to be (8.2/sub /minus/3.1//sup +13.1/)/times/10/sup 17/ yr.

The half-life of tritium implanted into a Si(Li) x-ray detector has been determined to be 12.32\ifmmode\pm\else\textpm\fi{}0.03 yr by following the decay for about 5.5 years. Using a recently determined \ensuremath{\beta}-decay end-point energy for the same system, the product (${G}_{A}$/${G}_{V}$)〈\ensuremath{\sigma}\ensuremath{\tau}〉 for tritium has been determined to be 2.094\ifmmode\pm\else\textpm\fi{}0.004.

An upper limit of 0.16% (one standard deviation) is placed on the $\ensuremath{\gamma}$-ray branching ratio for the $\ensuremath{\Delta}T=2$ transition from the $T=2, {0}^{+}$ level at 9338 \ifmmode\pm\else\textpm\fi{} 2 keV in $^{44}\mathrm{Ti}$ to the first excited ${2}^{+}$ level at 1083 keV. A new determination of $\frac{{\ensuremath{\Gamma}}_{\ensuremath{\alpha}}{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}}{\ensuremath{\Gamma}}$ for the $T=2$ level gives 0.24 eV. The upper limit for the $\ensuremath{\Delta}T=2$ transition is shown to be consistent with shell-model estimates of isospin mixing.

It is pointed out that present lower bounds on the lifetime for neutrinoless double β-decay put stringent upper limits on the mixing of a heavy Majorana neutrino (< a few MeV) with the dominantly coupled light neutrino of β-decay.

A \ensuremath{\gamma}-ray peak attributed to the deexcitation of the first excited state of $^{50}\mathrm{Ti}$ has been detected from vanadium metal by a large, low background intrinsic Ge detector operating in a salt mine. The partial half-life for the electron capture decay of $^{50}\mathrm{V}$ to the first excited state of $^{50}\mathrm{Ti}$ has been estimated to be ${1.2}_{\mathrm{\ensuremath{-}}0.4}^{+0.8}$\ifmmode\times\else\texttimes\fi{}${10}^{17}$ yr. A limit on the partial half-life for ${\ensuremath{\beta}}^{\mathrm{\ensuremath{-}}}$ decay is also obtained.

It is shown that there is a threshold 17 keV below the end point of the β spectrum of 35 S in the published work of Ohio et al. The distortion of the Kurie plot is consistent with that seen in the 3 H β spectrum, strengthening the earlier suggestion that the distortion is due to the emission of a neutrino of mass 17 keV.

The /sup 12/C(/sup 12/C,t)/sup 21/Na reaction has been studied at theta = 0/sup 0/ over an energy range from 37 to 50 MeV. Rapid fluctuations in the cross sections to individual final states were observed, but no conclusive evidence for pronounced resonant structure was observed, either at the 19.3 MeV (c.m.) anomaly or elsewhere.