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A radium assay technique using hydrous titanium oxide adsorbent for the Sudbury Neutrino Observatory
Abstract
As photodisintegration of deuterons mimics the disintegration of deuterons by neutrinos, the accurate measurement of the radioactivity from thorium and uranium decay chains in the heavy water in the Sudbury Neutrino Observatory (SNO) is essential for the determination of the total solar neutrino flux. A radium assay technique of the required sensitivity is described that uses hydrous titanium oxide adsorbent on a filtration membrane together with a β−α delayed coincidence counting system. For a assay the detection limit for is a concentration of Th/g water and for of U/g water. Results of assays of both the heavy and light water carried out during the first 2 years of data collection of SNO are presented.
... Average individual radiation exposure from natural and anthropogenic sources 40 Radiation environmental assessments for nuclear installations is required by the authorities. Radionuclides including 3 H, 14 C, 63 Ni, 59 Fe, 89 Sr and 90 Sr and actinides are listed in routine monitoring programs of nuclear power plants and research reactors in many European countries. 14 C released from nuclear power plants is an important contribution in terms of dose to man. ...
... 14 C released from nuclear power plants is an important contribution in terms of dose to man. During decommissioning of nuclear facilities, 3 H, 14 C, 36 Cl, 41 Ca, 55 Fe, 63 Ni, Pu isotopes, 241 Am and 244 Cm are required to be determined for waste characterization and management. ...
... For liquid samples distillation is often used to purify 3 H and 14 C. After distillation, 3 H is collected as condensed tritiated water (HTO) and measured by LSC. In 14 C analysis, Na 2 CO 3 is added to the water sample to enrich 14 C by distilling the sample until near dryness ( 3 H is removed). ...
... Sasaki et al. (1983) described exceptional ion-exchange properties of a synthetic hydrous Ti-dioxide with alkaline earth elements, among others. Later studies allowed the sorption sites to be identified (Venkataramani, 1993) and ultimately found applications in the nuclear industry and research, where specific implementations include radium separation from aqueous solutions (Andersen et al., 2003;Song et al., 2017). ...
The approximate determination of average Ra/U disequilibria in orebodies is one of the most common causes of errors in U reserve estimations. In roll-front deposits, the disequilibria are however frequently distributed following complex geometries, which must be fully understood to prevent major U reserve overestimates and costly unproductive extractive operations. The processes responsible for disruption of the radioactive equilibria and the U and Ra carriers in such complex natural systems remain poorly constrained. In this contribution, we propose an innovative approach, mixing orebody to sub-grain scale studies to unravel the distribution of U and Ra and the processes responsible for their concentration and uncoupling.
Using mineral separations, gamma spectrometry and mineral-chemical analyses, we identified the Fe-Ti clusters (altered ilmenite + pyrite/marcasite) as the microsites for coffinite precipitation and Ra concentration. To understand the influence of such clusters on the distribution of U and Ra at the deposit scale, whole-rock Ra/U disequilibria were measured and mapped at a series of ten drill holes along a profile crosscutting the studied roll-front. The main Ra/U disequilibria are encountered around the mineralization in low U content zones. They are controlled by two main processes. (1) In the oxidized zones, the immobility of 230Th with respect to the U produces patches of Ra disequilibria (carried by the altered U minerals). (2) In the immediate vicinity of the roll-front, the dissolution of the mineralization produces an Ra flux trapped by the alteration products of ilmenites, as definitely confirmed by direct SIMS measurements. Such a process is responsible for the Ra disequilibria envelope located downstream of the richest ores, also known as Ra halo. The highest Ra/U ratios correspond to oxidized upstream samples, but most other high Ra/U ratios are from reduced downstream samples close to the mineralization. Such a low to medium U content envelope with high Ra/U ratios constitutes the main cause of U reserve overestimations.
... Three separate ex-situ methods were developed to measure 224 Ra (pre-cursor of 208 Tl) and 226 Ra (pre-cursor of 214 Bi) and 222 Rn, a possible cause of disequilibrium in the 238 U chain between 226 Ra and 214 Bi. To assay Ra, two independent methods were developed: MnOx [2] and HTiO [3,4]. Due to leaching of trace contaminants in detector materials, Ra and Rn were not in equilibrium with their long-lived parent isotopes. ...
The Sudbury Neutrino Observatory experiment was built to measure the total flux of ⁸B solar neutrinos via the neutral current disintegration deuterium nuclei. This process can be mimiced by daughter isotopes of ²³²Th and ²³⁸U which can photodisintegrate the deuterium nucleus. Measurement of the concentration of such radioisotopes in the heavy water was critical to the success of the experiment. A radium assay technique using Hydrous Titanium Oxide coated filters was developed for this purpose and it was used in conjunction with a delayed beta-alpha coincidence counting system. The design, calibration and operation of this counting system are described in this paper. The counting efficiency for ²³²Th (²²⁴Ra) and ²³⁸U (²²⁶Ra) were measured to be 50 ± 5% and 62 ± 7%
... A feature of QuadraSil-AP is that it can be regenerated with HCl acid, and the metals recovered and analyzed with coincidence beta-alpha counting. This provides a method for ex-situ radioactivity assay for 224 Ra and 226 Ra, as was done in SNO [12]. The method may also allow separate determination for 210 Pb and 210 Bi, to overcome the spectral degeneracy of 210 Bi with CNO neutrinos. ...
A large capacity purification plant and fluid handling system has been constructed for the SNO+ neutrino and double-beta decay experiment, located 6800 feet underground at SNOLAB, Canada. SNO+ is a refurbishment of the SNO detector to fill the acrylic vessel with liquid scintillator based on Linear Alkylbenzene (LAB) and 2 g/L PPO, and also has a phase to load natural tellurium into the scintillator for a double-beta decay experiment with 130Te. The plant includes processes multi-stage dual-stream distillation, column water extraction, steam stripping, and functionalized silica
gel
adsorption columns. The plant also includes systems for preparing the scintillator with PPO and metal-loading the scintillator for double-beta decay exposure. We review the basis of design, the purification principles, specifications for the plant, and the construction and installations. The construction and commissioning status is updated.
Water purification is an important technique in high-mass low radioactivity experiments in modern physics. Water is frequently used both as a shielding and as the sensitive part of a particle detector in underground arrangements, especially in the frame of Astroparticle Physics studies. In this paper, I will describe the main purification techniques and discuss some of its performances.
This review paper provides a summary of the published results of the Sudbury Neutrino Observatory (SNO) experiment that was carried out by an international scientific collaboration with data collected during the period from 1999 to 2006. By using heavy water as a detection medium, the SNO experiment demonstrated clearly that solar electron neutrinos from 8B decay in the solar core change into other active neutrino flavors in transit to Earth. The reaction on deuterium that has equal sensitivity to all active neutrino flavors also provides a very accurate measure of the initial solar flux for comparison with solar models. This review summarizes the results from three phases of solar neutrino detection as well as other physics results obtained from analyses of the SNO data.
In these lectures, I will describe the exciting results that have been obtained by the Sudbury Neutrino Observatory (SNO), after many years of preparation and work. As many people believe, it is often the journey that is most rewarding and the arrival perhaps an anticlimax (perhaps, because the journey was long and eventful) so that I want to show a bit about the journey, the reason for starting on it and the arrival, of course. As we shall see the results from SNO and other neutrino experiments have turned out to be both surprising and exciting, and lead to many new questions about the nature of neutrinos and physics beyond the standard model.
The removal of radioactivity from liquid scintillator has been studied in preparation of a low background phase of KamLAND. This paper describes the methods and techniques developed to measure and efficiently extract radon decay products from liquid scintillator. We report the radio-isotope reduction factors obtained when applying various extraction methods. During this study, distillation was identified as the most efficient method for removing radon-born lead from liquid scintillator. Published by Elsevier B.V.
The PICASSO experiment is starting a new data taking phase. An improved
underground installation has been built and commissioned over the course
of the past year. This article presents the progress made and gives an
outlook for the coming data collection phase and the sensitivity that
can be reached.
PICASSO is a dark matter search experiment that uses the superheated droplet technique to find spin-dependently interacting WIMPs. A set of 1 l detectors with a total active mass of 19.4 g was used to prove the validity of the technique. The data from this run disfavors WIMP-proton cross sections larger than 1.3 pb for a WIMP mass of 29 GeV. Currently phase II of PICASSO is getting started. It will consist of 32 4.5 l detectors with a projected active mass of 2.5 kg and improved detectors.
Solar neutrino experiments have produced a wealth of new information about the properties of neutrinos and about the sun. We present a status report and devote particular attention to new results from the Sudbury Neutrino Observatory. Data obtained over the past two years with salt dissolved in the heavy water to enhance the neutral-current signal have now been analyzed and are presented.
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} eV{sup 2} and {theta}=33.9{sub -2.2}{sup +2.4} degrees.
I describe production and distribution of uncontained sources of 24Na and 222Rn inside the Sudbury Neutrino Observatory (SNO). These unique sources provided a uniquely accurate calibration of the SNO detector of its response to neutrons, produced through photodisintegration of the deuterons in the heavy water target, and to low energy β-Γ decays.
PICASSO (Project in Canada to Search for Supersymmetric Objects) is entering its second experimental phase. A new setup has been installed underground at SNOLAB which will have a total of 2.5kg of active mass. For this a new detector with new purification techniques, new environmental control system and a new data acquisition have been developed. Data taking with the first new detectors has started at the time of the IDM 2006 conference.
Water assay techniques developed for measuring 222Rn, 226Ra and 224Ra in the SNO detector are presented. Recent upgrades to improve the performance of the techniques and to increase the sensitivity to lower levels are discussed.
We describe a very sensitive system for the 222Rn and 226Ra assay of water that we have constructed within the framework of the Borexino solar neutrino experiment. The technique that is applied for 222Rn measurements is based on concentration of radon from water samples followed by gas purification and subsequent alpha counting in low-background miniaturized proportional counters. The same technique is applied to measure the 226Ra concentration by determining the amount of 222Rn in equilibrium with the 226Ra in the water. Sensitivities of ∼1mBq/m3 for 226Ra and ∼100μBq/m3 for 222Rn have been achieved. We present results of measurements illustrating the performance of the system as well as investigations of samples from the Borexino water plant and the shielding water of the Counting Test Facility (CTF, a test facility for the Borexino detector).
The SNO project has now completed two of its three major phases of operation. The no-oscillation hypothesis has been ruled out at 5σ in the pure heavy water phase and 8σ in the salt phase. Discussion in terms of the SeeSaw model is presented.
In the second phase of the Sudbury Neutrino Observatory (SNO), salt was added to the D2O, increasing the sensitivity to measurement of the 8B solar neutrino flux through the neutral current reaction, in which the deuteron is split into its proton and its neutron. This reaction is detected by looking for the Čerenkov light which is produced when the neutron is captured on the salt or on the D2O. In this article, I will describe the in-situ method used for the determination of the neutron background from radioactivity within the D2O, as presented in [1] (see also R.G.H. Robertson's contribution to this conference). This background is, when combined with ex-situ methods, found to be 0.72-0.23+0.24 neutrons per day.
The Sudbury Neutrino Observatory (SNO) has the ability to measure the total and electronic components of the solar neutrino flux, simultaneously, employing independent and complementary techniques. This thesis first introduces the physics of solar neutrinos as well as the mechanism of neutrino oscillation via mixing in the leptonic sector, and possible extensions to the standard model of particle physics. Then the SNO detector is described with a detailed summary of the optical calibration methods. In particular, the extraction of the relative efficiencies of SNO's photomultiplier tubes is relevant towards improvements of the last phase of the SNO experiment, and in the new low energy threshold analysis of the SNO data. The optical calibration in the last phase of the SNO experiment has shown that the detector optics had not been altered compared to previous phases, despite the major changes introduced by the insertion of an array of proportional counters to detect neutrons in SNO. The low energy threshold analysis, that is built on numerous improvements of calibration, simulation, and analysis methods, is then introduced. It leads to the extraction of solar neutrino fluxes, but more importantly, to the measurement of the survival probability and the determination of the oscillation parameters relevant to solar neutrinos. The interpretation of the flux and spectrum results into survival probabilities are obtained from the combined low energy threshold analysis of the data of the pure heavy water and salt phases of the experiment. Especially relevant to our understanding of the neutrinos and the Sun, the survival probability is extracted with two independent parameterizations as a function of neutrino energy. Finally, a novel three-flavor analysis of matter-enhanced oscillation is performed leading to additional information on the neutrino mixing angle [straight theta] 13 that has never been directly investigated with solar neutrino data.
This article provides the complete description of results from the Phase I data set of the Sudbury Neutrino Observatory (SNO). The Phase I data set is based on a 0.65 kiloton-year exposure of 2H2O (in the following denoted as D2O) to the solar 8B neutrino flux. Included here are details of the SNO physics and detector model, evaluations of systematic uncertainties, and estimates of backgrounds. Also discussed are SNO's approach to statistical extraction of the signals from the three neutrino reactions (charged current, neutral current, and elastic scattering) and the results of a search for a day-night asymmetry in the νe flux. Under the assumption that the 8B spectrum is undistorted, the measurements from this phase yield a solar νe flux of ϕ(νe)=1.76-0.05+0.05(stat.)-0.09+0.09(syst.)×106 cm-2 s-1 and a non-νe component of ϕ(νμτ)=3.41-0.45+0.45(stat.)-0.45+0.48(syst.)×106 cm-2 s-1. The sum of these components provides a total flux in excellent agreement with the predictions of standard solar models. The day-night asymmetry in the νe flux is found to be Ae=7.0±4.9(stat.)-1.2+1.3%(syst.), when the asymmetry in the total flux is constrained to be zero.
Results are reported from a joint analysis of Phase I and Phase II data from the Sudbury Neutrino Observatory. The effective electron kinetic energy threshold used is Teff=3.5 MeV, the lowest analysis threshold yet achieved with water Cherenkov detector data. In units of 106 cm-2 s-1, the total flux of active-flavor neutrinos from 8B decay in the Sun measured using the neutral current (NC) reaction of neutrinos on deuterons, with no constraint on the 8B neutrino energy spectrum, is found to be ΦNC=5.140-0.158+0.160(stat)-0.117+0.132(syst). These uncertainties are more than a factor of 2 smaller than previously published results. Also presented are the spectra of recoil electrons from the charged current reaction of neutrinos on deuterons and the elastic scattering of electrons. A fit to the Sudbury Neutrino Observatory data in which the free parameters directly describe the total 8B neutrino flux and the energy-dependent νe survival probability provides a measure of the total 8B neutrino flux Φ8B=5.046-0.152+0.159(stat)-0.123+0.107(syst). Combining these new results with results of all other solar experiments and the KamLAND reactor experiment yields best-fit values of the mixing parameters of θ12=34.06-0.84+1.16 degrees and Δm212=7.59-0.21+0.20×10-5 eV2. The global value of Φ8B is extracted to a precision of -2.95+2.38%. In a three-flavor analysis the best fit value of sin2θ13 is 2.00-1.63+2.09×10-2. This implies an upper bound of sin2θ13<0.057 (95% C.L.).
We describe the R&D on the scintillator purification and assay methods and technology for the SNO+ neutrino and double‐beta decay experiment. The SNO+ experiment is a replacement of the SNO heavy water with liquid scintillator comprised of 2 g∕L PPO in linear alkylbenzene (LAB). During filling the LAB will be transported underground by rail car and purified by multi‐stage distillation and steam stripping at a flow rate of 19 LPM. While the detector is operational the scintillator can be recirculated at 150 LPM (full detector volume in 4 days) to provide repurification as necessary by either water extraction (for Ra, K, Bi) or by functional metal scavenger columns (for Pb, Ra, Bi, Ac, Th) followed by steam stripping to remove noble gases and oxygen (Rn, O2, Kr, Ar). The metal scavenger columns also provide a method for scintillator assay for ex‐situ measurement of the U and Th chain radioactivity. We have developed “natural” radioactive spikes of Pb and Ra in LAB and use these for purification testing. Lastly, we present the planned operating modes and purification strategies and the plant specifications and design.
Remarkable progress has been made over the past 30 years in understanding the flux of neutrinos coming from the sun. The so‐called “solar neutrino puzzle”, whereby the total number of electron neutrinos from the sun does not match the expected total neutrino yield can be now understood in the context of neutrino flavor transformations. The Sudbury Neutrino Observatory has contributed to understanding the solar neutrino problem by measuring both the electron and non‐electron components of the solar neutrino flux. The Sudbury Neutrino Observatory is a 1000 T D2O Cerenkov detector that is sensitive to 8B neutrinos produced in the sun. By using the energy, radius, and direction with respect to the sun, the SNO experiment can separately determine the rates of the charged current, neutral current and electron scattering reactions of neutrinos on deuterium. Assuming an undistorted 8B spectrum, the ve component of the 8B solar flux is ϕe = 1.76−0.05+0.05(stat.)−0.09+0.09 (syst.) × 106 cm−2s−1 based on events with a measured kinetic energy above 5 MeV. The non‐ve component is ϕμτ = 3.41−0.45+0.45(stat.)−0.45+0.48 (syst.) × 106 cm−2s−1, 5.3σ greater than zero, providing strong evidence for solar ve flavor transformation. The total flux measured with the NC reaction is ϕNC = 5.09−0.43+0.44(stat.)−0.43+0.46 (syst.) × 106 cm−2s−1, consistent with the Standard Solar Model. A global solar neutrino analysis in terms of matter‐enhanced oscillations of two active flavors strongly favors the Large Mixing Angle (LMA) solution. © 2003 American Institute of Physics
The solar neutrino problem arose when the first measurements of the flux of neutrinos from the Sun, taken by Raymond Davis, Jr. with a Cl-Ar radiochemical detector, fell substantially below the value predicted theoretically by John Bahcall. Bahcall's prediction came from a detailed model of the nuclear reactions powering the Sun. Resolution of the problem came three decades later with the observation of nonelectron flavors of neutrinos in the solar flux. The use of heavy water in the Sudbury Neutrino Observatory (SNO) experiment provided a means to measure both electron and nonelectron components, and the presence of the latter showed that neutrino flavor conversion was taking place—a hallmark of neutrino oscillation and mass. The solar models were vindicated, and the Standard Model of elementary particles and fields had to be revised. Here we present an account of the SNO project, its conclusions to date, and its ongoing analysis.
A new laboratory for astroparticle physics has been created in the Creighton Mine near Sudbury, Ontario, Canada. The laboratory is located at a great depth to provide shielding from the cosmic-ray backgrounds, and it has been constructed as a clean room to protect experiments from radioactive dust contamination. In this review, we discuss the motivation for the establishment of the laboratory and the design and construction process. We also introduce the initial suite of experiments.
The Sudbury Neutrino Observatory was designed to operate in three distinct configurations that made use of different techniques for measuring the rate of the neutral-current disintegration of deuterium by solar neutrinos. In the third of these phases an array of 3 He-filled proportional counters was deployed in the heavy water, and neutrons from the neutrino-induced breakup of deuterium were detected when they captured on 3 He, liberating 764 keV of energy in the form of ionization of the gas. Aspects of the analysis of the data from this phase are described, and the results presented. There is good agreement with the results obtained with the other techniques in previous phases, and improved precision on the determination of the "solar" mixing angle.
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.
The PICASSO experiment reports an improved limit for the existence of cold dark matter WIMPs interacting via spin-dependent interactions with nuclei. The experiment is installed in the Sudbury Neutrino Observatory at a depth of 2070 m. With superheated C4F10 droplets as the active material, and an exposure of 1.98±0.19 kg day, no evidence for a WIMP signal was found. For a WIMP mass of 29 GeV/c2, limits on the spin-dependent cross section on protons of σp=1.31 pb and on neutrons of σn=21.5 pb have been obtained at 90% C.L. In both cases, some new parameter space in the region of WIMP masses below 20 GeV/c2 has now been ruled out. The results of these measurements are also presented in terms of limits on the effective WIMP-proton and neutron coupling strengths ap and an.
We present results of systematic studies of the radiation response of superheated liquid droplet detectors, which are used in the PICASSO dark matter search experiment. This detection technique is based on the phase transitions of superheated liquid Freon droplets dispersed and trapped in a polymerized gel. Phase transitions can be induced by nuclear recoils following particle interactions and, in particular, interactions with Weakly Interacting Massive Particles (WIMPs). These detectors are threshold devices since a minimal energy deposition is necessary to induce a phase transition and their sensitivity to various types of radiation depends strongly on the operating temperature and pressure. The sensitivity to neutrons, α-particles and γ-rays was determined as a function of these operating parameters and the results are compared with simulations. In particular, we present a complete characterization of the response of detector modules already in use for a dark matter search at the SNO site to detect WIMPs and discuss possible background sources.
The existing hydrous titanium oxide (HTiO) technique for the measurement of 224Ra and 226Ra in the water at the Sudbury Neutrino Observatory (SNO) has been changed to make it faster and less sensitive to trace impurities in the HTiO eluate. Using HTiO-loaded filters followed by cation exchange adsorption and HTiO co-precipitation, Ra isotopes from 200 to 450 tonnes of heavy water can be extracted and concentrated into a single sample of a few millilitres with a total chemical efficiency of 50%. Combined with beta–alpha coincidence counting, this method is capable of measuring of 224Ra and of 226Ra from the 232Th and 238U decay chains, respectively, for a 275 tonne D2O assay, which are equivalent to Th/g and in heavy water.
The technique used at the Sudbury Neutrino Observatory (SNO) to measure the concentration of 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 of H2O or 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 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 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 $^3$He
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 $^8$B solar neutrino flux was largely
independent of the methods employed in previous phases. The total flux of
active neutrinos was measured to be
$5.54^{+0.33}_{-0.31}(stat.)^{+0.36}_{-0.34}(syst.)\times 10^{6}$ 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 $\Delta m^2 = 7.59^{+0.19}_{-0.21}\times 10^{-5}{eV}^2$ and
$\theta = 34.4^{+1.3}_{-1.2}$ degrees.
Four methods for determining the composition of low-level uranium- and
thorium-chain surface contamination are presented. One method is the
observation of Cherenkov light production in water. In two additional methods a
position-sensitive proportional counter surrounding the surface is used to make
both a measurement of the energy spectrum of alpha particle emissions and also
coincidence measurements to derive the thorium-chain content based on the
presence of short-lived isotopes in that decay chain. The fourth method is a
radiochemical technique in which the surface is eluted with a weak acid, the
eluate is concentrated, added to liquid scintillator and assayed by recording
beta-alpha coincidences. These methods were used to characterize two `hotspots'
on the outer surface of one of the He-3 proportional counters in the Neutral
Current Detection array of the Sudbury Neutrino Observatory experiment. The
methods have similar sensitivities, of order tens of ng, to both thorium- and
uranium-chain contamination.
The production and analysis of distributed sources of 24Na and 222Rn in the Sudbury Neutrino Observatory (SNO) are described. These unique sources provided accurate calibrations of the response to neutrons, produced through photodisintegration of the deuterons in the heavy water target, and to low energy betas and gammas. The application of these sources in determining the neutron detection efficiency and response of the 3He proportional counter array, and the characteristics of background Cherenkov light from trace amounts of natural radioactivity is described. Comment: 24 pages, 13 figures
We show that cavitation of a solution of thorium-228 in water does not induce
its transformation at a faster rate than the natural radioactive decay. We
measured the activity of a thorium-228 solution in water before, and after, it
was subjected to a cavitation at 44 kHz and $250 $W for 90 minutes in order to
observe any change in the thorium half-life. The results were compared to the
original activity of the sample and we observed no change. Our results and
conclusions conflict with those in a recent paper by F. Cardone et. al. [Phys.
Lett. A 373 (2009) 1956-1958].
Thesis (Ph. D.)--University of Washington, 2004 The Sudbury Neutrino Observatory (SNO) is capable of detecting electron antineutrinos, n̄e , through the charged-current weak interaction n̄e + d → e+ + n + n denoted as CC. SNO registers electron antineutrino interactions with deuterons, d, via a time coincidence of detector events produced by any of the three product particles. Historically, proposals have suggested conversion of solar electron neutrinos into electron antineutrinos as either a solution to the "solar neutrino problem" or a signature of time-varying neutrino interactions with strong solar magnetic fields. This dissertation introduces the SNO detector via a brief overview of the main scientific objective of the SNO experiment. The potential sources of electron antineutrinos are enumerated and evaluated for their detection potential. The core of the analysis presented here investigates how to maximize SNO's sensitivity to an electron antineutrino signal in the 8B solar neutrino energy range. Backgrounds that can mimic event coincidences similar to the electron antineutrino signal are identified and addressed. Finally, 90% confidence level limits of (FB8 n̄e) D2O ≤ 2.4 x 104 cm-2s -1 and (FB8 n̄e) Salt ≤ 2.8 x 104 cm-2s -1 are set on the solar electron antineutrino flux for the Pure D2O and Salt phases of the SNO experiment, where a 8B energy spectrum is assumed for solar electron antineutrinos. These limits correspond to less than 0.47% and 0.56% of the total standard solar model 8B neutrino flux, respectively.
The 226Ra2+ selectivity of both the self-assembled (iso)-guanosine-based systems and ionizable thiacalix[4]crown dicarboxylic acids was determined in gas-field-produced water and a metal ion-containing model solution (simulant). Seven gas-field-produced water samples have been analyzed. From a sample (K5D) with average metal ion concentrations ([metal(tot)] = 0.14 M), thiacalix[4]crown-5 dicarboxylic acid (10(-4) M) extracts 60% of the 226Ra2+ content. Extractions performed with the model solution ((M)K5D) indicate that in K5D there is significant competition in 226Ra2+ extraction due to the organic constituents of K5D, in particular with self-assembled extractants guanosine and isoguanosine. Nevertheless, all four extractants extract 226Ra2+ both from the produced water K5D and the model solution (M)K5D, even with a 100-fold excess of [metal(tot)] to [extractant]. The extracted 226Ra2+ cations could effectively be stripped from the extractants bywashing with pH 2 water. The results obtained with the extractants used, especially thiacalix[4]crown-5 dicarboxylic acid 3, clearly demonstrate the way to selectively remove Ra2+ from gas-field-produced waters.
Organic extractants play a significant role in the selective removal of radioactive cations from waste streams. Although, literature on the selective removal of man-made radioactive material such as Americium (Am) is widespread, the selective removal of naturally occurring radioactive material such as Ra2+ is only mentioned sporadically. This tutorial review deals with the selective extraction of the highly radiotoxic Ra2+. Special attention is paid to different types of organic extractants used.
The Sudbury Neutrino Observatory (SNO) is capable of measuring simultaneously the flux of electron-type neutrinos and the total flux of all active flavours of neutrinos originating from the Sun. A model-independent test of neutrino flavour transformation was performed by comparing these two measurements. Assuming an undistorted neutrino energy spectrum, this transformation has been definitively demonstrated in the pure D2O phase of the SNO experiment. In the second phase with dissolved NaCl in the D2O, the total active solar neutrino flux was measured without any assumption on the energy dependence of flavour transformation. In this talk, results from these measurements, their physics implications and the current status of the SNO experiment are presented.
The Sudbury Neutrino Observatory (SNO) has precisely determined the total
active (nu_x) 8B solar neutrino flux without assumptions about the energy
dependence of the nu_e survival probability. The measurements were made with
dissolved NaCl in the heavy water to enhance the sensitivity and signature for
neutral-current interactions. The flux is found to be 5.21 +/- 0.27 (stat) +/-
0.38 (syst) x10^6 cm^{-2}s^{-1}, in agreement with previous measurements and
standard solar models. A global analysis of these and other solar and reactor
neutrino results yields Delta m^{2} = 7.1^{+1.2}_{-0.6}x10^{-5} ev^2 and theta
= 32.5^{+2.4}_{-2.3} degrees. Maximal mixing is rejected at the equivalent of
5.4 standard deviations.
The Sudbury Neutrino Observatory (SNO) measures both the flux of the electron-type neutrinos and the total flux of all active flavours of neutrinos originating from the Sun. A model-independent test of neutrino flavour transformation was performed by comparing these two measurements. In 2002, this flavour transformation was definitively demonstrated. In this talk, results from these measurements and the current status of the SNO detector are presented.
PACS: 26.65.+t Solar neutrinos – 14.60.Pq Neutrino mass and mixing – 95.85.Ry Neutrino, muon, pion, and other elementary particles; cosmic rays
The Sudbury Neutrino Observatory (SNO) is a 1000-tonne heavy water Cherenkov detector. Its usage of \dto as target allows the simultaneous measurements of the $\nu_e$ flux from $^8$B decay in the Sun and the total flux of all active neutrino species through the charged-current and the neutral-current interactions on the deuterons. Assuming the standard $^{8}$B shape, the $\nu_e$ component of the $^{8}$B solar neutrino flux is measured to be $\phi_e = 1.76^{+0.05}_{-0.05}{(stat.)}^{+0.09}_{-0.09} {(syst.)} x 10^6 {\rm cm}^{-2} {\rm s}^{-1}$ for a kinetic energy threshold of 5 MeV. The non-\nue component is found to be $\phinumutau = 3.41^{+0.45}_{-0.45}{(stat.)}^{+0.48}_{-0.45} {(syst.)} x 10^6 {\rm cm}^{-2} {\rm s}^{-1}$. This $5.3\sigma$ difference provides strong evidence for $\nu_{e}$ flavor transformation in the solar neutrino sector. The total active neutrino flux is measured with the neutral-current reaction at a neutrino energy threshold of 2.2 MeV. This flux is determined to be $\phi_{NC} = 5.09^{+0.44}_{-0.43}{(stat.)}^{+0.46}_{-0.43} {(syst.)} x 10^6 {\rm cm}^{-2} {\rm s}^{-1}$, and is consistent with solar model predictions. Assuming an undistorted $^8$B spectrum, the night minus day rate is 14.0$\pm$6.3(stat.)$^{+1.5}_{-1.4}$(sys.)\% of the average rate in the charged-current channel. If the total active neutrino flux is constrained to have no asymmetry, the night-day asymmetry in the $\nu_e$ flux is found to be 7.0$\pm$4.9(stat.)$^{+1.3}_{1.2}$(sys.)\%. A global analysis of all the available solar neutrino data in terms of matter-enhanced oscillations of two active flavors strongly favors the Large Mixing Angle (LMA) solution.
The light yield of a water-based Cherenkov detector can be significantly improved by adding a wavelength shifter. Wavelength shifter (WLS) molecules absorb ultraviolet photons and re-emit them at longer wavelengths where typical photomultiplier tubes are more sensitive. In this study, several wavelength shifter compounds are tested for possible deployment in the Sudbury Neutrino Observatory (SNO). Test results on optical properties and chemical compatibility for a few WLS candidates are reported; together with timing and gain measurements. A Monte Carlo simulation of the SNO detector response is used to estimate the total light gain with WLS. Finally, a cosmic ray Cherenkov detector was built to investigate the optical properties of WLS.
Observations of neutral current neutrino interactions on deuterium in the
Sudbury Neutrino Observatory are reported. Using the neutral current, elastic
scattering, and charged current reactions and assuming the standard 8B shape,
the electron-neutrino component of the 8B solar flux is 1.76
+/-0.05(stat.)+/-0.09(syst.) x10^6/(cm^2 s), for a kinetic energy threshold of
5 MeV. The non-electron neutrino component is
3.41+/-0.45(stat.)+0.48,-0.45(syst.) x10^6/(cm^2 s), 5.3 standard deviations
greater than zero, providing strong evidence for solar electron neutrino flavor
transformation. The total flux measured with the NC reaction is 5.09
+0.44,-0.43(stat.)+0.46,-0.43(syst.)x10^6/(cm^2 s), consistent with solar
models.
Study on the adsorption of uranium, dissolved in sea water, on hydrous titanium (N) oxide was carried out and the mechanism of this adsorption was discussed. Hydrous titanium(N) oxide was prepared by the precipitation method from titanium (N) chloride and aqueous ammonia at different temperatures. The amount of OH group on the surface of hydrous titanium(N) oxide crystallites, which was measured by adsorption of fluoride ion, decreased with increasing preparation temperature (Fig. 3). Potassium adsorbed increased linearly with increasing the amount of surface OH group of hydrous titanium (N) oxide. On the other hand, the reverse relation existed between the amount of uranium adsorbed and that of surface OH group (Fig. 7). The enthalpy change (ΔH) was found to be — 3.4kcal/mol and 11. lkcal/mol for the potassium adsorption and the uranium adsorption on hydrous titanium (N) oxide, respectively. These results suggest that the uranium adsorption is accompanied by certain complex reactions.
It is well known that hydrous titanium oxides are useful as an inorganic adsorbent for uranium resources in seawater. In this work, it was found that a characteristic layer structure appears when the Ti-U coprecipitates formed by the addition of aqueous ammonia to the nitric acid/sulfuric acid solution are heated in an 8%H2-92%Ar reducing atmosphere at a relatively low temperature (around 350°C). The formation of this layer structure and the phase transformation which proceeds in air with time were examined by means of X-ray diffraction analysis, magnetic susceptibility measurement, X-ray photoelectron spectroscopy, thermogravimetry etc. These results are considered to suggest that the layer structure is formed by the occupation of uranium (probably as uranyl units) between the layers in the titanium oxide crystal.
Equilibrium adsorption behavior of divalent metal ions onto hydrous titanium (IV) oxide (HTO) was studied. A general equilibrium adsorption equation was derived from three simultaneous equilibrium reactions: (1) hydrolysis of metal ions to the hydroxides, (2) deprotonation of hydroxyl groups (adsorption sites) on HTO's surface and (3) complexation of the hydroxides with the deprotonated sites. The theoretical equilibrium adsorption equation was confirmed by several experimental results under acidic or basic conditions using uranium, lead, cadmium and zinc ions as the adsorbates. It is demonstrated that two parameters within the equation provide information about the adsorption capacity and the selectivity of adsorbent for target metal ions. The HTO employed here had available sites of 7.15 x 10(-4) mol-g-1 for all experiments. Metal ions were adsorbed preferentially on the HTO in the following sequence: Zn2+ < Cd2+ < Pb2+ < UO22+.
The occurrence in the literature of numerous, inconsistent and limited definitions of a detection limit has led to a re-examination of the questions of signal detection and signal extraction in analytical chemistry and nuclear chemistry. Three limiting levels have been defined: LC-the net signal level (instrument response) above which an observed signal may be reliably recognized as "detected"; LD-the "true" net signal level which may be a priori expected to lead to detection; and LQ-the level at which the measurement precision will be satisfactory for quantitative determination. Exact defining equations as well as series of working formulae are presented both for the general analytical case and for radioactivity. The latter, assumed to be governed by the Poisson distribution, is treated in such a manner that accurate limits may be derived for both short- and long-lived radionuclides either in the presence or absence of interference. The principles are illustrated by simple examples of spectrophotometry and radioactivity, and by a more complicated example of activation analysis in which a choice must be made between alternative nuclear reactions.
Hydrous manganese dioxide in a cryptomelane-type showed an excellent ion-exchange selectivity for K/sup +/, Rb/sup +/ and Ba/sup 2 +/ ions having the effective ionic radii of about 1.4 A. Log-log plots of distribution coefficients for alkali and alkaline earth metal ion vs. (HNO/sub 3/) yielded a straight line with a slope of -1 and -2, respectively, indicating the ideal ion-exchange mechanism. The stoichiometry of ion-exchange reactions was also established for the uptake of macro-amounts of alkali metal ions in nitrate media. 50 references 7 figures, 5 tables.
It is well known that hydrous titanium oxides are useful as an inorganic adsorbent for uranium resources in seawater. In this work, it was found that a characteristic layer structure appears when the Ti-U coprecipitates formed by the addition of aqueous ammonia to the nitric acid/sulfuric acid solution are heated in an 8%H2-92%Ar reducing atmosphere at a relatively low temperature (around 350°C). The formation of this layer structure and the phase transformation which proceeds in air with time were examined by means of X-ray diffraction analysis, magnetic susceptibility measurement, X-ray photoelectron spectroscopy, thermogravimetry etc. These results are considered to suggest that the layer structure is formed by the occupation of uranium (probably as uranyl units) between the layers in the titanium oxide crystal.
Sorption sites present on variously prepared amorphous hydrous titanium and thorium oxides (HTiO and HThO, respectively) have been characterized by analyzing the water sorption isotherms of these hydrous oxides using the D'Arcy and Watt equation. Two types of OH groups have been identified as sorption sites on HTiO: one very strong, doubly bonded to Ti atoms (Ti-OH-Ti) and capable of taking part in ion exchange and the other, singly bonded to Ti (Ti-OH), acting only as a water sorption site. Cation exchange (with Na+, for example) with OH groups on HTiO can take place up to a maximum Na/Ti ratio of 0.5. The Na+ present in HTiO hydrates to the same extent as Na+ present in organic ion exchange resins. On HThO, only one type of OH group, acting as a water sorption site, exists. Maxima of about 1.2 sites/Ti on HTiO and 1.5 sites/Th on HThO are strong sorption sites. The interaction of OH groups with sorbed water is nearly the same for both acidic (HTiO) and basic (HThO) hydrous oxides.
A combination of techniques, including AES, SIMS, FTIR, and hydrogen chemisorption, has been used to investigate the activation of nickel ions supported on hydrous titanium oxide (HTO) ion-exchange materials. HTO supports allow metal ions to be loaded via ion exchange such that atomic dispersion is attained in the as-prepared material, even for high metal loadings. The results presented here support earlier work indicating that nickel forms large, 10-20-nm particles during hydrogen reduction of Ni/HTO at temperatures of 300[degree]C of greater. During reduction, these particles become covered by an amorphous film which inhibits catalytic activity. Evidence is presented which supports the theory that this film is composed of carbonaceous residue which originates from the organometallic precursors and organic solvents used to synthesize the HTO support. Reduction/oxidation cycles result in oscillations in the nickel surface concentration which are attributed to decoration of the particles by partially reduced TiO[sub x] species, in a manner similar to a strong metal-support interaction (SMSI). This SMSI occurs at temperatures as low as 300[degree]C, well below the temperatures typically required to induce SMSI on crystalline titania supports. 42 refs., 9 figs., 1 tab.
An advantageous method of determining the uranium and the thorium series content of natural samples is described and assessed. This novel application of coincidence counting to natural dosimetry could be use in a range of studies of geological and archaeological materials, including thermoluminescence and related dating processes.
The Sudbury Neutrino Observatory is a second-generation water Cherenkov detector designed to determine whether the currently observed solar neutrino deficit is a result of neutrino oscillations. The detector is unique in its use of D2O as a detection medium, permitting it to make a solar model-independent test of the neutrino oscillation hypothesis by comparison of the charged- and neutral-current interaction rates. In this paper the physical properties, construction, and preliminary operation of the Sudbury Neutrino Observatory are described. Data and predicted operating parameters are provided whenever possible.
Accurate, quantitative determinations of alpha emitting nuclides by conventional plate counting methods are difficult, because of sample self-absorption problems in counting and because of non-reproducible losses in conventional sample separation methods. Liquid scintillation alpha spectrometry offers an attractive alternative with no sample self-absorption or geometry problems and with 100% counting efficiency. Sample preparation may include extraction of the alpha emitter of interest by a specific organic phase-soluble compound directly into the liquid scintillation counting medium. Detection electronics use energy and pulse-shape discrimination, to yield alpha spectra without beta and gamma background interference. Specific procedures have been developed for gross alpha, uranium, plutonium, thorium and polonium assay. Possibilities for a large number of other applications exist. Accuracy and reproducibility are typically in the 1% range. Backgrounds of the order of 0.01 cpm are readily achievable. The paper will present an overview of liquid scintillation alpha counting techniques and some of the results achieved for specific applications.
The comparison of the predicted and measured fluxes of neutrinos from the sun has now been carried out by four independent experiments. All four have seen a deficit between the rate measured and the rate predicted from complex, iterative models of the sun. This Solar Neutrino Problem has been a source of interest for around 20 years, with possible explainations ranging from astrophysics to new particle physics. The Sudbury Neutrino Observatory (SNO) aims to resolve the problem by the direct comparison of the flux of electron neutrinos to the flux of all flavours of neutrinos, and hence check various models which suggest that the neutrinos are oscillating from electron to muon or tau flavour on their passage from the core of the sun to the earth. SNO itself is a 1 kilo-tonne heavy water Cerenkov detector, which can measure the electron neutrino flux by the break-up of deuterium via a W boson, the CC reaction; and can measure the flux of all neutrinos with the weak disintegration of the deuteron via a Z boson, the NC reaction. In order to make the comparison between the two channels, the backgrounds on each channel must be very well known. The main sources of background are the long lived isotopes of thorium and uranium, and their subsequent decay chains, and to a lesser extent (40)K. The cleanliness requirements for the detector have meant that new regimes of contamination have had to be considered, and new techniques for assay developed. In order to assay to the levels required, new counters have been developed by the author which use the fast beta-alpha coincidences at the ends of the uranium and thorium chains. The counters have a high efficiency, source/counter separation, and at present have a low enough background to assay the heavy water in SNO to the required levels. The development of these counters has gone hand-in-hand with the investigation and calibration of the ion extraction process, seeded ultra-filtration, at the low levels required.
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