53 research outputs found
Measurement of 222Rn dissolved in water at the Sudbury Neutrino Observatory
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.Comment: 14 pages, 6 figures; v2 has very minor change
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Cosmogenic neutron production at the Sudbury Neutrino Observatory
Neutrons produced in nuclear interactions initiated by cosmic-ray muons present an irreducible background to many rare-event searches, even in detectors located deep underground. Models for the production of these neutrons have been tested against previous experimental data, but the extrapolation to deeper sites is not well understood. Here we report results from an analysis of cosmogenically produced neutrons at the Sudbury Neutrino Observatory. A specific set of observables are presented, which can be used to benchmark the validity of geant4 physics models. In addition, the cosmogenic neutron yield, in units of 10-4 cm2/(g·μ), is measured to be 7.28±0.09(stat)-1.12+1.59(syst) in pure heavy water and 7.30±0.07(stat)-1.02+1.40(syst) in NaCl-loaded heavy water. These results provide unique insights into this potential background source for experiments at SNOLAB
Constraints on Nucleon Decay via "Invisible" Modes from the Sudbury Neutrino Observatory
Data from the Sudbury Neutrino Observatory have been used to constrain the
lifetime for nucleon decay to ``invisible'' modes, such as n -> 3 nu. The
analysis was based on a search for gamma-rays from the de-excitation of the
residual nucleus that would result from the disappearance of either a proton or
neutron from O16. A limit of tau_inv > 2 x 10^{29} years is obtained at 90%
confidence for either neutron or proton decay modes. This is about an order of
magnitude more stringent than previous constraints on invisible proton decay
modes and 400 times more stringent than similar neutron modes.Comment: Update includes missing efficiency factor (limits change by factor of
2) Submitted to Physical Review Letter
First Neutrino Observations from the Sudbury Neutrino Observatory
The first neutrino observations from the Sudbury Neutrino Observatory are
presented from preliminary analyses. Based on energy, direction and location,
the data in the region of interest appear to be dominated by 8B solar
neutrinos, detected by the charged current reaction on deuterium and elastic
scattering from electrons, with very little background. Measurements of
radioactive backgrounds indicate that the measurement of all active neutrino
types via the neutral current reaction on deuterium will be possible with small
systematic uncertainties. Quantitative results for the fluxes observed with
these reactions will be provided when further calibrations have been completed.Comment: Latex, 7 pages, 10 figures, Invited paper at Neutrino 2000
Conference, Sudbury, Canada, June 16-21, 2000 to be published in the
Proceeding
Utilisation of an operative difficulty grading scale for laparoscopic cholecystectomy
Background
A reliable system for grading operative difficulty of laparoscopic cholecystectomy would standardise description of findings and reporting of outcomes. The aim of this study was to validate a difficulty grading system (Nassar scale), testing its applicability and consistency in two large prospective datasets.
Methods
Patient and disease-related variables and 30-day outcomes were identified in two prospective cholecystectomy databases: the multi-centre prospective cohort of 8820 patients from the recent CholeS Study and the single-surgeon series containing 4089 patients. Operative data and patient outcomes were correlated with Nassar operative difficultly scale, using Kendall’s tau for dichotomous variables, or Jonckheere–Terpstra tests for continuous variables. A ROC curve analysis was performed, to quantify the predictive accuracy of the scale for each outcome, with continuous outcomes dichotomised, prior to analysis.
Results
A higher operative difficulty grade was consistently associated with worse outcomes for the patients in both the reference and CholeS cohorts. The median length of stay increased from 0 to 4 days, and the 30-day complication rate from 7.6 to 24.4% as the difficulty grade increased from 1 to 4/5 (both p < 0.001). In the CholeS cohort, a higher difficulty grade was found to be most strongly associated with conversion to open and 30-day mortality (AUROC = 0.903, 0.822, respectively). On multivariable analysis, the Nassar operative difficultly scale was found to be a significant independent predictor of operative duration, conversion to open surgery, 30-day complications and 30-day reintervention (all p < 0.001).
Conclusion
We have shown that an operative difficulty scale can standardise the description of operative findings by multiple grades of surgeons to facilitate audit, training assessment and research. It provides a tool for reporting operative findings, disease severity and technical difficulty and can be utilised in future research to reliably compare outcomes according to case mix and intra-operative difficulty
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Measurement of neutron production in atmospheric neutrino interactions at the Sudbury Neutrino Observatory
Neutron production in GeV-scale neutrino interactions is a poorly studied
process. We have measured the neutron multiplicities in atmospheric neutrino
interactions in the Sudbury Neutrino Observatory experiment and compared them
to the prediction of a Monte Carlo simulation using GENIE and a minimally
modified version of GEANT4. We analyzed 837 days of exposure corresponding to
Phase I, using pure heavy water, and Phase II, using a mixture of Cl in heavy
water. Neutrons produced in atmospheric neutrino interactions were identified
with an efficiency of and , for Phase I and II respectively.
The neutron production is measured as a function of the visible energy of the
neutrino interaction and, for charged current quasi-elastic interaction
candidates, also as a function of the neutrino energy. This study is also
performed classifying the complete sample into two pairs of event categories:
charged current quasi-elastic and non charged current quasi-elastic, and
and . Results show good overall agreement between data and
Monte Carlo for both phases, with some small tension with a statistical
significance below for some intermediate energies
Search for invisible modes of nucleon decay in water with the SNO+ detector
This paper reports results from a search for nucleon decay through invisible modes, where no visible energy is directly deposited during the decay itself, during the initial water phase of SNO+. However, such decays within the oxygen nucleus would produce an excited daughter that would subsequently deexcite, often emitting detectable gamma rays. A search for such gamma rays yields limits of 2.5×1029 y at 90% Bayesian credibility level (with a prior uniform in rate) for the partial lifetime of the neutron, and 3.6×1029 y for the partial lifetime of the proton, the latter a 70% improvement on the previous limit from SNO. We also present partial lifetime limits for invisible dinucleon modes of 1.3×1028 y for nn, 2.6×1028 y for pn and 4.7×1028 y for pp, an improvement over existing limits by close to 3 orders of magnitude for the latter two
Population‐based cohort study of outcomes following cholecystectomy for benign gallbladder diseases
Background The aim was to describe the management of benign gallbladder disease and identify characteristics associated with all‐cause 30‐day readmissions and complications in a prospective population‐based cohort. Methods Data were collected on consecutive patients undergoing cholecystectomy in acute UK and Irish hospitals between 1 March and 1 May 2014. Potential explanatory variables influencing all‐cause 30‐day readmissions and complications were analysed by means of multilevel, multivariable logistic regression modelling using a two‐level hierarchical structure with patients (level 1) nested within hospitals (level 2). Results Data were collected on 8909 patients undergoing cholecystectomy from 167 hospitals. Some 1451 cholecystectomies (16·3 per cent) were performed as an emergency, 4165 (46·8 per cent) as elective operations, and 3293 patients (37·0 per cent) had had at least one previous emergency admission, but had surgery on a delayed basis. The readmission and complication rates at 30 days were 7·1 per cent (633 of 8909) and 10·8 per cent (962 of 8909) respectively. Both readmissions and complications were independently associated with increasing ASA fitness grade, duration of surgery, and increasing numbers of emergency admissions with gallbladder disease before cholecystectomy. No identifiable hospital characteristics were linked to readmissions and complications. Conclusion Readmissions and complications following cholecystectomy are common and associated with patient and disease characteristics
Tests of Lorentz invariance at the Sudbury Neutrino Observatory
Experimental tests of Lorentz symmetry in systems of all types are critical
for ensuring that the basic assumptions of physics are well-founded. Data from
all phases of the Sudbury Neutrino Observatory, a kiloton-scale heavy water
Cherenkov detector, are analyzed for possible violations of Lorentz symmetry in
the neutrino sector. Such violations would appear as one of eight possible
signal types in the detector: six seasonal variations in the solar electron
neutrino survival probability differing in energy and time dependence, and two
shape changes to the oscillated solar neutrino energy spectrum. No evidence for
such signals is observed, and limits on the size of such effects are
established in the framework of the Standard Model Extension, including 40
limits on perviously unconstrained operators and improved limits on 15
additional operators. This makes limits on all minimal, Dirac-type Lorentz
violating operators in the neutrino sector available for the first time
Search for hep solar neutrinos and the diffuse supernova neutrino background using all three phases of the Sudbury Neutrino Observatory
A search has been performed for neutrinos from two sources, the hep reaction in the solar pp fusion chain and the νe component of the diffuse supernova neutrino background (DSNB), using the full dataset of the Sudbury Neutrino Observatory with a total exposure of 2.47 kton-years after fiducialization. The hep search is performed using both a single-bin counting analysis and a likelihood fit. We find a best-fit flux that is compatible with solar model predictions while remaining consistent with zero flux, and set a one-sided upper limit of φhep<30×103 cm-2 s-1 [90% credible interval (CI)]. No events are observed in the DSNB search region, and we set an improved upper bound on the νe component of the DSNB flux of φνeDSNB<19 cm-2 s-1 (90% CI) in the energy range 22.9<Eν<36.9 MeV
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