45 research outputs found
The singular St. Peter and St. Paul Archipelago, equatorial Atlantic, Brazil
No full textThe St. Peter and St. Paul archipelago (SPSPA) is composed of abyssal mantle rocks. It consists of a small group of islets (five) and rocks (five), located near the axis of the Mid-Atlantic Ridge, in an inside corner position on the southern edge of the northern transform limit of the St. Paul Transform Fault System. The archipelago forms the summit of the Atoba Ridge, lying about 100km north of the Equator at 0 degrees 55′N and 29 degrees 20′43′′W The Atoba Ridge is a pressure ridge of the St. Paul Transform Fault System that was uplifted by local compression along the boundary between the African and South American Plates. The almost NNW–SSE compressional stress has been active for the last 6600years before present, providing an uplift rate of approximately 1.5mm/year, as suggested by teleseismic evidence. The SPSPA is thus seismically active; predictably, most of its earthquakes show predominantly east–west right-lateral strike-slip displacement along the St. Paul Fracture (33 focal mechanisms of earthquakes Mb≥5.4), coherent with the offset sense of the transform fault. However, in the south of the SPSPA, there were a significant number of compressive earthquakes (four focal mechanisms of earthquakes Mb≥5.8) that show a secondary stress component of NNW–SSE compression, revealing differential movement and independent behavior between the islets. Thus, the SPSPA is an upper mantle block that was uplifted tectonically during strike-slip movement as part of an extensively sheared and thrust-faulted transverse ridge. During ascent and emplacement at high mantle temperatures in a transitional plastic-brittle regime, intense mylonitization took place, producing progressive grain size reduction. Anhydrous fluids could not penetrate the rock during the plastic regime, but only after their uplift, it transferred them into a brittle regime; therefore, the peridotite mylonites were serpentinized from the joints. The rocks chemically correspond to harzburgite, and more rarely dunite, along with rare kaersutite-rich alkaline ultramafic dikes. The latter rock type is millimetrically interlayered with peridotite rock. These rocks are ultramylonitized and pervasively reduced to a very fine grain size. Mass-balance calculations of whole-rock geochemical data indicate that the early mylonitization did not significantly change the major peridotite composition. The emerged spinel- and pargasite-peridotites of St. Peter and St. Paul are residual mantle rocks after 3%–13% of partial melting, and the major, trace rare earth element patterns of whole-rock and nonzoned minerals suggest that these residual peridotites of SPSPA resulted from mixing of peridotite and kaersutite mafic end-members. The alkaline fluids derived from low melting mantle (about 1.0%) that percolated, reacted with, and refertilized the residual mantle of the SPSPA by chromatographic effects. The kaersutite layers of the layered peridotite-kaersutite ultramylonite probably formed by freezing of the trapped fluids that percolated the peridotite before the mylonitization of fluid conduits
Determination of Liquid Scintillator Purity for the Jiangmen Underground Neutrino Observatory
No full textThe Jiangmen Underground Neutrino Observatory (JUNO) is a neutrino experiment currently under construction in southern China. Its primary goal is the determination of the neutrino mass ordering by a spectral analysis of the reactor neutrino flux from two nearby nuclear power plants at a distance of 53 km using a 20 kt liquid scintillator (LS) detector.
As the neutrinos are identified indirectly through measurement of scintillation light within the LS, it is imperative for the liquid to be as clean as possible and its properties sufficiently known. This thesis deals with both, optical and radioactive characteristics, and describes methods of determining scattering parameters and radioactive contamination of the LS.
The first part of the thesis investigates Rayleigh scattering in the LS by means of a laboratory setup that illuminates samples with polarized light of selectable wavelengths while two photomultiplier tubes (PMTs) measure both, the throughgoing intensity and the emissions at 90◦ perpendicular to the beam path. Comparing the two allows to identify the so-called Rayleigh length of the respective sample. Rayleigh scattering is the dominant process determining the transparency of the LS to the scintillation light. The setup was calibrated using various samples with known scattering behaviour before conducting LS investigations. The resulting Rayleigh lengths of (26.1 ± 1.2stat ± 2.6sys) m for a pure LAB sample and (22.4 ± 0.7_stat ± 2.2_sys) m for a sample of SHiP scintillator at 430 nm are in agreement with expectations around 28 m and show the anticipated λ^4-dependence in the region above, but deviate for lower wavelengths. This discrepancy was verified with a spectrometer and suggests either contamination of the samples in question, divergent behaviour in proximity of the LS absorption/emission region or both and thus needs to be studied further.
In the second part of the thesis, a radioactivity pre-detector for JUNO is envisioned and developed. The Online Scintillator Internal Radioactivity Investigation System (OSIRIS) will determine the radioactive contamination of the LS by a rate analysis of 214Bi-214Po-coincidence-signals compared to the accepted background rate. A Monte Carlo simulation was created in Geant4 to study the feasibility of such a device and investigate various designs with regards to their efficiency. Several concept stages are briefly shown and the final simulation is described, along with data production, processing and analysis methods. The simulation data shows that a nested arrangement of cylindrical tanks with a 3 m LS volume, a ∼ 5 m buffer housing 100 8" PMTs and an 8 m water shield is able to determine radioactive contaminations up to 2.22 · 10^−10 Bq/kg within 24 hours using a 50 cm fiducial volume cut. This is sufficient to verify the baseline purity requirements for solar neutrino investigation in JUNO (1.24 · 10^−9 Bq/kg) as well as the requirements for the mass ordering search (1.24 · 10^−8 Bq/kg).V, 130 Blätter, Illustrationen, Diagramm
Denudation history of the Great Escarpment in the southwestern flank of the Angola (Bié) Dome, Africa
No full textThe origin of the topography and relief of southern Africa has been the subject of intense debate. The landscape is characterized by a high, low-relief inland plateau, separated from the low-lying coastal region by a remarkably steep escarpment, known as the “Great Escarpment”. In this paper, we bring new insights into the denudation history of the southwestern Angolan margin by providing new apatite (U-Th-Sm)/He data from the Chela Escarpment, one of the steepest stretches of the African Great Escarpment. In addition, we performed morphometric analysis of the river network to access the interplay between rock uplift and erosion of both the interior and coastal river catchments. The new apatite (U-Th-Sm)/He data combined with previous published thermochronological data show that seaward of the Chela Escarpment summit, the last denudation event commenced at ~ 40–20 Ma, whereas the top of the scarp appears to have undergone the last denudation event at ~ 120–70 Ma with relatively low Cenozoic denudation. The new morphometric data suggest that fluvial incision rates are typically higher for the coastal rivers in comparison to those farther inland, and that as the coastal rivers erode backwards they tend to dissect the plateau surface, causing river captures, and the migration of the drainage divide farther inland. As this margin segment lies at the southwestern side of the Angola Dome, we propose that the Chela Escarpment has been formed primarily by the dissection of the dome flank, since the Late Cenozoic, in a manner comparable to that which (Burke and Gunnell, The african erosion surface: a continental-scale synthesis of geomorphology, tectonics, and environmental change over the past 180 million years, memoir 201, Geological Society of America, Boulder, Colorado, 2008) propose for the Great Escarpment formation in southern Africa. In this scenario, the river network responding to the crustal uplifts and steepening of the land surface, base-level falls, and relatively humid climatic conditions, appears to account for this model of landscape evolution.Departamento de Geologia Universidade Estadual Paulista Instituto de Geociências e Meio Ambiente, São PauloUniversidade de São Paulo Instituto de Energia e Ambiente, São PauloSecretaria de Infraestrutura e Meio Ambiente Instituto Geológico, São PauloInstitute of Earth Sciences Heildelberg UniversityDepartamento de Geologia Universidade Estadual Paulista Instituto de Geociências e Meio Ambiente, São Paul
JUNO Sensitivity on Proton Decay Searches
No full textThe Jiangmen Underground Neutrino Observatory (JUNO) is a large liquid
scintillator detector designed to explore many topics in fundamental physics.
In this paper, the potential on searching for proton decay in mode with JUNO is investigated.The kaon and its decay particles feature a
clear three-fold coincidence signature that results in a high efficiency for
identification. Moreover, the excellent energy resolution of JUNO permits to
suppress the sizable background caused by other delayed signals. Based on these
advantages, the detection efficiency for the proton decay via is 36.9% with a background level of 0.2 events after 10 years of data
taking. The estimated sensitivity based on 200 kton-years exposure is years, competitive with the current best limits on the proton
lifetime in this channel.Comment: 14 pages, 12 figures, an author adde
Titanian Ixiolite-niobian Rutile Intergrowths From The Borborema Pegmatitic Province, Northeastern Brazil
No full textIntergrowths of orthorhombic and tetragonal Nb-Ta-Ti-(Sn) oxides were at first recognized by conventional X-ray diffraction and electron-microprobe analyses in six pegmatite occurrences of the Borborema. Pegmatitic Province in northeastern Brazil. In three of these cases, electron-diffraction patterns (HRTEM) on chips 0.15 μm thick obtained by focused ion-beam (FIB) sampling were necessary to confirm the preliminary identification of titanian ixiolite. Electron-microprobe analyses reveal very variable bulk-compositions and extents of compositional gaps between the coexisting tetragonal and orthorhombic phases in the Nb,Ta - Ti,Sn - Fe,Mn triangular plot. This behavior is difficult to explain as a result of a simple solvus along a pseudobinary section between rutile and tapiolite - columbite - ixiolite - wodginite. In two of six cases, the data obtained plot exactly within the compositional gaps observed between these phases in other pegmatitic provinces. This apparent violation of the gap is due to abnormally high Ti-contents in ixiolite and high levels of Th + Nb (up to 55 wt.% Nb + Ta oxides) observed in the tetragonal phase. Therefore, in the cases studied, the observed trends and gaps seem to be the result of disequilibrium (or incomplete equilibrium) between the coexisting phases, despite the exsolution-like, cuneiform to vermicular intergrowths observed in three of the occurrences studied. Compositional growth-zoning observed in the other cases agrees with the hypothesis of disequilibrium. In five of the six cases, a partition of Ta and Fe in favor of the tetragonal phase and of Nb and Mn in the coexisting orthorhombic phase is observed; it agrees with the behavior of similar intergrowths elsewhere. The sixth case is noteworthy because of the higher Ta:Nb ratio in the ixiolite in comparison with the coexisting niobian rutile. This enrichment of Nb and Fe from core to rim represents an anomalous pattern of fractionation behavior.45613671387ADUSUMILI, M.P.S. (1978): Nióbio-tantalatos do Nordeste do Brasil: a série columbita-tantalita. Jornal de Mineralogia 7, 195-225ALMEIDA, F.F.M., MELCHER, G.C., CORDANI, U.G., KAWASHITA, K., VANDOROS, P., Radiometric age determinations from northern Brazil. São Paulo (1968) Soc. Bras. Geol. Bol, 17, pp. 3-15ARAÚJO, M.N.C., SILVA, F.C.A., JARDIM, DE SÁ, E.F., Pegmatite emplacement in the Seridó Belt, northeastern Brazil: Late stage tectonics of the Brasiliano Orogen (2001) Gondwana Res, 4, pp. 75-85ARAUJO, M.N.C., VASCONCELOS, P.M., SILVA, F.C.A., JARDIM, DE SÁ, E.F., SÁ, J.M., 40Ar/39Ar geochronology of gold mineralization in Brasiliano strike-slip shear zones in the Borborema province, NE Brazil (2005) J. S. Am. Earth Sci, 19, pp. 445-460BAUMGARTNER, R., MORITZ, R., ROMER, R. & SALLET, R. 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Potential for a precision measurement of solar neutrinos in the Serappis Experiment
No full textThe Serappis (SEarch for RAre PP-neutrinos In Scintillator) project aims at a precision measurement of the flux of solar neutrinos on the few-percent level. Such a measurement will be a relevant contribution to the study of solar neutrino oscillation parameters and a sensitive test of the solar luminosity constraint. The concept of Serappis relies on a small organic liquid scintillator detector (20 m) with excellent energy resolution (2.5 % at 1 MeV), low internal background and sufficient shielding from surrounding radioactivity. This can be achieved by a minor upgrade of the OSIRIS facility at the site of the JUNO neutrino experiment in southern China. To go substantially beyond current accuracy levels for the flux, an organic scintillator with ultra-low C levels (below ) is required. The existing OSIRIS detector and JUNO infrastructure will be instrumental in identifying suitable scintillator materials, offering a unique chance for a low-budget high-precision measurement of a fundamental property of our Sun that will be otherwise hard to access
Prospects for Detecting the Diffuse Supernova Neutrino Background with JUNO
No full textWe present the detection potential for the diffuse supernova neutrino background (DSNB) at the Jiangmen Underground Neutrino Observatory (JUNO), using the inverse-beta-decay (IBD) detection channel on free protons. We employ the latest information on the DSNB flux predictions, and investigate in detail the background and its reduction for the DSNB search at JUNO. The atmospheric neutrino induced neutral current (NC) background turns out to be the most critical background, whose uncertainty is carefully evaluated from both the spread of model predictions and an envisaged \textit{in situ} measurement. We also make a careful study on the background suppression with the pulse shape discrimination (PSD) and triple coincidence (TC) cuts. With latest DSNB signal predictions, more realistic background evaluation and PSD efficiency optimization, and additional TC cut, JUNO can reach the significance of 3 for 3 years of data taking, and achieve better than 5 after 10 years for a reference DSNB model. In the pessimistic scenario of non-observation, JUNO would strongly improve the limits and exclude a significant region of the model parameter space
Detection of the Diffuse Supernova Neutrino Background with JUNO
No full textAs an underground multi-purpose neutrino detector with 20 kton liquid scintillator, Jiangmen Underground Neutrino Observatory (JUNO) is competitive with and complementary to the water-Cherenkov detectors on the search for the diffuse supernova neutrino background (DSNB). Typical supernova models predict 2-4 events per year within the optimal observation window in the JUNO detector. The dominant background is from the neutral-current (NC) interaction of atmospheric neutrinos with 12C nuclei, which surpasses the DSNB by more than one order of magnitude. We evaluated the systematic uncertainty of NC background from the spread of a variety of data-driven models and further developed a method to determine NC background within 15\% with {\it{in}} {\it{situ}} measurements after ten years of running. Besides, the NC-like backgrounds can be effectively suppressed by the intrinsic pulse-shape discrimination (PSD) capabilities of liquid scintillators. In this talk, I will present in detail the improvements on NC background uncertainty evaluation, PSD discriminator development, and finally, the potential of DSNB sensitivity in JUNO
Feasibility of detecting B8 solar neutrinos at JUNO
No full textThe Jiangmen Underground Neutrino Observatory (JUNO) features a 20 kt multi-purpose underground
liquid scintillator sphere as its main detector. In this talk we describe in detail a comprehensive assessment of JUNO's potential for detecting 8B solar neutrinos via the neutrino-electron elastic scattering process. A reduced 2 MeV threshold for the recoil electron energy is achievable with optimized background reduction strategies. With ten years of data taking, about 60,000 signal and 30,000 background events are expected. This leads to a simultaneous measurement of sin2θ12 and Δm221 using reactor antineutrinos and solar neutrinos in the JUNO detector. This large sample will enable an examination of the distortion of the recoil electron spectrum that is dominated by the neutrino flavor transformation in the dense solar matter. If Δm221=4.8×10−5(7.5×10−5eV2), JUNO can provide evidence of neutrino oscillation in the Earth at approximately the 3σ (2σ) level by measuring the non-zero signal rate variation with respect to the solar zenith angle. Moreover, JUNO can simultaneously measure Δm221 using 8B solar neutrinos to a precision of 20% or better, depending on the central value, and to sub-percent precision using reactor antineutrinos. A comparison of these two measurements from the same detector will help understand the current mild inconsistency between the value of reported by solar neutrino experiments and the KamLAND experiment
