69 research outputs found

    ArgonCube – A Novel Concept for Liquid Argon Time Projection Chambers

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    Neutrinos are elementary particles that allow for the study of some of the most fundamental questions in particle physics, e.g. the matter-antimatter asymmetry observed in the Universe. Current and future neutrino experiments are designed to measure the properties of these particles with unprecedented accuracy to answer those questions. For this purpose, large data samples collected with very sensitive and precise detectors are required. The Liquid Argon Time Projection Chamber (LArTPC) is an ideal detector for neutrino experiments as it provides accurate particle tracking and calorimetric information, and it can be scaled to large active masses for the collection of high-statistics data samples. However, monolithic LArTPCs face the problem of large cathode bias voltages of several 100 kV and a large amount of stored energy in the drift field, posing the risk of severe damage in the case of electric breakdowns. Furthermore, traditional LArTPCs employ projective wire readout systems, which introduce ambiguities in the 3-dimensional (3D) event reconstruction. The event reconstruction using data acquired with a projective wire readout is particularly challenging in high-multiplicity environments where several particle interactions can overlap within the drift window of the LArTPC. To address these problems, the ArgonCube collaboration developed a novel LArTPC design that segments the total detector volume into several electrically and optically isolated LArTPCs sharing a common cryostat. In this way, the cathode bias voltages and the stored energies within the detector’s drift fields are reduced. Furthermore, the inactive volume of the ArgonCube detector is reduced using new technology to shape the electric field. This technology would slow down the energy released in the case of an electric breakdown. The ArgonCube design furthermore employs a pixelated charge readout system that provides unambiguous particle tracking in 3D. In addition, a dielectric light detection system, sensitive to the Liquid Argon (LAr) scintillation light and with an excellent time resolution of O(1 ns), was developed. These detectors enable a precise association of detached energy depositions to specific neutrino interaction vertices, enabling an improved accuracy of the LArTPC event reconstruction. This thesis motivates the use of LArTPCs in neutrino experiments and describes the novel ArgonCube concepts and technologies. Furthermore, the design and results of several prototypes used to study the performance of the ArgonCube technologies are presented. For the detector calibration, neutral pions decaying within a LArTPC can be used as standard candles. A method based on machine-learning techniques to reconstruct neutral pion decays in a modular LArTPC environment is presented. ArgonCube found application in the Near-Detector (ND) of the Deep Underground Neutrino Experiment (DUNE) and has been proposed for one of the Far-Detector (FD) units of the experiment

    First Operation of a Resistive Shell Liquid Argon Time Projection Chamber -- A new Approach to Electric-Field Shaping

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    We present a new technology for the shaping of the electric field in Time Projection Chambers (TPCs) using a carbon-loaded polyimide foil. This technology allows for the minimisation of passive material near the active volume of the TPC and thus is capable to reduce background events originating from radioactive decays or scattering on the material itself. Furthermore, the high and continuous electric resistivity of the foil limits the power dissipation per unit area and minimizes the risks of damages in the case of an electric field breakdown. Replacing the conventional field cage with a resistive plastic film structure called 'shell' decreases the number of components within the TPC and therefore reduces the potential points of failure when operating the detector. A prototype liquid argon (LAr) TPC with such a resistive shell and with a cathode made of the same material was successfully tested for long term operation with electric field values up to about 1.5 kV/cm. The experiment shows that it is feasible to successfully produce and shape the electric field in liquefied noble-gas detectors with this new technology.Comment: 13 page

    A New Concept for Kilotonne Scale Liquid Argon Time Projection Chambers

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    We develop a novel Time Projection Chamber (TPC) concept suitable for deployment in kilotonne-scale detectors, with a charge-readout system free from reconstruction ambiguities, and a robust TPC design that reduces high-voltage risks while increasing the coverage of the light-collection system and maximizing the active volume. This novel concept could be used as a far detector module in the Deep Underground Neutrino Experiment (DUNE). For the charge-readout system, we used the charge-collection pixels and associated application-specific integrated circuits currently being developed for the liquid argon (LAr) component of the DUNE Near Detector design, ArgonCube. In addition, we divided the TPC into a number of shorter drift volumes, reducing the total voltage used to drift the ionization electrons, and minimizing the stored energy per TPC. Segmenting the TPC also contains scintillation light, allowing for precise trigger localization and a more expansive light-readout system. Furthermore, the design opens the possibility of replacing or upgrading components. These augmentations could substantially improve the reliability and the sensitivity, particularly for low-energy signals, in comparison to traditional monolithic LArTPCs with projective-wire charge readouts

    A model for uranium, rhenium, and molybdenum diagenesis in marine sediments based on results from coastal locations

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    Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 73 (2009): 2938-2960, doi:10.1016/j.gca.2009.02.029.The purpose of this research is to characterize the mobilization and immobilization processes that control the authigenic accumulation of uranium (U), rhenium (Re) and molybdenum (Mo) in marine sediments. We analyzed these redox– sensitive metals (RSM) in benthic chamber, pore water and solid phase samples at a site in Buzzards Bay, Massachusetts, U.S.A., which has high bottom water oxygen concentrations (230–300 mol/L) and high organic matter oxidation rates (390 mol C/cm2/y). The oxygen penetration depth varies from 2–9 mm below the sediment–water interface, but pore water sulfide is below detection (< 2M). The RSM pore water profiles are modeled with a steady–state diagenetic model that includes irrigation, which extends 10–20 cm below the sediment–water interface. To present a consistent description of trace metal diagenesis in marine sediments, RSM results from sediments in Buzzards Bay are compared with previous research from sulfidic sediments (Morford et al., GCA 71). Release of RSM to pore waters during the remineralization of solid phases occurs near the sediment–water interface at depths above the zone of authigenic RSM formation. This release occurs consistently for Mo at both sites, but only in the winter for Re in Buzzards Bay and intermittently for U. At the Buzzards Bay site, Re removal to the solid phase extends to the bottom of the profile, while the zone of removal is restricted to ~2–9 cm for U and Mo. Authigenic Re formation is independent of the anoxic remineralization rate, which is consistent with an abiotic removal mechanism. The rate of authigenic U formation and its modeled removal rate constant increase with increasing anoxic remineralization rates, and is consistent with U reduction being microbially mediated. Authigenic Mo formation is related to the formation of sulfidic microenvironments. The depth and extent of Mo removal from pore water is closely associated with the balance between iron and sulfate reduction and the consumption of pore water sulfide via iron sulfide formation. Pore water RSM reach constant asymptotic concentrations in sulfidic sediments, but only pore water Re is constant at depth in Buzzards Bay. The increases in pore water U at the Buzzards Bay site are consistent with addition via irrigation and subsequent upward diffusion to the removal zone. Deep pore water Mo concentrations exceed its bottom water concentration due to irrigation–induced oxidation and remobilization from the solid phase. In sulfidic sediments, there is no evidence for higher pore water U or Mo concentrations at depth due to the absence of irrigation and/or the presence of more stable authigenic RSM phases. There are good correlations between benthic fluxes and authigenic accumulation rates for U and Mo in sulfidic sediments. However, results from Buzzards Bay suggest irrigation ultimately results in the partial loss of U and Mo from the solid phase, with accumulation rates that are 20–30% of the modeled flux. Irrigation can augment (Re, possibly U) or compromise (U, Mo) authigenic accumulation in sediments, and is important when determining burial rates in continental margin sediments.The authors also acknowledge financial support from the National Science Foundation (JLM, WRM: OCE–0220892), Research Corporation (JLM, CMC), Franklin & Marshall College, and the Hackman Summer Research Program at F&M

    Automated airport staff scheduling at Swissport International Ltd.

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    Spatial heterogeneity of arsenic in a deltaic groundwater environment of West Bengal, India

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    The water quality and chemistry of the groundwater samples collected from rural West Bengal have been investigated. The investigation focuses on the multiple As mobilization processes taking place simultaneously. The groundwater arsenic (As) distribution and their relationships with land-use pattern suggest the influence of local conditions (e.g. sanitation, presence of surface water bodies, agricultural practice). The As release mechanism is complex with observation of patchy (spatio-vertical heterogeneity) As hot spots. Unique/individual mechanism is difficult to link with the heterogeneous distribution of As. Local conditions may contribute to some extent to explain the heterogeneity in arsenic distribution and mobilization pattern along with geology and hydrogeology. © 2012 Taylor & Francis Group
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