The instrumentation for a pathfinder mission towards a possible large scale neutrino telescope named "STRings for Absorption length in Water" (STRAW) is presented in terms of design and performance. In June 2018 STRAW was deployed at the Cascadia Basin site operated by Ocean Networks Canada and has been collecting data since then. At a depth of about 2600 meters, the two STRAW 120 meters tall mooring lines are instrumented by three "Precision Optical Calibration Modules" (POCAM) and five Digital Optical Sensors (sDOM). The main objectives of STRAW are the measurement of light extinction in different wavelength bands and bioluminescence at Cascadia Basin. We describe the instrumentation deployed in the Pacific Ocean and show some data from the first measurements.
Purpose:Development of a photon detection system designed for online range verification of laser‐accelerated proton beams via prompt‐gamma imaging of nuclear reactions.Methods:We develop a Compton camera for the position‐sensitive detection of prompt photons emitted from nuclear reactions between the proton beam and biological samples. The detector is designed to be capable to reconstruct the photon source origin not only from the Compton scattering kinematics of the primary photon, but also to allow for tracking of the Compton‐scattered electrons.Results:Simulation studies resulted in the design of the Compton camera based on a LaBr3(Ce) scintillation crystal acting as absorber, preceded by a stacked array of 6 double‐sided silicon strip detectors as scatterers. From the design simulations, an angular resolution of ≤ 2° and an image reconstruction efficiency of 10−3 −10−5 (at 2–6 MeV) can be expected. The LaBr3 crystal has been characterized with calibration sources, resulting in a time resolution of 273 ps (FWHM) and an energy resolution of about 3.8% (FWHM). Using a collimated (1 mm diameter) 137Cs calibration source, the light distribution was measured for each of 64 pixels (6×6 mm2). Data were also taken with 0.5 mm collimation and 0.5 mm step size to generate a reference library of light distributions that allows for reconstructing the interaction position of the initial photon using a k‐nearest neighbor (k‐NN) algorithm developed by the Delft group.Conclusion:The Compton‐camera approach for prompt‐gamma detection offers promising perspectives for ion beam range verification. A Compton camera prototype is presently being developed and characterized in Garching. Furthermore, an arrangement of, e.g., 4 camera modules could even be used in a ‘gamma‐PET’ mode to detect delayed annihilation radiation from positron emitters in the irradiation interrupts (with improved performance in the presence of an additional third (prompt) photon (as in 10C and 14O).This work was supported by the DFG Cluster of Excellence MAP (Munich‐Centre for Advanced Photonics)
STRAW-STRings for Absorption Length in Water is a project aimed at investigating the optical properties (scattering and absorption length, in particular) of the deep-sea water at Cascadia Basin (British Columbia, Canada). This is the first step of a broader feasibility study for a future large-scale neutrino telescope in the Pacific Ocean. Two strings equipped with 5 modules for light detection (sDOM-Straw Digital Optical Module) and 3 modules for light emission (POCAM-Precision Optical CAlibration Module) have been deployed in June 2018 and connected to the deep-sea infrastructure of Ocean Networks Canada (ONC). The work has covered the process of designing, building and calibrating of the sDOM and the POCAM (already deployed with success in GVD-Baikal in March 2017). An accurate description of the system follows, with special focus on the used technologies and on preliminary results of data-taking.
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