The CLARO8 chip has been designed for single-photon counting in the upgraded RICH detector of the LHCb experiment at CERN. The chip has 8 channels with 5ns peaking time and a recovery time better ...than 25ns. Each channel is made of a charge amplifier with 2-bit settable attenuation, plus a comparator with a 6-bit settable threshold, and the configuration register is protected against Single Event Upsets by triple modular redundancy. In order to ensure stable operation of the upgraded RICH detectors over the expected lifetime of the experiment after the upgrade, the performance of the CLARO8 in high radiation fields has been assessed. These chips will be exposed, during the whole upgrade running phase, to a total ionizing dose of 200krad, a neutron fluence of 3×1012 1MeVneq/cm2 and a high energy hadrons fluence of 1.2×1012cm−2. Systematic irradiation campaigns have been performed using ions, protons and mixed-field high-energy hadron beams. This paper describes the radiation hardness campaign of the CLARO8 chips and the main results of its extensive characterisation.
Signal-induced noise is observed in Hamamatsu R11265 Multianode Photomultiplier Tubes, manifesting up to several microseconds after the single photoelectron response signal and localised in specific ...anodes. The mean number of noise pulses varies between devices, and shows significant dependence on the applied high-voltage. The characterisation of this noise and the mitigation strategies to perform optimal single-photon counting at 40 MHz, as required by the LHCb Ring-Imaging Cherenkov detectors, are reported.
The performance of the ring-imaging Cherenkov detectors at the LHCb experiment is determined during the LHC Run 2 period between 2015 and 2018. The stability of the Cherenkov angle resolution and ...number of detected photons with time and running conditions is measured. The particle identification performance is evaluated with data and found to satisfy the requirements of the physics programme.
Ferrero Bay, located in eastern Pine Island Bay (PIB) of the Amundsen Sea Embayment, is one of the largest and southernmost fjords yet studied in Antarctica. High-resolution multibeam swath ...bathymetric data, chirp sonar sub-bottom profiles, and three Kasten cores were collected in Ferrero Bay during the IB Oden Southern Ocean 2009–2010 cruise (OSO0910). Core KC-15 from the inner bay yielded two carbonate ages providing a minimum age for ice sheet recession from this sector of PIB by ~11 cal. kyr BP. In total, seven additional acid insoluble organic (AIO) fraction radiocarbon ages provide a linear age model with an R2 of 0.99. Variations in magnetic susceptibility, grain size, total organic carbon (TOC) and nitrogen, diatom abundance, and foraminiferal assemblage and abundance are used to interpret glacial history and paleoceanographic conditions. Grounding line retreat was characterized by advection of planktic foraminifera beneath an ice shelf that may have extended across the middle continental shelf. Following initial deglaciation, the Cosgrove Ice Shelf covered Ferrero Bay, and productivity was virtually absent during the mid-Holocene, while benthic foraminifera indicate periodic incursion of warm Circumpolar Deep Water. The ice shelf persisted until 2.3 cal. kyr BP, when TOC and diatom abundance increased as the bay opened and coastal areas deglaciated. Abundant diatoms demonstrate open marine conditions and seasonal sea ice during the recent open water phase, while high benthic foraminiferal abundance indicates active benthos. The retreat of the Cosgrove Ice Shelf was out of phase with Antarctic Peninsula ice shelves and ice-core proxy temperatures, implying that it did not respond to Holocene climate events but rather to the influence of Circumpolar Deep Water and possibly to internal glacial dynamics.
The sediment record offshore James Ross Island, northeast Antarctic Peninsula presents an unparalleled opportunity to directly compare marine and terrestrial climate records spanning the Holocene in ...maritime Antarctica. An 11 m drill core was collected between Herbert Sound and Croft Bay as part of the SHALDRIL NBP-0502 initiative and produced the southernmost sediment record from the eastern side of the AP. Thirty-eight radiocarbon ages are used to construct an age model of centennial-scale resolution. Multi-proxy records, including magnetic susceptibility, pebble content, particle size, total organic carbon, and diatom assemblages, were interrogated in the context of nearby Holocene-age ice core, lake, and drift records from James Ross Island. Differences in the timing and expression of Holocene events reflect marine controls on tidewater glaciers, such as water mass configurations and sea ice. Glacial behavior mimics ice core paleotemperatures during the Holocene, with the exception of distinct ocean warming events. Herbert Sound was fully occupied by grounded ice during the Last Glacial Maximum, and experienced rapid lift-off, followed by a floating ice phase. The canopy of floating ice receded by 10 ± 2.4 cal kyr BP, presumably in response to Early Holocene warming. Herbert Sound and Croft Bay fully deglaciated by 7.2 cal kyr BP, when the Mid Holocene Hypsithermal commenced and the sound became open and productive. An extreme peak in productivity ∼6.1 cal kyr BP indicates an oceanic warming event that is not reflected in atmospheric temperature or lacustrine sediment records. Increase in sea ice cover and ice rafting mark the onset of the Neoglacial ∼2.5 cal kyr BP, when pronounced atmospheric cooling is documented in the James Ross Island ice core. Our comparison facilitates more holistic understanding of atmosphere-ocean-cryosphere interactions that may aid predictions of glacial response to future warming and sea-level scenarios.
•We present the Holocene glacimarine record from Herbert Sound, James Ross Island.•Marine record is compared to nearby ice-core, unprecedented in coastal Antarctica.•Holocene glacial behavior generally mimics local atmospheric temperatures. Herbert Sound deglaciated by 10 ± 2.4 cal kyr BP.•Herbert Sound fully opened by 7.2 cal kyr BP during Mid Holocene warmth. A marine productivity event occurred 6.1 cal kyr BP.•Sea ice and ice rafting increased 2.5 cal kyr BP, marking onset of the Neoglacial.
•High-resolution conodont, foraminifer, biostratigraphy.•Magnetic reversal, magnetic susceptibility, chemical stratigraphy, and geochronology.•Upper Permian–Upper Triassic.•Guandao section, south ...China.
The chronostratigraphy of Guandao section has served as the foundation for numerous studies of the end-Permian extinction and biotic recovery in south China. Guandao section is continuous from the Permian–Triassic boundary to the Upper Triassic.
Conodonts enable broad delineation of stage and substage boundaries and calibration of foraminifer biostratigraphy as follows. Changhsingian–Griesbachian: first Hindeodus parvus, and first appearance of foraminifers Postcladella kalhori and Earlandia sp. Griesbachian–Dienerian: first Neospathodus dieneri, and last appearance of foraminifer P. grandis. Dienerian–Smithian: first Novispathodus waageni and late Dienerian first appearance of foraminifer Hoyenella ex gr. sinensis. Smithian–Spathian: first Nv? crassatus and last appearance of foraminifers Arenovidalina n. sp. and Glomospirella cf. vulgaris. Spathian–Aegean: first Chiosella timorensis and first appearance of foraminifer Meandrospira dinarica. Aegean–Bithynian: first Nicoraella germanica and first appearance of foraminifer Pilammina densa. Bithynian–Pelsonian: after last Neogondolella regalis, prior to first Paragondolella bulgarica and first appearance of foraminifer Aulotortus eotriasicus. Pelsonian–Illyrian: first Pg. excelsa and last appearance of foraminifers Meandrospira? deformata and Pilamminella grandis. Illyrian–Fassanian: first Budurovignathus truempyi, and first appearance of foraminifers Abriolina mediterranea and Paleolituonella meridionalis. Fassanian–Longobardian: first Bv. mungoensis and last appearance of foraminifer A. mediterranea. Longobardian–Cordevolian: first Quadralella polygnathiformis and last appearance of foraminifers Turriglomina mesotriasica and Endotriadella wirzi.
The section contains primary magnetic signature with frequent reversals occurring around the Permian–Triassic, Olenekian–Anisian, and Anisian–Ladinian boundaries. Predominantly normal polarity occurs in the lower Smithian, Bithynian, and Longobardian–Cordevolian. Predominantly reversed polarity occurs in the upper Griesbachian, Induan–Olenekian, Pelsonian and lower Illyrian. Reversals match well with the GPTS. Large amplitude carbon isotope excursions, attaining values as low as −2.9‰ δ13C and high as +5.7‰ δ13C, characterize the Lower Triassic and basal Anisian. Values stabilize around +2‰ δ13C through the Anisian to Carnian. Similar signatures have been reported globally. Magnetic susceptibility and synthetic gamma ray logs show large fluctuations in the Lower Triassic and an overall decline in magnitude of fluctuation through the Middle and Upper Triassic. The largest spikes in magnetic susceptibility and gamma ray, indicating greater terrestrial lithogenic flux, correspond to positive δ13C excursions. High precision U–Pb analysis of zircons from volcanic ash beds provide a robust age of 247.28±0.12Ma for the Olenekian–Anisian boundary at Guandao and an age of 251.985±0.097Ma for the Permian–Triassic boundary at Taiping. Together, the new U–Pb geochronology from the Guandao and Taiping sections suggest an estimated duration of 4.71±0.15Ma for the Early Triassic Epoch.
The geometry of the sea floor immediately beyond Antarctica's marine-terminating glaciers is a fundamental control on warm-water routing, but it also describes former topographic pinning points that ...have been important for ice-shelf buttressing. Unfortunately, this information is often lacking due to the inaccessibility of these areas for survey, leading to modelled or interpolated bathymetries being used as boundary conditions in numerical modelling simulations. At Thwaites Glacier (TG) this critical data gap was addressed in 2019 during the first cruise of the International Thwaites Glacier Collaboration (ITGC) project. We present more than 2000 km.sup.2 of new multibeam echo-sounder (MBES) data acquired in exceptional sea-ice conditions immediately offshore TG, and we update existing bathymetric compilations. The cross-sectional areas of sea-floor troughs are under-predicted by up to 40 % or are not resolved at all where MBES data are missing, suggesting that calculations of trough capacity, and thus oceanic heat flux, may be significantly underestimated. Spatial variations in the morphology of topographic highs, known to be former pinning points for the floating ice shelf of TG, indicate differences in bed composition that are supported by landform evidence. We discuss links to ice dynamics for an overriding ice mass including a potential positive feedback mechanism where erosion of soft erodible highs may lead to ice-shelf ungrounding even with little or no ice thinning. Analyses of bed roughnesses and basal drag contributions show that the sea-floor bathymetry in front of TG is an analogue for extant bed areas. Ice flow over the sea-floor troughs and ridges would have been affected by similarly high basal drag to that acting at the grounding zone today. We conclude that more can certainly be gleaned from these 3D bathymetric datasets regarding the likely spatial variability of bed roughness and bed composition types underneath TG. This work also addresses the requirements of recent numerical ice-sheet and ocean modelling studies that have recognised the need for accurate and high-resolution bathymetry to determine warm-water routing to the grounding zone and, ultimately, for predicting glacier retreat behaviour.
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