44 research outputs found
The lead-glass electromagnetic calorimeters for the magnetic spectrometers in Hall C at Jefferson Lab
The electromagnetic calorimeters of the various magnetic spectrometers in
Hall C at Jefferson Lab are presented. For the existing HMS and SOS
spectrometers design considerations, relevant construction information, and
comparisons of simulated and experimental results are included. The energy
resolution of the HMS and SOS calorimeters is better than , and pion/electron () separation of about 100:1 has been
achieved in energy range 1 -- 5 GeV. Good agreement has been observed between
the experimental and simulated energy resolutions, but simulations
systematically exceed experimentally determined suppression factors by
close to a factor of two. For the SHMS spectrometer presently under
construction details on the design and accompanying GEANT4 simulation efforts
are given. The anticipated performance of the new calorimeter is predicted over
the full momentum range of the SHMS. Good electron/hadron separation is
anticipated by combining the energy deposited in an initial (preshower)
calorimeter layer with the total energy deposited in the calorimeter.Comment: 22 pages, 33 figure
Scintillator ageing of the T2K near detectors from 2010 to 2021
The T2K experiment widely uses plastic scintillator as a target for neutrino interactions and an active medium for the measurement of charged particles produced in neutrino interactions at its near detector complex. Over 10 years of operation the measured light yield recorded by the scintillator based subsystems has been observed to degrade by 0.9â2.2% per year. Extrapolation of the degradation rate through to 2040 indicates the recorded light yield should remain above the lower threshold used by the current reconstruction algorithms for all subsystems. This will allow the near detectors to continue contributing to important physics measurements during the T2K-II and Hyper-Kamiokande eras. Additionally, work to disentangle the degradation of the plastic scintillator and wavelength shifting fibres shows that the reduction in light yield can be attributed to the ageing of the plastic scintillator. The long component of the attenuation length of the wavelength shifting fibres was observed to degrade by 1.3â5.4% per year, while the short component of the attenuation length did not show any conclusive degradation
Formation of Iron Silicides Under Graphene Grown on the Silicon Carbide Surface
The formation of iron silicide thin films under graphene grown on the silicon carbide surface is investigated. The thin films are synthesized by consecutive intercalation of iron and silicon atoms into the graphene. Experiments are carried out in situ in ultrahigh vacuum. The elemental composition and chemical state of the surface of prepared samples and their atomic structure are determined by low energy electron diffraction and high resolution X ray photoelectron spectroscopy using synchrotron radiation. The thickness of deposited iron and silicon layers varies in the range of 0.1 2 nm, and the sample annealing temperature is varied from room temperature to 600 C. We show that intercalation of silicon into the graphene Fe SiC system leads to the formation of a layer of Fe Si solid solution coated with the surface silicide Fe3Si. The films are effectively protected by graphene from exposure to ambient environment, which opens possibilities for their practical applicatio
Dissolved organic carbon loss from Yedoma permafrost amplified by ice wedge thaw
Pleistocene Yedoma permafrost contains nearly a third of all organic matter (OM) stored in circum-arctic
permafrost and is characterized by the presence of massive ice wedges. Due to its rapid formation by
sediment accumulation and subsequent frozen storage, Yedoma OM is relatively well preserved and highly
biologically available (biolabile) upon thaw. A better understanding of the processes regulating Yedoma
degradation is important to improve estimates of the response and magnitude of permafrost carbon
feedbacks to climate warming. In this study, we examine the composition of ice wedges and the influence of
ice wedge thaw on the biolability of Yedoma OM. Incubation assays were used to assess OM biolability,
fluorescence spectroscopy to characterize the OM composition, and potential enzyme activity rates to
examine the controls and regulation of OM degradation.We show that increasing amounts of ice wedge melt
water in Yedoma-leached incubations enhanced the loss of dissolved OM over time. This may be attributed
to the presence of low-molecular weight compounds and low initial phenolic content in the OM of ice
wedges, providing a readily available substrate that promotes the degradation of Yedoma OC. The physical
vulnerability of ice wedges upon thaw (causing irreversible collapse), combined with the composition of ice
wedge-engrained OM (co-metabolizing old OM), underlines the particularly strong potential of Yedoma to
generate a positive feedback to climate warming relative to other forms of non-ice wedge permafrost