The analysis of ring images produced by muons in an Imaging Atmospheric Cherenkov Telescope (IACT) provides a powerful and precise method to calibrate the IACT optical throughput and monitor its ...optical point-spread function (PSF). First proposed by the Whipple Collaboration in the early 1990s, this method has been refined by the so-called second generation of IACT experiments: H.E.S.S., MAGIC, and VERITAS. We review here the progress made with these instruments and investigate the applicability of the method as the primary throughput calibration method for the different telescope types forming the future Cherenkov Telescope Array (CTA). We find several additional systematic effects not yet taken into account by previous authors and propose several new analytical methods to include these in the analysis. Slight modifications in hardware and analysis need to be made to ensure that such a calibration works as accurately as required for the CTA. We derive analytic estimates for the expected muon data rates for optical throughput calibration, camera pixel flat-fielding, and monitoring of the optical PSF. The achievable statistical and systematic uncertainties of the method are also assessed.
Silicon photomultipliers (SiPMs) are now replacing photomultiplier tubes where low voltage operations, compactness, and cost per channel are important. However, optical crosstalk (OCT) is still one ...of the major disadvantages of SiPMs since it increases accidental triggers and degrades the accuracy of photon counting. Previously, we reported that OCTs can be suppressed by either thicker or no protection resin coating. Although no resin coating heavily suppresses OCTs, we still observe some OCTs at a few % levels. In this study, we have investigated the properties of OCTs and delayed OCTs for several types of SiPMs with different device sizes, cell sizes, and resin coating thickness. We observe that delayed OCTs have very similar properties compared with OCTs with no resin coating. Furthermore, we find that the sizable amount of delayed OCTs is overlapping with the original pulse and may be treated as OCTs when the delay is less than 8 ns in our analysis. Since the properties and rate of overlaps of delayed OCTs match those of OCTs with no resin coating, we conclude that the remaining OCTs for SiPMs with no coating can be fully explained by overlaps of delayed OCTs.
ABSTRACT A study of the interstellar medium (ISM) and cosmic rays (CRs) using Fermi Large Area Telescope (LAT) data, in a region encompassing the nearby molecular clouds MBM 53, 54, and 55 and a ...far-infrared loop-like structure in Pegasus, is reported. By comparing the Planck dust thermal emission model with Fermi-LAT γ-ray data, it was found that neither the dust radiance (R) nor the dust opacity at 353 GHz (τ353) was proportional to the total gas column density N(Htot) primarily because N(Htot)/R and N(Htot)/τ353 depend on the dust temperature (Td). The N(Htot) distribution was evaluated using γ-ray data by assuming the regions of high Td to be dominated by optically thin atomic hydrogen ( ) and by employing an empirical linear relation of N(Htot)/R to Td. It was determined that the mass of the gas not traced by the 21 cm or 2.6 mm surveys is ∼25% of the mass of in the optically thin case and is larger than the mass of the molecular gas traced by carbon monoxide by a factor of up to 5. The measured γ-ray emissivity spectrum is consistent with a model based on CR spectra measured at the Earth and a nuclear enhancement factor of ≤1.5. It is, however, lower than local emissivities reported by previous Fermi-LAT studies employing different analysis methods and assumptions on ISM properties by 15%-20% in energies below a few GeV, even if we take account of the statistical and systematic uncertainties. The origin of the discrepancy is also discussed.
An accurate estimate of the interstellar gas density distribution is crucial to understanding the interstellar medium (ISM) and Galactic cosmic rays (CRs). To comprehend the ISM and CRs in a local ...environment, a study of the diffuse γ-ray emission in a midlatitude region of the third quadrant was performed. The γ-ray data in the 0.1-25.6 GeV energy range of the Fermi Large Area Telescope (LAT) and other interstellar gas tracers such as the HI4PI survey data and the Planck dust thermal emission model were used, and the northern and southern regions were analyzed separately. The variation of the dust emission with the total neutral gas column density was studied in high dust temperature areas, and the / ratio was calibrated using γ-ray data under the assumption of a uniform CR intensity in the studied regions. The measured integrated γ-ray emissivities above 100 MeV are and in the northern and southern regions, respectively, supporting the existence of a uniform CR intensity in the vicinity of the solar system. While most of the gas can be interpreted to be with a spin temperature of or higher, an area dominated by optically thick with was identified.
Saltpetre constitutes one of the major ingredients of gunpowder, which was a driving force during the political changes in late medieval to early modern times in Japan. Two types of model saltpetre ...mineralization are studied. One represents efflorescent saltpetre formed as the byproduct of indigo dye manufacture, whereas the second is anthropogenic, derived from relict nitre‐beds. Here, oxygen and nitrogen isotopic analysis, as expressed by δ18O and δ15N notations, is applied. The calculated δ18O values for ambient water, responsible for the microbial‐mediated oxidation of ammonium into oxygen in nitrates, tended to have higher ranges than average local meteoric waters of the relevant regions. An overall trend could be seen, showing the apparent positive nitrogen isotopic fractionation during the microbial transformation from initial organic nitrogen into nitrate product. Dual isotopic analysis for industrial nitrates provides a useful tool for investigation of the provenance of historic gunpowder. Present anthropogenic saltpetre involves positive control over temperature–moisture regimes and oxygen fugacity during formation, the process being distinctive from those prevailed in British India and other European countries.
All camera designs for Small-Sized telescopes (SSTs) proposed for the Cherenkov Telescope Array (CTA) utilize silicon photomultipliers (SiPM) as their baseline photon sensor technology. The ...dual-mirror SST (SST-2M) has a smaller plate scale (i.e. image size) than the single-mirror SST, allowing it to employ 2,000 square SiPMs with pixel sizes of approximately 6 mm, close to the mainstream SiPM sizes.
In CTA, the night sky background level of typically ∼25 Mcounts/s/pixel (>100 Mcounts/s/pixel at maximum) places severe constraints on the trigger capability due to accidental coincidence on neighboring pixels. In order to suppress such events, it is necessary to reduce optical crosstalk, a mechanism whereby a single optical photon can produce multiple avalanches in the SiPM, while keeping good photon detection efficiency. These are, in general, contradicting requirements.
In this manuscript, we report on characterization of a variety of SiPM technologies for SST-2M cameras and compare results obtained at different participating institutions. We assess the harmonization of results and discuss the likely performance that will be achieved for the first production cameras.
•Scaling of SiPM parameters with known factors helps to find other unknown factors.•Lower breakdown SiPM yields better photon detection efficiencies at lower crosstalk.•The SiPM optical crosstalk can be reduced by thicker protection coating above 100 μm.•Lower breakdown SiPM yields better photon detection efficiencies at lower crosstalk.
In the context of amplitude-integrated electroencephalography (aEEG), the term 'sleep-wake cycling' (SWC), which is frequently used by clinicians and researchers, should be changed to 'cyclicity'. ...SWC is a technical term that refers to the biological pattern of alternating sleeping and waking states, which is difficult to define with only aEEG and no physical parameters. Additionally, the absence of cyclicity on aEEG is a more robust reflection of the sequence of the suppressed background patterns of an aEEG following cerebral injury or dysfunction than are sleep/wake states.
Background: Non-missile traumatic brain injury (nmTBI) without macroscopically detectable lesions often results in cognitive impairments that negatively affect daily life. Aim: To identify abnormal ...white matter projections in patients with nmTBI with cognitive impairments using diffusion tensor magnetic resonance imaging (DTI). Methods: DTI scans of healthy controls were compared with those of 23 patients with nmTBI who manifested cognitive impairments but no obvious neuroradiological lesions. DTI was comprised of fractional anisotropy analysis, which included voxel-based analysis and confirmatory study using regions of interest (ROI) techniques, and magnetic resonance tractography of the corpus callosum and fornix. Results: A decline in fractional anisotropy around the genu, stem and splenium of the corpus callosum was shown by voxel-based analysis. Fractional anisotropy values of the genu (0.47), stem (0.48), and splenium of the corpus callosum (0.52), and the column of the fornix (0.51) were lower in patients with nmTBI than in healthy controls (0.58, 0.61, 0.62 and 0.61, respectively) according to the confirmatory study of ROIs. The white matter architecture in the corpus callosum and fornix of patients with nmTBI were seen to be coarser than in the controls in the individual magnetic resonance tractography. Conclusions: Disruption of the corpus callosum and fornix in patients with nmTBI without macroscopically detectable lesions is shown. DTI is sensitive enough to detect abnormal neural fibres related to cognitive dysfunction after nmTBI.
Front-end electronics of the Compact High Energy Camera Leach, S.A.; Lapington, J.S.; Ross, D. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2020, Letnik:
952
Journal Article
Recenzirano
Odprti dostop
The Compact High Energy Camera is a focal plane camera designed for two mirror Schwarzschild–Couder design imaging air Cherenkov telescopes such as the SST-2M variants on the Cherenkov Telescope ...Array. It utilises a 2048-pixel array of silicon photomultipliers arranged in thirty-two 8 x 8 pixel2 tiles. Each detector tile is instrumented with a front-end electronics module designed to provide single photon counting with sub-nanosecond timing, full-waveform digitisation and event triggering capabilities based around TARGET ASICs. Performance results including triggering, digitiser noise, signal crosstalk, linearity and dynamic range from initial laboratory tests have been collated and are presented.
•Optimised readout electronics for imaging air Cherenkov telescope cameras with SiPMs.•Triggering performance improved to <3 mV compared to previous of >20 mV.•Typical measured noise <1 mV RMS across whole 64 channel module.•Coincident crosstalk <1% between all channels across each circuit board.•Calibration technique to normalise and linearise channel signal response.
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