235 research outputs found
Light-Trap: A SiPM Upgrade for Very High Energy Astronomy and Beyond
With the development of the Imaging Atmospheric Cherenkov Technique (IACT),
Gamma-ray astronomy has become one of the most interesting and productive
fields of astrophysics. Current IACT telescope arrays (MAGIC, H.E.S.S, VERITAS)
use photomultiplier tubes (PMTs) to detect the optical/near-UV Cherenkov
radiation emitted due to the interaction of gamma rays with the atmosphere. For
the next generation of IACT experiments, the possibility of replacing the PMTs
with Silicon photomultipliers (SiPMs) is being studied. Among the main
drawbacks of SiPMs are their limited active area (leading to an increase in the
cost and complexity of the camera readout) and their sensitivity to unwanted
wavelengths. Here we propose a novel method to build a relatively low-cost
pixel consisting of a SiPM attached to a PMMA disc doped with a wavelength
shifter. This pixel collects light over a much larger area than a single
standard SiPM and improves sensitivity to near-UV light while simultaneously
rejecting background. We describe the design of a detector that could also have
applications in other fields where detection area and cost are crucial. We
present results of simulations and laboratory measurements of a pixel prototype
and from field tests performed with a 7-pixel cluster installed in a MAGIC
telescope camera.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Bexco, Busan, Korea. Id:81
Performance Evaluation of Three Silicon Photomultiplier Detector Modules within the MAGIC Telescopes PMT-based camera
MAGIC is a system of two imaging atmospheric Cherenkov telescopes (IACTs)
located on the Canary island of La Palma. Each telescope's imaging camera
consists of 1039 photomultiplier tubes (PMTs). We developed three detector
modules based on silicon photomultipliers (SiPMs) of seven pixels each that are
mechanically and electronically compatible with those used in the MAGIC camera.
These prototype modules are installed next to the PMTs in the imaging camera
and are operated in parallel. To achieve a similar active area per pixel we
used seven to nine SiPMs for producing a composite pixel. The SiPM signals
within one such pixel are actively summed up for retaining the fast signal
pulse shapes. Two different PCB designs are tested for thermal performance. We
present our simulations of Cherenkov and light of the night sky (LoNS)
responses. Based on those we calculate the signal-to-noise ratio (SNR) for this
imaging application. We compare our expectations with the measurements of one
of the SiPM-based detector modules.Comment: 18 pages, 4 figures, Proceedings of the 9th Conference on New
Developments In Photodetection (NDIP20), Troyes (France), 04-08 July 2022.
Published in Nuclear Instruments and Methods in Physics Research - section A
(NIM-A
Development of HPD Clusters for MAGIC-II
MAGIC-II is the second imaging atmospheric Cherenkov telescope of the MAGIC
observatory, which has recently been inaugurated on Canary island of La Palma.
We are currently developing a new camera based on clusters of hybrid photon
detectors (HPD) for the upgrade of MAGIC-II. The photon detectors feature a
GaAsP photocathode and an avalanche diode as electron bombarded anodes with
internal gain, and were supplied by Hamamatsu Photonics K.K. (R9792U-40). The
HPD camera with high quantum efficiency will increase the MAGIC-II sensitivity
and lower the energy threshold. The basic performance of the HPDs has been
measured and a prototype of an HPD cluster has been developed to be mounted on
MAGIC-II. Here we report on the status of the HPD cluster and the project of
eventually using HPD clusters in the central area of the MAGIC-II camera.Comment: Contribution to the 31st ICRC, Lodz, Poland, July 200
Band structure and optical properties of germanium sheet polymers
The band structure of H-terminated Ge sheet polymers is calculated using density-functional theory in the local density approximation and compared to the optical properties of epitaxial polygermyne layers as determined from reflection, photoluminescence, and photoluminescence excitation measurements. A direct band gap of 1.7 eV is predicted and a near resonant excitation of the photoluminescence is observed experimentally close to this energy
The major upgrade of the MAGIC telescopes, Part II: A performance study using observations of the Crab Nebula
MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in
the Canary island of La Palma, Spain. During summer 2011 and 2012 it underwent
a series of upgrades, involving the exchange of the MAGIC-I camera and its
trigger system, as well as the upgrade of the readout system of both
telescopes. We use observations of the Crab Nebula taken at low and medium
zenith angles to assess the key performance parameters of the MAGIC stereo
system. For low zenith angle observations, the standard trigger threshold of
the MAGIC telescopes is ~50GeV. The integral sensitivity for point-like sources
with Crab Nebula-like spectrum above 220GeV is (0.66+/-0.03)% of Crab Nebula
flux in 50 h of observations. The angular resolution, defined as the sigma of a
2-dimensional Gaussian distribution, at those energies is < 0.07 degree, while
the energy resolution is 16%. We also re-evaluate the effect of the systematic
uncertainty on the data taken with the MAGIC telescopes after the upgrade. We
estimate that the systematic uncertainties can be divided in the following
components: < 15% in energy scale, 11-18% in flux normalization and +/-0.15 for
the energy spectrum power-law slope.Comment: 21 pages, 25 figures, accepted for publication in Astroparticle
Physic
Rural–Urban Migration and Experience of Childhood Abuse in the Young Thai Population
Evidence suggests that certain migrant populations are at increased risk of abusive behaviors. It is unclear whether this may also apply to Thai rural–urban migrants, who may experience higher levels of psychosocial adversities than the population at large. The study aims to examine the association between migration status and the history of childhood sexual, physical, and emotional abuse among young Thai people in an urban community. A population-based cross-sectional survey was conducted in Northern Bangkok on a representative sample of 1052 young residents, aged 16–25 years. Data were obtained concerning: 1) exposures—migration (defined as an occasion when a young person, born in a more rural area moves for the first time into Greater Bangkok) and age at migration. 2) outcomes—child abuse experiences were assessed with an anonymous self report adapted from the Conflict Tactics Scales (CTS). There were 8.4%. 16.6% and 56.0% reporting sexual, physical, and emotional abuse, respectively. Forty six percent of adolescents had migrated from rural areas to Bangkok, mostly independently at the age of 15 or after to seek work. Although there were trends towards higher prevalences of the three categories of abuse among early migrants, who moved to Bangkok before the age of 15, being early migrants was independently associated with experiences of physical abuse (OR 1.9 95%CI 1.1–3.2) and emotional abuse (OR 2.0, 95%CI 1.3–3.0) only. Our results suggest that rural–urban migration at an early age may place children at higher risk of physical and emotional abuse. This may have policy implications for the prevention of childhood abuse particularly among young people on the move
Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy
Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA
Global urban environmental change drives adaptation in white clover.
Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale
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