794 research outputs found
3D Simulation of Electron and Ion Transmission of GEM-based Detectors
Time Projection Chamber (TPC) has been chosen as the main tracking system in
several high-flux and high repetition rate experiments. These include on-going
experiments such as ALICE and future experiments such as PANDA at FAIR and ILC.
Different activities were carried out on the adoption
of Gas Electron Multiplier (GEM) as the gas amplification stage of the
ALICE-TPC upgrade version. The requirement of low ion feedback has been
established through these activities. Low ion feedback minimizes distortions
due to space charge and maintains the necessary values of detector gain and
energy resolution. In the present work, Garfield simulation framework has been
used to study the related physical processes occurring within single, triple
and quadruple GEM detectors. Ion backflow and electron transmission of
quadruple GEMs, made up of foils with different hole pitch under different
electromagnetic field configurations (the projected solutions for the ALICE
TPC) have been studied. Finally a new triple GEM detector configuration with
low ion backflow fraction and good electron transmission properties has been
proposed as a simpler GEM-based alternative suitable for TPCs for future
collider experiments
Development of neutron and X-ray imaging detectors based on MHSP
Doutoramento em FÃsicaA Micro-Hole & Strip Plate (MHSP) é uma microestrutura desenvolvida recentemente em instituições universitárias portuguesas. Neste trabalho, o seu desempenho como detector para imagiologia é explorado, tendo como objectivo a imagiologia não só de neutrões, mas também de raios X. A aplicação do método da divisão resistiva de carga é aplicada a uma MHSP especialmente desenhada para sensibilidade em posição. Várias abordagens em termos da electrónica de aquisição de sinal são testadas, sem perder de vista a relação desempenho-preço. Resoluções espaciais abaixo de 1 mm foram obtidas com a MHSP a operar em xénon e tetrafluorometano, com um sistema de detecção a um preço modesto quando comparado com as alternativas, e apropriado para inúmeras aplicações em imagiologia de neutrões e de raios X.The Micro-Hole & Strip Plate (MHSP) is a Micropattern Gaseous Detector developed recently in Portuguese institutions. In this work, its performance as a imaging detector is characterised, aiming neutron imaging, but also with results in X-ray imaging. The application of the method of resistive charge division is used in a MHSP specially designed for position sensitivity. Several different electronic approaches for signal collection are tested, always taking into account the performance-price ratio. Position resolutions below 1 mm were achieved with the MHSP operating in xenon and in tetrafluoromethane, in a very cost effective detector setup, suitable for many applications in neutron and X-ray imaging
Ion backflow studies with a triple-GEM stack with increasing hole pitch
Gas Electron Multipliers have undergone a very consistent development since
their invention in 1997. Their production procedures have been tuned in such a
way that nowadays it is possible to produce foils with areas of the order of
the square meter that can operate at a reasonable gain, uniform over large
areas and with a good stability in what concerns electrical discharges. For the
third run of LHC, they will be included in the CMS and ALICE experiments after
significant upgrades of the detectors, confirming that these structures are
suitable for very large experiments. In the special case of Time Projection
Chambers, the ion backflow and the energy resolution are sensitive issues that
must be addressed and the GEM has shown to be able to deal with both of them.
In this work, a stack of three GEMs with different pitches has been studied
as a possible future approach for ion-backflow suppression to be used in TPCs
and other detection concepts. With this approach, an ion backflow of 1 % with
an energy resolution of 12 % at 5.9 keV has been achieved with the detector
operating in an Ar/CO2 (90/10) mixture at a gain of ~ 2000.Comment: 15 pages, 11 figure
Feeding inhibition in the soil collembolan Folsomia candida as an endpoint for the estimation of organic waste ecotoxicity
Despite the increasing quantities of organic wastes that are being reused in soils, there are few studies that focus on the selection of bioassays for the ecotoxicological risk assessment of organic wastes to soils. In the present study, differences in feeding inhibition in the soil collembolan Folsomia candida were evaluated as an ecotoxicological endpoint for the assessment of risk to soils amended with polluted organic wastes. Seven organic wastes (dewatered sewage sludges, thermally dried sewage sludges, composted sewage sludges, and a thermally dried pig slurry) were tested. These wastes had different origins, treatments, and pollutant burdens, and were selected as a representative sample of the wide variety of wastes currently generated. A clear dose response was observed for this parameter, with an increase in percentage of individual feeding inhibition with increased doses of organic wastes. More significantly, feeding inhibition correlated highly with mortality and reproduction inhibition in the different wastes. Composted sludges displayed the lowest toxicity, followed by thermally dried sludge and dewatered sludge. Thermally dried pig slurry showed the highest toxicity for feeding, with lower median effective concentration (EC50) values than the lowest dose tested. Among waste physicochemical parameters and pollutants, low organic matter stability appeared to be the main predictor of potential adverse effects on soil fauna, because it correlated significantly with feeding inhibition and mortality. Furthermore, feeding inhibition tests were run over a short exposure time (less than 7 d), which, together with the results obtained, makes this bioassay a good screening tool for organic waste toxicity
Micro-Hole and Strip Plate (MHSP) operation in CF4
The Micro-Hole and Strip Plate (MHSP) is a hybrid electron multiplier which combines the working principles of a Gas Electron Multiplier (GEM) and a Micro-Strip Gas Counter (MSGC). The compact double stage electron multiplication processes found in the MHSP enables the realisation of higher gas gain than the lone GEM operation. Thermal neutron detection using gas detectors involves the use of gas with another suitable stopping gas, operated at elevated pressure to confine the products of the neutron- reaction. It is, however, well known that the gain of GEMs drops too sharply with increasing chamber pressure.http://www.sciencedirect.com/science/article/B6TJM-4NS2G9V-D/1/497af6476b376b1c2f407a3fa7ff735
Beam Studies of the Segmented Resistive WELL: a Potential Thin Sampling Element for Digital Hadron Calorimetry
Thick Gas Electron Multipliers (THGEMs) have the potential of constituting
thin, robust sampling elements in Digital Hadron Calorimetry (DHCAL) in future
colliders. We report on recent beam studies of new single- and
double-THGEM-like structures; the multiplier is a Segmented Resistive WELL
(SRWELL) - a single-faced THGEM in contact with a segmented resistive layer
inductively coupled to readout pads. Several 1010 cm configurations
with a total thickness of 5-6 mm (excluding electronics) with 1 cm pads
coupled to APV-SRS readout were investigated with muons and pions. Detection
efficiencies in the 98 range were recorded with average pad-multiplicity of
1.1. The resistive anode resulted in efficient discharge damping, with
potential drops of a few volts; discharge probabilities were for
muons and for pions in the double-stage configuration, at rates
of a few kHz/cm. Further optimization work and research on larger detectors
are underway.Comment: Presented at the Vienna Conference on Instrumentation,
February 2013 and submitted to its proceeding
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