Drift parameters optimization of a TPC polarimeter: a simulation study

Time Projection Chamber (TPC) based X-ray polarimeters using Gas Electron Multiplier (GEM) are currently being developed to make sensitive measurement of polarization in 2-10 keV energy range. The emission direction of the photoelectron ejected via photoelectric effect carries the information of the polarization of the incident X-ray photon. Performance of a gas based polarimeter is affected by the operating drift parameters such as gas pressure, drift field and drift-gap. We present simulation studies carried out in order to understand the effect of these operating parameters on the modulation factor of a TPC polarimeter. Models of Garfield are used to study photoelectron interaction in gas and drift of electron cloud towards GEM. Our study is aimed at achieving higher modulation factors by optimizing drift parameters. Study has shown that Ne/DME (50/50) at lower pressure and drift field can lead to desired performance of a TPC polarimeter

Study of electron focusing in thick GEM based photon detectors using semitransparent photocathodes

The detection efficiency of a GEM based UV sensitive gaseous photomultiplier (GPM) depends on the focusing of electrons from the drift gap to the GEM aperture. We have studied the effect of drift parameters on the efficiency of electron focusing into Thick GEM (THGEM) holes in a GPM with semitransparent UV photoconverter. This study comprises simulation of electron focusing into THGEM holes using GARFIELD for different Ar and Ne based gas mixtures and experimental investigations of the same with P10 gas mixture. (c) 2013 Elsevier B.V. All rights reserved

Performance study of a cesium iodide photocathode-based UV photon detector in Ar/CH4 mixture

The detection efficiency of a gaseous photomultiplier depends on the photocathode quantum efficiency and the extraction efficiency of photoelectrons into the gas. In this paper we have studied the performance of an UV photon detector with P10 gas in which the extraction efficiency can reach values near to those in vacuum operated devices. Simulations have been done to compare the percentage of photoelectrons backscattered in P10 gas as well as in the widely used neon-based gas mixture. The performance study has been carried out using a single stage thick gas electron multiplier (THGEM). The electron pulses and electron spectrum are recorded under various operating conditions. Secondary effects prevailing in UV photon detectors like photon feedback are discussed and its effect on the electron spectrum under different operating conditions is analyzed. (C) 2014 Chinese Laser Pres

Simulation studies on Performance parameters of a TPC Polarimeter

X-ray polarimeters based on Time Projection Chamber (TPC) geometry are currently being studied and developed to make sensitive measurement of polarization in 2-10keV energy range. TPC soft X-ray polarimeters exploit the fact that emission direction of the photoelectron ejected via photoelectric effect in a gas proportional counter carries the information of the polarization of the incident X-ray photon. Operating parameters such as pressure, drift field and drift-gap affect the performance of a TPC polarimeter. Simulations presented here showcase the effect of these operating parameters on the modulation factor of the TPC polarimeter. Models of Garfield are used to study photoelectron interaction in gas and drift of electron cloud towards Gas Electron Multiplier (GEM). The emission direction is reconstructed from the image and modulation factor is computed. Our study has shown that Ne/DME (50/50) at lower pressure and drift field can be used for a TPC polarimeter with modulation factor of 50-65%

Study on the detection efficiency of gaseous photomultipliers

Efficient photon detection in gaseous photomultipliers require maximum photoelectron yield from the photocathode surface and also detection of them. In this work we have investigated the parameters that affect the photoelectron yield from the photocathode surface and methods to improve them thus ensuring high detection efficiency of the gaseous photomultiplier. The parameters studied are the electric field at the photocathode surface, surface properties of photocathode and pressure of gas mixture inside the gaseous photomultiplier. It was observed that optimized electric field at the photocathode ensures high detection efficiency. Lower pressure of filled gas increases the photoelectron yield from the photocathode surface but reduces the focusing probability of electrons inside the electron multiplier. Also evacuation for longer duration before gas filling increases the photoelectron yield

Investigation of Burkholderia cepacia complex in septicaemic patients in a tertiary care hospital, India

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Multidimensional dynamic healthcare personnel (HCP)-centric model from a low-income and middle-income country to support and protect COVID-19 warriors: a large prospective cohort study

Objectives Healthcare personnel (HCP) are at an increased risk of acquiring COVID-19 infection especially in resource-restricted healthcare settings, and return to homes unfit for self-isolation, making them apprehensive about COVID-19 duty and transmission risk to their families. We aimed at implementing a novel multidimensional HCP-centric evidence-based, dynamic policy with the objectives to reduce risk of HCP infection, ensure welfare and safety of the HCP and to improve willingness to accept and return to duty.Setting Our tertiary care university hospital, with 12 600 HCP, was divided into high-risk, medium-risk and low-risk zones. In the high-risk and medium-risk zones, we organised training, logistic support, postduty HCP welfare and collected feedback, and sent them home after they tested negative for COVID-19. We supervised use of appropriate personal protective equipment (PPE) and kept communication paperless.Participants We recruited willing low-risk HCP, aged <50 years, with no comorbidities to work in COVID-19 zones. Social distancing, hand hygiene and universal masking were advocated in the low-risk zone.Results Between 31 March and 20 July 2020, we clinically screened 5553 outpatients, of whom 3012 (54.2%) were COVID-19 suspects managed in the medium-risk zone. Among them, 346 (11.4%) tested COVID-19 positive (57.2% male) and were managed in the high-risk zone with 19 (5.4%) deaths. One (0.08%) of the 1224 HCP in high-risk zone, 6 (0.62%) of 960 HCP in medium-risk zone and 23 (0.18%) of the 12 600 HCP in the low-risk zone tested positive at the end of shift. All the 30 COVID-19-positive HCP have since recovered. This HCP-centric policy resulted in low transmission rates (<1%), ensured satisfaction with training (92%), PPE (90.8%), medical and psychosocial support (79%) and improved acceptance of COVID-19 duty with 54.7% volunteering for re-deployment.Conclusion A multidimensional HCP-centric policy was effective in ensuring safety, satisfaction and welfare of HCP in a resource-poor setting and resulted in a willing workforce to fight the pandemic