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Spectral resolution in pixel detectors with single photon processing
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.ORCID iD: 0000-0002-8325-5177
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.ORCID iD: 0000-0002-5619-409X
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
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2013 (English)In: Proceedings of SPIE - The International Society for Optical Engineering, SPIE - International Society for Optical Engineering, 2013, Art. no. 88520O- p.Conference paper (Other academic)
Abstract [en]

Pixel detectors based on photon counting or single photon processing readout are becoming popular for spectral X-ray imaging. The detector is based on deep submicron electronics with functions to determine the energy of each individual photon in every pixel. The system is virtually noiseless when it comes to the number of the detected photons. However noise and variations in system parameters affect the determination of the photon energy. Several factors affect the energy resolution in the system. In the readout electronics the most important factors are the threshold dispersion, the gain variation and the electronic noise. In the sensor contributions come from charge sharing, variations in the charge collection efficiency, leakage current and the statistical nature of the charge generation, as described by the Fano factor. The MEDIPIX technology offers a powerful tool for investigating these effects since energy spectra can be captured in each pixel. In addition the TIMEPIX chip, when operated in Time over Threshold mode, offers an opportunity to analyze individual photon interactions, thus addressing charge sharing and fluorescence. Effects of charge sharing and the properties of charge summing can be investigated using MEDIPIX3RX. Experiments are performed using both Si and CdTe detectors. In this paper we discuss the various contributions to the spectral noise and how they affect detector response. The statements are supported with experimental data from MEDIPIX-type detectors.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2013. Art. no. 88520O- p.
Series
Proceedings of SPIE, ISSN 0277-786X ; 8852
Keyword [en]
Pixel detectors, single photon processing, X-ray
National Category
Accelerator Physics and Instrumentation
Identifiers
URN: urn:nbn:se:miun:diva-21069DOI: 10.1117/12.2023983ISI: 000326643800014Scopus ID: 2-s2.0-84886996985Local ID: STCISBN: 978-081949702-4 (print)OAI: oai:DiVA.org:miun-21069DiVA: diva2:688220
Conference
SPIE Conference on Hard X-Ray, Gamma-Ray and Neutron Detector Physics XV; San Diego, CA; United States; 26 August 2013 through 28 August 2013; Code 100563
Available from: 2014-01-16 Created: 2014-01-16 Last updated: 2016-11-10Bibliographically approved
In thesis
1. Monte Carlo and Charge Transport Simulation of Pixel Detector Systems
Open this publication in new window or tab >>Monte Carlo and Charge Transport Simulation of Pixel Detector Systems
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is about simulation of semiconductor X-ray and particledetectors. The simulation of a novel coating for solid state neutrondetectors is discussed as well as the implementation of a simulationframework for hybrid pixel detectors.Today’s most common thermal neutron detectors are proportionalcounters, that use 3He gas in large tubes or multi wire arrays. Globalnuclear disarmament and the increase in use for homeland securityapplications has created a shortage of the gas which poses a problemfor neutron spallation sources that require higher resolution and largersensors. In this thesis a novel material and clean room compatible pro-cess for neutron conversion are discussed. Simulations and fabricationhave been executed and analysed in measurements. It has been proventhat such a device can be fabricated and detect thermal neutrons.Spectral imaging hybrid pixel detectors like the Medipix chipare the most advanced imaging systems currently available. Thesechips are highly sophisticated with several hundreds of transistors perpixel to enable features like multiple thresholds for noise free photoncounting measurements, spectral imaging as well as time of arrivalmeasurements. To analyse and understand the behaviour of differentsensor materials bonded to the chip and to improve development offuture generations of the chip simulations are necessary. Generally, allparts of the detector system are simulated independently. However, itis favourable to have a simulation framework that is able to combineMonte Carlo particle transport, charge transport in the sensor as wellas analogue and digital response of the pixel read-out electronics. Thisthesis aims to develop such a system that has been developed withGeant4 and analytical semiconductor and electronics models. Further-more, it has been verified with data from measurements with severalMedipix and Timepix sensors as well as TCAD simulations.Results show that such a framework is feasible even for imagingsimulations. It shows great promise to be able to be extended withfuture pixel detector designs and semiconductor materials as well asneutron converters to aim for next generation imaging devices.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2015. 95 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 215
Keyword
Monte Carlo Simulation, TCAD, pixel detectors, Medipix, Timepix, Finite Element Simulation
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:miun:diva-24763 (URN)STC (Local ID)978-91-88025-06-7 (ISBN)STC (Archive number)STC (OAI)
Public defence
2015-04-08, M102, Mittuniversitetet, Holmgatan 10, Sundsvall, 10:00 (English)
Opponent
Supervisors
Available from: 2015-03-31 Created: 2015-03-31 Last updated: 2016-12-23Bibliographically approved
2. Advanced X-ray Detectors for Industrial and Environmental Applications
Open this publication in new window or tab >>Advanced X-ray Detectors for Industrial and Environmental Applications
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The new generation of X-ray free electron laser sources arecapable of producing light beams with billion times higherpeak brilliance than that of the best conventional X-ray sources.This advancement motivates the scientific community to pushforward the detector technology to its limit, in order to de-sign photon detectors which can cope with the extreme fluxgenerated by the free electron laser sources. Sophisticated ex-periments like deciphering the atomic details of viruses, filmingchemical reactions or investigating the extreme states of matterrequire detectors with high frame rate, good spatial resolution,high dynamic range and large active sensor area. The PERCI-VAL monolithic active pixel sensor is being developed by aninternational group of scientists in collaboration to meet theaforementioned detector requirements within the energy rangeof 250 eV to 1 keV, with a quantum efficiency above 90%.In this doctoral researchwork, Monte Carlo algorithm basedGeant4 and finite element method based Synopsys SentaurusTCADtoolkits have been used to simulate, respectively, theX-rayenergy deposition and the charge sharing in PERCIVAL. Energydeposition per pixel and charge sharing between adjacent pixelsat different energies have been investigated and presented.Novel methods for industrial and environmental applica-tions of some commercially available X-ray detectors have beendemonstrated. Quality inspection of paperboards by resolv-ing the layer thicknesses and by investigating orientation ofthe cellulose fibres have been performed using spectroscopicand phase-contrast X-ray imaging. It was found that, usingphase-contrast imaging it is possible to set burn-out like qualityindex on paperboards non-destructively. X-ray fluoroscopicmeasurements have been conducted in order to detect Cr inwater. This method can be used to detect Cr and other toxicelements in leachate in landfills and other waste dumping sites.

Abstract [sv]

Acceleratorbaserade röntgenkällor utvecklas ständigt, dessakan producera röntgenstrålning med miljarder gånger så högeffekttäthet som de starkaste konventionella röntgenkällorna.Därför finns en vetenskaplig utmaning att utveckla röntgende-tektorer som inte förstörs i de extrema flöden som genereras avdessa röntgenkällor. De visioner som finns för de nya källornaär t.ex.; att avbilda detaljer av virus ner på atomnivå, att filmakemiska reaktioner eller att undersöka extrema tillstånd hos ma-teria. Dessa typer av experiment kräver röntgendetektorer medhög bildhastighet, hög spatial upplösning och stort intensitets-omfång och stor aktiv sensoryta. Detektorsystemet PERCIVALsom bygger på aktiva pixlar med energiupplösning utvecklasinom ett internationellt vetenskapligt samarbetsprojekt. Må-let är att uppfylla detektorspecifikationerna för de nämndaexperimenten inom energiområdet 250 eV till 1 keV, med enkvantverkningsgrad över 90 %.I föreliggande vetenskapliga avhandlingsarbete har simule-ringar av energideponering i PERCIVAL-detektorn genomförtsbaserat på Monte Carlo-algoritmer och simuleringar av ladd-ningsdelning mellan pixlar har simulerats med hjälp av finitaelementmetoden. Därmed har energideponeringen per pixeloch laddningsdelningen mellan närliggande pixlar vid olikaenergier kunnat utredas och presenteras.I avhandlingen demonstreras nya lovande metoder för in-dustriella applikationer och miljöövervakning,därkommersiellttillgängliga röntgendetektorer kan användas. Kvalitetsövervak-ning av kartongtillverkning genom att mäta bestrykningstjock-lek och fiberorientering kan realiseras med energiupplöstaröntgenbilder eller faskontrastbilder i röntgenområdet. Det kankonstateras att med icke-förstörande provning, genom faskon-trastbilder, kan kvalitetsindexvärlden erhållas på samma sättsom kvalitetsindex kan erhållas från ”burn-out”-mätningar.Spektroskopiska mätningar av röntgenflourescens har genom-förts för att detektera krom (Cr) i vatten. Metodik för att detek-tera krom och andra giftiga metaller i lakvatten från deponioch annan lagring för giftigt avfall har utarbetats.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2016. 159 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 253
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-29264 (URN)STC (Local ID)978-91-88025-84-5 (ISBN)STC (Archive number)STC (OAI)
Public defence
2016-12-01, M108, Sundsvall, 10:15 (English)
Opponent
Supervisors
Available from: 2016-11-10 Created: 2016-11-10 Last updated: 2017-06-30Bibliographically approved

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