| 1. |
- An, S., et al.
(författare)
-
Characterization of micro pore optics for full-field X-ray fluorescence imaging
- 2023
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 18:1
-
Tidskriftsartikel (refereegranskat)abstract
- Elemental mapping images can be achieved through step scanning imaging using pinhole optics or micro pore optics (MPO), or alternatively by full-field X-ray fluorescence imaging (FF-XRF). X-ray optics for FF-XRF can be manufactured with different micro-channel geometries such as square, hexagonal or circular channels. Each optic geometry creates different imaging artefacts. Square-channel MPOs generate a high intensity central spot due to two reflections via orthogonal channel walls inside a single channel, which is the desirable part for image formation, and two perpendicular lines forming a cross due to reflections in one plane only. Thus, we have studied the performance of a square-channel MPO in an FF-XRF imaging system. The setup consists of a commercially available MPO provided by Photonis and a Timepix3 readout chip with a silicon detector. Imaging of fluorescence from small metal particles has been used to obtain the point spread function (PSF) characteristics. The transmission through MPO channels and variation of the critical reflection angle are characterized by measurements of fluorescence from copper and titanium metal fragments. Since the critical angle of reflection is energy dependent, the cross-arm artefacts will affect the resolution differently for different fluorescence energies. It is possible to identify metal fragments due to the form of the PSF function. The PSF function can be further characterized using a Fourier transform to suppress diffuse background signals in the image.
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| 2. |
- An, Siwen, et al.
(författare)
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Full-field X-ray fluorescence imaging with a straight polycapillary X-ray collimator
- 2020
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 15:12
-
Tidskriftsartikel (refereegranskat)abstract
- Due to the availability of X-ray imaging detectors, full-field X-ray fluorescence (FF-XRF) imaging technique has become achievable, which provides an alternative to scanning X-ray fluorescence imaging with a micro-focus X-ray beamline. In this paper, we present a setup based on straight capillary optics and an energy-dispersive hybrid pixel detector, which can perform simultaneous mapping of several chemical elements. The photon transmission efficiency and spatial resolution are compared between two X-ray collimation setups: one using pinhole optics and one using straight polycapillary optics. There is a tradeoff between the spatial resolution and transmission efficiency when considering X-ray optics. When optimizing the spatial resolution, using straight capillary optics achieved a higher intensity gain when comparing with the pinhole setup. Characterization of the polycapillary imaging setup is performed through analyzing various samples in order to investigate the spatial frequency response and the energy sensitivity. This developed setup is capable of FF-XRF imaging in characteristic energies below 20 keV, while for higher energies the spatial resolution is affected by photon transmission through the collimator. This work shows the potential of the FF-XRF instrument in the monitoring of toxic metal distributions in environmental mapping measurements.
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| 3. |
- An, Siwen, et al.
(författare)
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Geometrical influence on Hg determination in wet sediment using K-shell fluorescence analysis
- 2023
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Ingår i: X-Ray Spectrometry. - : John Wiley and Sons Ltd. - 0049-8246 .- 1097-4539. ; 52:4, s. 82-196
-
Tidskriftsartikel (refereegranskat)abstract
- To quickly identify maritime sites polluted by heavy metal contaminants, reductions in the size of instrumentation have made it possible to bring an X-ray fluorescence (XRF) analyzer into the field and in direct contact with various samples. The choice of source-sample-detector geometry plays an important role in minimizing the Compton scattering noise and achieving a better signal-to-noise ratio (SNR) in XRF measurement conditions, especially for analysis of wet sediments. This paper presents the influence of geometrical factors on a prototype, designed for in situ XRF analysis of mercury (Hg) in wet sediments using a 57Co excitation source and an X-ray spectrometer. The unique XRF penetrometer prototype has been constructed and tested for maritime wet sediment. The influence on detection efficiency and SNR of various geometrical arrangements have been investigated using the combination of Monte Carlo simulations and laboratory experiments. Instrument calibration was performed for Hg analysis by means of prepared wet sediments with the XRF prototype. The presented results show that it is possible to detect Hg by K-shell emission, thus enabling XRF analysis for underwater sediments. Consequently, the XRF prototype has the potential to be applied as an environmental screening tool for analysis of polluted sediments with relatively high concentrations (e.g., >2880 ppm for Hg), which would benefit in situ monitoring of maritime pollution caused by heavy metals. © 2022 The Authors
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| 4. |
- An, Siwen
(författare)
-
Spectroscopic and Microscopic X-ray Fluorescence Analysis for Environmental and Industrial Applications
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Heavy metals are well-known environmental pollutants due to its potential impact on associated ecosystems and human health. Thus, it is important to monitor the levels of heavy metals in the environment. X-ray fluorescence (XRF) analysis is a powerful and effective screening tool in measuring the concentration of multi-elements simultaneously.This thesis provides insight into development and implementation of XRF instruments for environmental monitoring and industrial process control. The XRF method was compared with a commercial scanning electron microscope with energy dispersive spectroscopy (SEM-EDS) for fly ash samples. Qualitative analysis and semi-quantitative analysis of Na, S, Cl, K and Cd in incineration fly ash were performed with these two similar techniques. One of the challenges of using XRF is the scattering background noise from the primary beam, which decreases the detection limit and the sensitivity of the measurement system. Hence, an X-ray beam filter was chosen to suppress the background noise for a specific element, Cr, in leachate. Numerical simulations and experiments were developed to find the proper filter material and thickness by calculating the X-ray fluorescence intensities and the signal-to-noise ratio. The developed system is capable of online monitoring of Cr levels, to certify that the concentration is below the threshold level in leachate. An XRF prototype was built and calibrated for underwater Hg analysis in maritime wet sediment using a radioisotope source. The presented results show that it is possible to detect Hg by K-shell emission thus enabling XRF analysis for sediment underwater.For non-homogeneous samples, an image revealing the elemental distribution can be achieved by micro-XRF (µ-XRF). XRF mapping of element distributions on a microscopic level was obtained by using scanning XRF microscopy and full-field XRF projection microscopy (FF-XRF). The spatial resolution of the scanning XRF imaging setup using an X-ray tube is in the order of 100 µm, but need to be further improved to measure the homogeneity of S on individual fiber level in pulp and paper industry. For the scanning technique, it is a tradeoff between resolution and measurement time. Another technique is FF-XRF imaging, and a setup was implemented using an energy resolving pixel detector and X-ray optics. The capabilities and limitations of using X-ray optics in XRF imaging systems have been identified. These microscopy measurements can guide further comprehensive environmental and industrial monitoring missions, utilizing elemental distribution information.
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| 5. |
- Dreier, Till, et al.
(författare)
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A USB 3.0 readout system for Timepix3 detectors with on-board processing capabilities
- 2018
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 13
-
Tidskriftsartikel (refereegranskat)abstract
- Timepix3 is a high-speed hybrid pixel detector consisting of a 256 x 256 pixel matrix with a maximum data rate of up to 5.12 Gbps (80 MHit/s). The ASIC is equipped with eight data channels that are data driven and zero suppressed making it suitable for particle tracking and spectral imaging.In this paper, we present a USB 3.0-based programmable readout system with online preprocessing capabilities. USB 3.0 is present on all modern computers and can, under real-world conditions, achieve around 320MB/s, which allows up to 40 MHit/s of raw pixel data. With on-line processing, the proposed readout system is capable of achieving higher transfer rate (approaching Timepix4) since only relevant information rather than raw data will be transmitted. The system is based on an Opal Kelly development board with a Spartan 6 FPGA providing a USB 3.0 interface between FPGA and PC via an FX3 chip. It connects to a CERN T imepix 3 chipboard with standard VHDCI connector via a custom designed mezzanine card. The firmware is structured into blocks such as detector interface, USB interface and system control and an interface for data pre-processing. On the PC side, a Qt/C++ multi-platformsoftware library is implemented to control the readout system, providing access to detector functions and handling high-speed USB 3.0 streaming of data from the detector.We demonstrate equalisation, calibration and data acquisition using a Cadmium Telluride sensor and optimise imaging data using simultaneous ToT (Time-over-Threshold) and ToA (Timeof- Arrival) information. The presented readout system is capable of other on-line processing such as analysis and classification of nuclear particles with current or larger FPGAs.
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| 6. |
- Esebamen, Omeime X., et al.
(författare)
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High resolution, low energy electron detector
- 2011
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 6:1, s. Art. no. P01001-
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Tidskriftsartikel (refereegranskat)abstract
- Electron detection at low energy range for scanning electron microscope (SEM), electron capture detector and electron probe micro-analysis (EPMA) applications, require detectors with high sensitivity and accuracy for low energy range. Such detectors must therefore have a thin entrance window and low recombination at the Si-SiO2 interface. An electron detector with 100 photons to electron-hole pair production rate having a 10 nm SiO2 passivating layer reveals a responsivity of approximately 0.25 A/W when irradiated. Simulations results showing the responsivity of electron interaction between detectors of varied interface fixed oxide charge density Qf show that there is an appreciable difference with the responsivity of a p +n detector and that of an n+p. The simulation results also show the significance of the effect of the minority carriers transport velocity Sn,p on the responsivity of the detector. © 2011 IOP Publishing Ltd and SISSA.
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| 7. |
- Fröjdh, Christer, et al.
(författare)
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Hard X-ray imaging and particle detection with TIMEPIX3
- 2016
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9781510603271 - 9781510603288
-
Konferensbidrag (refereegranskat)abstract
- CMOS pixel electronics open up for applications with single photon or particle processing. TIMEPIX3 is a readout chip in the MEDIPIX family with the ability to simultaneously determine energy and time of interaction in the pixel. The device is fully event driven, sending out data on each interaction at a maximum speed of about 40 Mhits/s. The concept allows for off-line processing to correct for charge sharing or to find the interaction point in multi pixel events. The timing resolution of 1.56 ns allows for three dimensional tracking of charged particles in a thick sensor due to the drift time for the charge in the sensor. The experiments in this presentation have been performed with silicon sensors bonded MEDIPIX family chips with special focus on TIMEPIX3. This presentation covers basic performance of the chip, spectral imaging with hard X-rays, detection and imaging with charged particles and neutrons. Cluster identification, centroiding and charge summing is extensively used to determine energy and position of the interaction. For neutron applications a converter layer was placed on top of the sensor.
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| 8. |
- Fröjdh, Christer, et al.
(författare)
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Spectral resolution in pixel detectors with single photon processing
- 2013
-
Ingår i: Proceedings SPIE Optical Engineering + Applications, 2013. - : SPIE - International Society for Optical Engineering. - 9780819497024
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 9. |
- Fröjdh, Erik, 1984-, et al.
(författare)
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Probing Defects in a Small Pixellated CdTe Sensor Using an Inclined Mono Energetic X-Ray Micro Beam
- 2012
-
Ingår i: 2012 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE RECORD (NSS/MIC). - : IEEE conference proceedings. - 9781467320306 - 9781467320283 ; , s. 4233-4236
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- High quantum efficiency is important in X-ray imaging applications. This means using high-Z sensor materials. Unfortunately many of these materials suffer from defects that cause non-ideal charge transport. In order to increase the understanding of these defects, we have mapped the 3D response of a number of defects in two 1 mm thick CdTe sensors with different pixel sizes (55 mu m and 110 mu m) using a monoenergetic microbeam at 79 keV. The sensors were bump bonded to Timepix read out chips. Data was collected in photon counting as well as time-over-threshold mode. The time-over-threshold mode is a very powerful tool to investigate charge transport properties and fluorescence in pixellated detectors since the signal from the charge that each photon deposits in each pixel can be analyzed. Results show distorted electrical field around the defects and indications of excess leakage current and large differences in behavior between electron collection and hole collection mode. The experiments were carried out in the Extreme Conditions Beamline I15 at Diamond Light Source.
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| 10. |
- Fröjdh, Erik, et al.
(författare)
-
Probing Defects in a Small Pixellated CdTe Sensor Using an Inclined Mono Energetic X-Ray Micro Beam
- 2013
-
Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 60:4, s. 2864-2869
-
Tidskriftsartikel (refereegranskat)abstract
- High quantum efficiency is important in X-ray imaging applications. This means using high-Z sensor materials. Unfortunately many of these materials suffer from defects that cause non-ideal charge transport. In order to increase the understanding of these defects, we have mapped the 3D response of a number of defects in two 1 mm thick CdTe sensors with different pixel sizes (55 mu m and 110 mu m) using a monoenergetic microbeam at 79 keV. The sensors were bump bonded to Timepix read out chips. Data was collected in photon counting as well as time-over-thresholdmode. The time-over-thresholdmode is a very powerful tool to investigate charge transport properties and fluorescence in pixellated detectors since the signal from the charge that each photon deposits in each pixel can be analyzed. Results show distorted electrical field around the defects, indications of excess leakage current and large differences in behavior between electron collection and hole collection mode. The experiments were carried out on the Extreme Conditions Beamline I15 at Diamond Light Source.
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| 11. |
- Johannesson, Magnus, et al.
(författare)
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Genome-wide association meta-analysis of 78,308 individuals identifies new loci and genes influencing human intelligence
- 2017
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Ingår i: Nature Genetics. - : Nature Research (part of Springer Nature). - 1061-4036 .- 1546-1718.
-
Tidskriftsartikel (refereegranskat)abstract
- Intelligence is associated with important economic and health-related life outcomes. Despite intelligence having substantial heritability (0.54) and a confirmed polygenic nature, initial genetic studies were mostly underpowered. Here we report a meta-analysis for intelligence of 78,308 individuals. We identify 336 associated SNPs (METAL P −8) in 18 genomic loci, of which 15 are new. Around half of the SNPs are located inside a gene, implicating 22 genes, of which 11 are new findings. Gene-based analyses identified an additional 30 genes (MAGMA P −6), of which all but one had not been implicated previously. We show that the identified genes are predominantly expressed in brain tissue, and pathway analysis indicates the involvement of genes regulating cell development (MAGMA competitive P = 3.5 × 10−6). Despite the well-known difference in twin-based heritability2 for intelligence in childhood (0.45) and adulthood (0.80), we show substantial genetic correlation (rg = 0.89, LD score regression P = 5.4 × 10−29). These findings provide new insight into the genetic architecture of intelligence.
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| 12. |
- Krapohl, David, 1980-
(författare)
-
Comparison of energy resolution spectra of CdTe TIMEPIX detector working in photon counting and time-over-threshold mode
- 2013
-
Ingår i: IEEE Nuclear Science Symposium Conference Record. ; , s. Art. no. 6829825-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Hybrid pixel detectors like the Medipix andTIMEPIX developed by the Medipix collaboration combinedwith high-z materials are of growing interest. In particular theTIMEPIX detector can be operated in photon counting mode andtime-over-threshold mode (ToT) to obtain spectral information.Previous studies showed that 110 μm pixel sizes obtain a betterenergy resolution than 55 μm pixel sizes. Furthermore, thresholdscans obtained a better spectral resolution than operation in ToTmode. In this work the influence of noise sources in differentmeasurement approaches on the spectral response of a TIMEPIXchip bump-bonded to CdTe sensor are presented. Two 1mmthick CdTe sensors with pixel sizes of 55 μm and 110 μm,bump-bonded to a TIMEPIX readout chip, were evaluated atthe Diamond Light Source synchrotron. A finely collimated,perpendicular pencil beam with x-ray energies of 25 keV and79 keV was used to investigate single pixels. A small area of 10x10pixels was investigated in ToT-mode and compared to a thresholdscan of the same pixels on both detectors. The measurementsare compared to an analytical SPICE/Python simulation thatemulates photon counting and time-over-threshold mode.
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| 13. |
- Krapohl, David, 1980-, et al.
(författare)
-
Investigation of charge collection in a CdTe-Timepix detector
- 2013
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 8:May, s. Art. no. C05003-
-
Tidskriftsartikel (refereegranskat)abstract
- Energy calibration of CdTe detectors is usually done using known reference sources disregarding the exact amount of charge that is collected in the pixels. However, to compare detector and detector model the quantity of charge collected is needed. We characterize the charge collection in a CdTe detector comparing test pulses, measured data and an improved TCAD simulation model [1]. The 1 mm thick detector is bump-bonded to a TIMEPIX chip and operating in Time-over-Threshold (ToT) mode. The resistivity in the simulation was adjusted to match the detector properties setting a deep intrinsic donor level [2]. This way it is possible to adjust properties like trap concentration, electron/hole lifetime and mobility in the simulation characterizing the detector close to measured data cite [3].
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| 14. |
- Krapohl, David, et al.
(författare)
-
Microstimulation in The Brain : Does Microdialysis Influence the Activated Volume of Tissue?
- 2009
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Ingår i: Proceedings of the COMSOL Conference Milan 2009. - Milan : COMSOL.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Deep brain stimulation (DBS) has been established as an effective treatment for Parkinson’s disease and other movement disor- ders. The stimulation is currently administered using tetrode-macroelectrodes that target the subthalamic nucleus (STN). This often leads to side effects which bias the surrounding ar- eas, e.g. the speech centre. Targeting a spe- cific brain region can better be achieved with micro-stimulation electrodes with directed elec- trical field distribution. Experimental studies showed the effectiveness of microelectrode DBS by comparing neurotransmitter outflow before and after the stimulation. The neurotransmit- ter outflow in close proximity to the stimulation is hereby measured by means of microdialysis. To establish ideal distances and stimulation strength, the electric potential around the stim- ulation electrode and microdialysis membrane were modelled using comsol Multiphysics.
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| 15. |
- Krapohl, David, 1980-
(författare)
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Monte Carlo and Charge Transport Simulation of Pixel Detector Systems
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 16. |
- Krapohl, David, et al.
(författare)
-
Simulation and measurement of short infrared pulses on silicon position sensitive device
- 2011
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 6:C01036
-
Tidskriftsartikel (refereegranskat)abstract
- Lateral position sensitive devices (PSD) are important for triangulation, alignment and surface measurements as well as for angle measurements. Large PSDs show a delay on rising and falling edges when irradiated with near infra-red light [1]. This delay is also dependent on the spot position relative to the electrodes. It is however desirable in most applications to have a fast response. We investigated the responsiveness of a Sitek PSD in a mixed mode simulation of a two dimensional full sized detector. For simulation and measurement purposes focused light pulses with awavelength of 850 nm, duration of 1 µs and spot size of 280 µm were used. The cause for the slopes of rise and fall time is due to time constants of the device capacitance as well as the photo- generation mechanism itself [1]. To support the simulated results, we conducted measurements of rise and fall times on a physical device. Additionally, we quantified the homogeneity of the device by repositioning a spot of light from a pulsed ir-laser diode on the surface area.
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| 17. |
- Krapohl, David, et al.
(författare)
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Simulation of a silicon neutron detector coated with TiB 2 absorber
- 2012
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 7:1, s. Art. no. C01096-
-
Tidskriftsartikel (refereegranskat)abstract
- Neutron radiation cannot be directly detected in semiconductor detectors and therefore needs converter layers. Planar clean-room processing can be used in the manufacturing process of semiconductor detectors with metal layers to produce a cost-effective device. We used the Geant4 Monte-Carlo toolkit to simulate the performance of a semiconductor neutron detector. A silicon photo-diode was coated with vapour deposited titanium, aluminium thin films and a titaniumdiboride (TiB 2) neutron absorber layer. The neutron capture reaction 10B(n, alpha)7Li is taken advantage of to create charged particles that can be counted. Boron-10 has a natural abundance of about SI 19.8%. The emitted alpha particles are absorbed in the underlying silicon detector. We varied the thickness of the converter layer and ran the simulation with a thermal neutron source in order to find the best efficiency of the TiB 2 converter layer and optimize the clean room process. © 2012 IOP Publishing Ltd and SISSA.
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| 18. |
- Krapohl, David, 1980-, et al.
(författare)
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Simulation of the Spectral Response of a Pixellated X-Ray Imaging Detector in Single Photon Processing Mode
- 2010
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Ingår i: 2010 Nuclear Science Symposium and Medical Imaging Conference. - : IEEE conference proceedings.
-
Konferensbidrag (refereegranskat)abstract
- X-ray imaging with spectral resolution, “Color X-ray imaging” is a new imaging technology that is currently attracting a lot of attention. It has however been observed that the quality of spectral response is degraded as the pixel size is reduced. This is an effect of charge sharing where the signal from a photon absorbed close to the border between two pixels is shared between pixels. This effect is caused by both diffusion during the charge transport and X-ray fluorescence in heavy detector materials. In order to understand the behavior of pixellated detectors with heavy detector materials operating in single photon processing mode, we have simulated the X-ray interaction with the sensor and the transport of the charge to the readout electrode using a Monte Carlo model for the X-ray interaction and a drift diffusion model for the charge transport. By combining these models, both signal and noise properties of the detector can be simulated.
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| 19. |
- Krapohl, David, 1980-, et al.
(författare)
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Validation of Geant4 Pixel Detector Simulation Framework by Measurements with the Medipix Family Detectors
- 2016
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Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 63:3, s. 1874-1881
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Tidskriftsartikel (refereegranskat)abstract
- Monte Carlo simulations are an extensively used tool for developingand understanding radiation detector systems. In this work, we usedresults of several chips and readout modes of the Medipix detector family to validatea Geant4 based pixel detector framework, developed in our group, thatis capable of simulating particle tracking, charge transport in thesensor material and different readout schemes. We experimentally verifiedthe simulation with different detector geometries in terms of pixelpitch and size as well as sensor material and sensor thickness. Thesingle pixel mode (SPM) and charge summing mode (CSM) in Medipix3 were evaluated with fluorescenceand synchrotron radiation. The integration of the charge sensitiveamplifier functionality in the simulation framework allowed to simulatethe time-over-threshold mode of the Timepix chip.Simulation and measurement have been compared in terms of spectralresolution using threshold scans in photon counting mode (Medipix3) and time over thresholdmode (Timepix). Furthercomparisons were done using X-ray tube spectra and beta decay to covera broad energy range. Additionally, TCAD simulations are performedas a comparison to a well-established simulation method. The resultsshow good agreement between simulation and measurement.
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| 20. |
- Norlin, Börje, et al.
(författare)
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Readout cross-talk for alpha-particle measurements in a pixelated sensor system
- 2015
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Ingår i: Journal of Instrumentation. - : IOP. - 1748-0221. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- Simulations in Medici are performed to quantify crosstalk and charge sharing in a hybrid pixelated silicon detector. Crosstalk and charge sharing degrades the spatial and spectral resolution of single photon processing X-ray imaging systems. For typical medical X-ray imaging applications, the process is dominated by charge sharing between the pixels in the sensor. For heavier particles each impact generates a large amount of charge and the simulation seems to over predict the charge collection efficiency. This indicates that some type of non modelled degradation of the charge transport efficiency exists, like the plasma effect where the plasma might shield the generated charges from the electric field and hence distorts the charge transport process. Based on the simulations it can be reasoned that saturation of the amplifiers in the Timepix system might generate crosstalk that increases the charge spread measured from ion impact on the sensor.
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| 21. |
- Norlin, Börje, 1967-, et al.
(författare)
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Spectroscopic X-Ray Imaging Using a Pixelated Detector with Single Photon Processing Readout
- 2010
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Ingår i: Proceedings of 2010 IEEE NUCLEAR SCIENCE SYMPOSIUM CONFERENCE. - : IEEE conference proceedings. - 9781424491063 ; , s. 1074-1078
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Konferensbidrag (refereegranskat)abstract
- Color informatics to analyze the object content in Xray images is an emerging technology. Identification of different elements for applications such as medical contrast agent imaging is possible using energy resolving X-ray imaging sensors. In this work RGB representations of transmission images of ground elements achieved with the MEDIPIX system are exemplified.
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| 22. |
- Norlin, Börje, associate professor, 1967-, et al.
(författare)
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Visualisation of sulphur on single fibre level for pulping industry
- 2023
-
Ingår i: Journal of Instrumentation. - : Institute of Physics (IOP). - 1748-0221. ; 18:01, s. C01012-C01012
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Tidskriftsartikel (refereegranskat)abstract
- In the pulp and paper industry, about 5 Mt/y chemithermomechanical pulp (CTMP) are produced globally from softwood chips for production of carton board grades. For tailor making CTMP for this purpose, wood chips are impregnated with aqueous sodium sulphite for sulphonation of the wood lignin. When lignin is sulphonated, the defibration of wood into pulp becomes more selective, resulting in enhanced pulp properties. On a microscopic fibre scale, however, one could strongly assume that the sulphonation of the wood structure is very uneven due to its macroscale size of wood chips. If this is the case and the sulphonation could be done significantly more evenly, the CTMP process could be more efficient and produce pulp even better suited for carton boards. Therefore, the present study aimed to develop a technique based on X-ray fluorescence microscopy imaging (µXRF) for quantifying the sulphur distribution on CTMP wood fibres. Firstly, the feasibility of µXRF imaging for sulphur homogeneity measurements in wood fibres needs investigation. Therefore, clarification of which spatial and spectral resolution that allows visualization of sulphur impregnation into single wood fibres is needed. Measurements of single fibre imaging were carried out at the Argonne National Laboratory’s Advanced Photon Source (APS) synchrotron facility. With a synchrotron beam using one micrometre scanning step, images of elemental mapping are acquired from CTMP samples diluted with non-sulphonated pulp under specified conditions. Since the measurements show significant differences between sulphonated and non-sulphonated fibres, and a significant peak concentration in the shell of the sulphonated fibres, the proposed technique is found to be feasible. The required spatial resolution of the µXRF imaging for an on-site CTMP sulphur homogeneity measurement setup is about 15 µm, and the homogeneity measured along the fibre shells is suggested to be used as the CTMP sulphonation measurement parameter.
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| 23. |
- Schübel, Armin, et al.
(författare)
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A Geant4 based framework for pixel detector simulation
- 2014
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 9:12
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Tidskriftsartikel (refereegranskat)abstract
- The output from a hybrid pixel detector depends on the interaction of the radiation with the sensor material, the transport of the resulting charge in the sensor, the pulse processing in the readout circuit and processing of the resulting signal. In order to understand the full behaviour of the device and to predict the performance of future devices it is important to have a framework that can simulate the entire process in the detector system.Geant4 is a Monte Carlo based toolkit for simulation of particle interaction with matter which is developed and actively used for CERN experiments and detector development [1]. By extending the Monte Carlo code in Geant4 with a charge carrier transport model of the sensor material and basic amplifier functionality as well as read out logic, a simulation of the complete detector system is possible.The MEDIPIX is a state of the art hybrid pixel detector that allows bonding of a wide range of sensor materials [2,3]. Simulation models have been developed and tested for different chips from the MEDIPIX family. The simulation is defined using configuration files to set the geometry, sensor material properties, number of pixels, pixel pitch and chip properties. Source properties as well as filters and objects in the beam can be added for different experimental set-ups. The interaction of radiation with the sensor is taken into account in the transport of the charge carriers in the sensor material and a current induced in the pixel electrode that triggers an amplifier response. Simulation results have been verified with X-ray fluorescence and radioactive sources using MEDIPIX family chips. In this paper we present the developed simulation framework and first results.
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| 24. |
- Slavicek, Tomas, et al.
(författare)
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A thermal neutron detector based on planar silicon sensor with TiB 2 coating
- 2012
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 7:1, s. Art. no. C01053-
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Tidskriftsartikel (refereegranskat)abstract
- Neutron radiation as a non-ionizing radiation is particularly difficult to detect; therefore a conversion material is required. The conversion material converts neutrons into secondary charged particles in order for them to be detected in a silicon detector. The use of titanium diboride (TiB 2) as the conversion material deposited by an electron beam-physical vapour deposition (EB-PVD) as a part of a front-side contact of a planar silicon detector is presented. The effect of different front-side contact material compositions is discussed. The detectors behaviour was examined using alpha particles and thermal neutrons from an 241Am-Be source. Simultaneously, a Geant4 simulation was so as executed to evaluate the conversion layer functionality and to discover the conversion material thickness for the best neutron detection efficiency. © 2012 IOP Publishing Ltd and SISSA.
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| 25. |
- Thungström, Göran, et al.
(författare)
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Fabrication, characterization and simulation of channel stop for n in p-substrate silicon pixel detectors
- 2014
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 9, s. C07013-
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Tidskriftsartikel (refereegranskat)abstract
- Silicon detectors made on p-substrates are expected to have a better radiation hardness as compared to detectors made on n-substrates. However, the fixed positive oxide charges induce an inversion layer of electrons in the substrate, which connects the pixels. The common means of solving this problem is by using a p-spray, individual p-stops or a combination of the two. Here, we investigate the use of field plates to suppress the fixed positive charges and to prevent the formation of an inversion layer. The fabricated detector shows a high breakdown voltage and low interpixel leakage current for a structure using biased field plates with a width of 20 m m. By using a spice model for simulation of the preamplifier, a cross talk of about 1.6% is achieved with this detector structure. The cross talk is caused by capacitive and resistive coupling between the pixels.
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| 26. |
- Thungström, Göran, et al.
(författare)
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Measurement of the sensitive profile in a solid state silicon detector, irradiated by X-rays
- 2013
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Ingår i: Journal of Instrumentation. - : IOP. - 1748-0221. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- A newly constructed solid state silicon dose profile detector is characterized concerning its sensitive profile. The use of the MEDIPIX2 sensor system displays an excellent method to align an image of an X-ray slit to a sample under test. The scanning from front to reverse side of the detector, show a decrease in sensitivity of 20%, which indicates a minority charge carrier lifetime of 0.18 ms and a diffusion length of 460 mu m. The influence of diced edges results in a volumetric efficiency of 59%, an active volume of 1.2 mm(2) of total 2.1 mm(2).
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| 27. |
- Zeeshan, Faisal, et al.
(författare)
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Study of heavy metals including mercury within Fiber Banks of Västernorrland and Norrbotten counties by portable X-RayFluorescence (pXRF) spectrometry
- 2021
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Ingår i: Accelerating the progress towards the 2030 SDGs in times of crisis. - 9789189341173 ; , s. 265-276
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Konferensbidrag (refereegranskat)abstract
- Discharge of waste water from pulp and paper industries has led to environmental impact in the formation of sediment layers, so called fiber banks, on the coast of Västernorrland and Norrbotten counties in Sweden. These fiber banks are thick underwater deposits which are highly contaminated with some toxic metals such as Al, Cr, Fe, Cu, Zn, As, Pb, Hg. These metals can lead to several consequences for the environment, thus ultimately having harmful effects on living organisms. Our purpose is to study several of these toxic metals and analyze the concentration level by using portable X-ray Fluorescence (pXRF) spectrometry for rapid sample characterization of wet samples. Field analyses are highly affected by moisture and it is difficult to obtain measurement accuracy. Therefore, moisture tests were performed by air drying samples at room temperature from 0 to 24 h. Some of the samples were oven dried for 48 h at 950 C, dried, grinded and turned into pellets and performed laboratory measurements to compare results with field measurements. Our aim is to provide an improved state of facts for decision makers to prevent and reduce marine pollution and to protect and restore ecosystems in order to avoid significant adverse impacts, and take actions for their restoration in order to achieve healthy and productive oceans. A future outcome is to reach the sustainable development goal (SDG) stated by the UN at target 14.1 and 14.2 “Life below water”.
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| 28. |
- Zeeshan, Faisal, et al.
(författare)
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Synchrotron measurements of Sulphonation degree from Chemimechanical pulp (CTMP) to optimize the pulping process for packaging products
- 2022
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The manufacturing of CTMP has a significant role in producing sustainable packaging products. But the strategy to improve the impregnation technology is still challenging due to the uneven distribution of Na2SO3. Our aim was to investigate the oxidation states of Sulphonate present in our handmade paper samples which consist of different CTMP percentages. Therefore, XANES measurements were done to investigate the oxidation states and XRF measurements were done to see the presence of other elements. XRF mapping was also done to know the distribution of Na in the samples.
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