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  • 1.
    Croci, Gabriele
    et al.
    Univ Milano Bicocca, Milan, Italy.
    Muraro, Andrea
    CNR, Milan, Italy.
    Cippo, Enrico Perelli
    CNR, Milan, Italy.
    Grosso, Giovanni
    CNR, Milan, Italy.
    Hoglund, Carina
    European Spallat Source ESS AB, Lund.
    Hall-Wilton, Richard
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion. European Spallat Source ESS AB, Lund.
    Murtas, Fabrizio
    Ist Nazl Fis Nucl, Frascati, Italy.
    Raspino, Davide
    Rutherford Appleton Lab, Didcot, Oxon, England.
    Robinson, Linda
    European Spallat Source ESS AB, Lund.
    Rhodes, Nigel
    Rutherford Appleton Lab, Didcot, Oxon, England.
    Rebai, Marica
    CNR, Milan, Italy.
    Schooneveld, Erik
    Rutherford Appleton Lab, Didcot, Oxon, England.
    Defendi, Ilario
    TUM, Garching, Germany.
    Zeitelhack, Karl
    TUM, Garching, Germany.
    Tardocchi, Marco
    CNR, Milan, Italy.
    Gorini, Giuseppe
    Univ Milano Bicocca, Milan, Italy.
    I-BAND-GEM: a new way for improving BAND-GEM efficiency to thermal and cold neutrons2019Ingår i: The European Physical Journal Plus, ISSN 2190-5444, E-ISSN 2190-5444, Vol. 134, nr 4, artikel-id 166Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    .The BAND-GEM detector represents one of the novel thermal neutron detection devices that have been developed in order to fulfil the needs of high intensity neutron sources that, like ESS (the European Spallation Source), will start operation in the next few years. The first version of this detector featured a detection efficiency of about 40% for neutrons with a wavelength of 4 angstrom, a spatial resolution of about 6mm and a rate capability in the order of some MHz/cm(2). The novelty of this device is represented by an improved 3D converter cathode (10 cm thick) based on (B4C)-B-10-coated aluminum grids positioned in a controlled gas mixture volume put on top of a Triple GEM amplifying stage. The position where the neutron interacts in the converter depends on their energy and it was observed that the first version of the detector would suffer from an efficiency decrease for long (>5 angstrom) neutron wavelength. This paper describes how the new 3D cathode allowed improving the detection efficiency at long neutron wavelengths while keeping all the benefits of the first BAND-GEM version.

  • 2.
    Dreier, Till
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Krapohl, David
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Maneuski, Dzimitry
    School of Physics & Astronomy, University of Glasgow, Glasgow, Scotland.
    Lawal, Najeem
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Schöwerling, Jan Oliver
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion. Osnabrück University of Applied Sciences, Osnabrück, Germany.
    O'Shea, Val
    School of Physics & Astronomy, University of Glasgow, Glasgow, Scotland.
    Fröjdh, Christer
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    A USB 3.0 readout system for Timepix3 detectors with on-board processing capabilities2018Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 13, artikel-id C11017Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 3.
    Fröjdh, Christer
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Krapohl, David
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Reza, Salim
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Fröjdh, Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Norlin, Börje
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Spectral resolution in pixel detectors with single photon processing2013Ingår i: Proceedings of SPIE - The International Society for Optical Engineering, SPIE - International Society for Optical Engineering, 2013, s. Art. no. 88520O-Konferensbidrag (Övrigt vetenskapligt)
    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.

  • 4.
    Fröjdh, Erik
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Fröjdh, Christer
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Norlin, Börje
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Mapping the x-ray response of a CdTe sensor with small pixels using an x-ray microbeam and a single photon processing readout chip2011Ingår i: Proceedings of SPIE - The International Society for Optical Engineering / [ed] Larry A. Franks, Ralph B. James, Arnold Burger, SPIE - International Society for Optical Engineering, 2011, s. Art. no. 814208-Konferensbidrag (Refereegranskat)
    Abstract [en]

    CdTe is a promising material for X-ray imaging since it has high stopping power for X-rays. However defects in the material, non ideal charge transport and long range X-ray fluorescence deteriorates the image quality. We have investigated the response of a CdTe sensor with very small pixels using an X-ray microbeam entering the sensor at a small incident angle. Effects of defects as well as depth of interaction can be measured by this method. Both electron and hole collection mode has been tested. The results show distorted electrical field around defects in the material and also shows the small pixel effect. It is also shown that charge summing can be used to get correct spectral information.

  • 5.
    Krapohl, David
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Comparison of energy resolution spectra of CdTe TIMEPIX detector working in photon counting and time-over-threshold mode2013Ingår i: IEEE Nuclear Science Symposium Conference Record, 2013, s. Art. no. 6829825-Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 6.
    Krapohl, David
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Monte Carlo and Charge Transport Simulation of Pixel Detector Systems2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

  • 7.
    Krapohl, David
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Schubel, Armin
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion. University of Heidelberg, Heidelberg, Germany.
    Fröjdh, Erik
    Paul Scherrer Institute, Villigen, Switzerland.
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Fröjdh, Christer
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion. Paul Scherrer Institute, Villigen, Switzerland.
    Validation of Geant4 Pixel Detector Simulation Framework by Measurements with the Medipix Family Detectors2016Ingår i: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 63, nr 3, s. 1874-1881, artikel-id 7497723Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 8.
    Reza, Salim
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Wong, Winnie
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Fröjdh, Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Norlin, Börje
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Fröjdh, Christer
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Thungstörm, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Thim, Jan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Smart dosimetry by pattern recognition using a single photon counting detector system in time over threshold mode2012Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 7, nr 1, s. Art. no. C01027-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The function of a dosimeter is to determine the absorbed dose of radiation, for those cases in which, generally, the particular type of radiation is already known. Lately, a number of applications have emerged in which all kinds of radiation are absorbed and are sorted by pattern recognition, such as the Medipix2 application in [1]. This form of smart dosimetry enables measurements where not only the total dosage is measured, but also the contributions of different types of radiation impacting upon the detector surface. Furthermore, the use of a photon counting system, where the energy deposition can be measured in each individual pixel, ensures measurements with a high degree of accuracy in relation to the pattern recognition. In this article a Timepix [2] detector system has been used in the creation of a smart dosimeter for Alpha, Beta and Gamma radiation. When a radioactive particle hits the detector surface it generates charge clusters and those impacting upon the detector surface are read out and image processing algorithms are then used to classify each charge cluster. The individual clusters are calculated and as a result, the dosage for each type of radiation is given. In some cases, several particles can impact in roughly the same place, forming overlapping clusters. In order to handle this problem, a cluster separation method has been added to the pattern recognition algorithm. When the clusters have been separated, they are classified by shape and sorted into the correct type of radiation. The algorithms and methods used in this dosimeter have been developed so as to be simple and computationally effective, in order to enable implementation on a portable device. © 2012 IOP Publishing Ltd and SISSA.

  • 9.
    Schübel, Armin
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion. University of Heidelberg, Heidelberg, Germany.
    Krapohl, David
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Fröjdh, Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion. CERN, Genève 23, Switzerland.
    Fröjdh, Christer
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    A Geant4 based framework for pixel detector simulation2014Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 9, nr 12, artikel-id C12018Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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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