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  • 1.
    Ballabriga, Rafael
    et al.
    Cern.
    Alozy, Jerome
    Cern.
    Campbell, Michael
    Cern.
    Fiederle, Michael
    FMF Frieburg.
    Fröjdh, Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Heijne, E H M
    Cern.
    Blaj, Gabriel
    Slac.
    Llopart, Xavier
    Cern.
    Pichotka, M
    Procz, Simon
    FMF Frieburg.
    Tlustos, Lukas
    Cern.
    Wong, Winnie
    Cern.
    The Medipix3RX: a high resolution, zero dead-time pixel detector readout chip allowing spectroscopic imaging2013Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 8, nr 2, s. C02016-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Medipix3 chips have been designed to permit spectroscopic imaging in highly segmented hybrid pixel detectors. Spectral degradation due to charge sharing in the sensor has been addressed by means of an architecture in which adjacent pixels communicate in the analog and digital domains on an event-by-event basis to reconstruct the deposited charge in a neighbourhood prior to the assignation of the hit to a single pixel. The Medipix3RX chip architecture is presented. The first results for the characterization of the chip with 300 μm thick Si sensors are given. ~ 72e− r.m.s. noise and ~ 40e− r.m.s. of threshold dispersion after chip equalization have been measured in Single Pixel Mode of operation. The homogeneity of the image in Charge Summing mode is comparable to the Single Pixel Mode image. This demonstrates both modes are suitable for X-ray imaging applications.

  • 2.
    Campbell, M.
    et al.
    CERN, CH-1211 Geneva 23, Switzerland.
    Alozy, J.
    CERN, CH-1211 Geneva 23, Switzerland.
    Ballabriga, R.
    CERN, CH-1211 Geneva 23, Switzerland.
    Fröjdh, Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion. CERN, CH-1211 Geneva 23, Switzerland.
    Heijne, E.
    CERN, CH-1211 Geneva 23, Switzerland.
    Llopart, X.
    CERN, CH-1211 Geneva 23, Switzerland.
    Poikela, T.
    CERN, CH-1211 Geneva 23, Switzerland.
    Tlustos, L.
    CERN, CH-1211 Geneva 23, Switzerland.
    Valerio, P.
    CERN, CH-1211 Geneva 23, Switzerland.
    Wong, W.
    CERN, CH-1211 Geneva 23, Switzerland.
    Towards a new generation of pixel detector readout chips2016Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 11, nr 1, artikel-id C01007Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Medipix3 Collaboration has broken new ground in spectroscopic X-ray imaging and in single particle detection and tracking. This paper will review briefly the performance and limitations of the present generation of pixel detector readout chips developed by the Collaboration. Through Silicon Via technology has the potential to provide a significant improvement in the tile-ability and more flexibility in the choice of readout architecture. This has been explored in the context of 3 projects with CEA-LETI using Medipix3 and Timepix3 wafers. The next generation of chips will aim to provide improved spectroscopic imaging performance at rates compatible with human CT. It will also aim to provide full spectroscopic images with unprecedented energy and spatial resolution. Some of the opportunities and challenges posed by moving to a more dense CMOS process will be discussed.

  • 3.
    De Gaspari, Massimiliano
    et al.
    CERN, Geneva, Switzerland.
    Alozy, Jerome
    CERN, Geneva, Switzerland.
    Ballabriga, Rafael
    CERN, Geneva, Switzerland.
    Campbell, Michael
    CERN, Geneva, Switzerland.
    Fröjdh, Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion. CERN, Geneva, Switzerland.
    Idarraga, John
    CERN, Geneva, Switzerland.
    Kulis, S
    CERN, Geneva, Switzerland.
    Llopart, Xavier
    CERN, Geneva, Switzerland.
    Poikela, Toumas
    CERN, Geneva, Switzerland.
    Valerio, P
    CERN, Geneva, Switzerland.
    Wong, Winnie
    CERN, Geneva, Switzerland.
    Design of the analog front-end for the Timepix3 and Smallpix hybrid pixel detectors in 130 nm CMOS technology2014Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 9, s. Art. no. C01037-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes a front-end for hybrid pixel readout chips, which was developed for the Timepix3 and Smallpix ASICs. The front-end contains a single-ended preamplifier with a structure for leakage current compensation which can handle both signal polarities, and a single-threshold discriminator with compensation for pixel-to-pixel mismatch. Preamplifier and discriminator are required to be fast, to allow a Time-Of-Arrival (TOA) measurement with a resolution of 1.56 ns. Time-Over-Threshold (TOT) is also measured; the monotonicity of TOT with respect to the input charge is greatly improved as compared to the previous Timepix chip. The analog area is only 55 μm × 13.5 μm. Timepix3 has already been fabricated and the first test results are also presented in this paper.

  • 4.
    Fröjdh, Anna
    et al.
    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.
    Thungström, Göran
    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.
    Processing and characterization of a MEDIPIX2-compatible silicon sensor with 220 mu m pixel size2011Ingår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 633, nr Suppl 1, s. S78-S80Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pixellated silicon detectors with a pixel size of 220 um have been fabricated at Mid Sweden University. The detectors will be bonded to the MEDIPIX2 [1] readout chip. The purpose is to investigate the performance of an energy sensitive X-ray imaging sensor with reduced charge sharing.

    The detectors were fabricated on high purity silicon with a wafer thickness of 500 um and a resistivity of more than 15 kohmcm. One reason for the choice of material was to get experience for future work with very thick detectors requiring ultra high resistivity in order to be depleted. During the initial work in this project some issued were found concerning inter pixel resistance and the efficiency of the guard rings. This led to a study of existing papers on the subject [2,3,4,5] and to extensive simulations of the electric field and the charge transport in different parts of the device.

    A modified process has been developed using alternating p+ and n+ guard rings and an outer n+ doping. The results of the simulations and the process will be described as well as an outline for a process for fabrication of very thick detectors with limited guard ring extension.

    References[1] - X. Llopart, M. Campbell, R. Dinapoli, D. San Segundo and E. Pernigotti, IEEE Trans. Nucl. Sci., vol. 49, 2279-2283, October 2002.[2] – L. Evensen, A. Hanneborg, B Sundby Avset, M. Mese, Nuclear Instruments and Methods in Physics Research A 337 (1993) 44 – 52[3] – T. Pavalainen, T. Tuuva, K. Leinonen, Nuclear Instruments and Methods in Physics Research A 573 (2007) 277 – 279[4] – Z. Li, W. Huang, L. J. Zhao, IEEE Trans. Nucl. Sci., vol. 47, No. 3. 729 – 735 , June 2000.[5] – D. Han, C. Wang, G. Wang, S. Du, L. Shen, X. Tian, X. Zhang, IEEE Transactions on Electron devices, Vol. 50, No. 2, 537 – 540, February 2003

  • 5.
    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.

  • 6.
    Fröjdh, Christer
    et al.
    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.
    Jakubek, Jan
    Czech Technical University, Prague, Czech Republic.
    Holy, Tomas
    Czech Technical University, Prague, Czech Republic.
    Fröjdh, Anna
    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.
    Characterization of area sensitivity in 55 um pixellated CdTe X-ray imaging detectors2007Ingår i: IEEE Nuclear Science Symposium Conference Record, New York: IEEE conference proceedings, 2007, s. 1234-1236Konferensbidrag (Refereegranskat)
    Abstract [en]

    X-ray imaging detectors with energy resolution, based on a single photon processing CMOS readout circuit attached to a detector chip, are being developed by different groups. In order to achieve high quantum efficiency it is preferable to use high-Z semiconductor materials. However the fluorescent X-ray photons of such materials have high energies and are able to travel long distances thereby reducing both the spatial resolution and the energy resolution of the detector. In addition charge sharing in the detector and non-uniformities in both the detector and the readout electronics will affect the signal. In this work we have characterized a 1 mm thick CdTe detector with a pixel size of 55 um x 55 um, bump bonded to the MEDIPIX2 single photon processing readout chip. The area sensitivity of the detector is evaluated using a narrow X-ray beam of monoenergetic photons. From these measurements the effects of fluorescence and charge sharing can be evaluated.

  • 7.
    Fröjdh, Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Hybrid pixel detectors: Characterization and optimization2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 8.
    Fröjdh, Erik
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion. CERN, Route de Meyrin 385, Geneva, Switzerland .
    Ballabriga, R.
    CERN, Route de Meyrin 385, Geneva, Switzerland .
    Campbell, M.
    CERN, Route de Meyrin 385, Geneva, Switzerland .
    Fiederle, M.
    Institute of Photon Science and Synchrotrom Radiation, ANKA Synchrotron Radiation Facility Karlsruhe, Institute of Technology KIT, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany .
    Hamann, E.
    Institute of Photon Science and Synchrotrom Radiation, ANKA Synchrotron Radiation Facility Karlsruhe, Institute of Technology KIT, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany .
    Koenig, T.
    Institute of Photon Science and Synchrotrom Radiation, ANKA Synchrotron Radiation Facility Karlsruhe, Institute of Technology KIT, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany .
    Llopart, X.
    Institute of Photon Science and Synchrotrom Radiation, ANKA Synchrotron Radiation Facility Karlsruhe, Institute of Technology KIT, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany .
    Magalhaes, D. D. P.
    Brazilian Synchrotron Light Laboratory LNLS, Caixa Postal 6192, CEP 13083-970, Campinas - SP, Brazil .
    Zuber, M.
    Institute of Photon Science and Synchrotrom Radiation, ANKA Synchrotron Radiation Facility Karlsruhe, Institute of Technology KIT, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany .
    Count rate linearity and spectral response of the Medipix3RX chip coupled to a 300μm silicon sensor under high flux conditions2014Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 9, nr 4, s. Art. no. C04028-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For clinical X-ray imaging, the detector performance under high flux conditions is very important, with typical flux rates for modern CT systems reaching 109 photons s-1 mm-2 in the direct beam. In addition, for spectral imaging a good energy resolution under these conditions is needed. This poses difficulties, since pulse pileup in the pixel electronics does not only affect the count rate, leading to a deviation from the otherwise linear behavior, but also degrades the spectral response of the detector, making k-edge subtraction and other contrast enhancement techniques less efficient. In this paper, we investigate the count rate capabilities and the energy response of the Medipix3RX chip under high flux conditions using 10 keV monochromatic photons. © CERN 2014.

  • 9.
    Fröjdh, Erik
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion. CERN, Geneva, Switzerland.
    Bisello, F.
    IBA Dosimetty GmbH, Schwarzenhatck, Germany.;FAU Univ Erlangen Nrnberg, Erlangen, Germany..
    Campbell, M.
    CERN, Geneva, Switzerland..
    Damet, J.
    CERN, Geneva, Switzerland.;Univ Lausanne Hosp, Inst Radiat Phys, Lausanne, Switzerland..
    Hamann, E.
    KIT, ANKA Synchrotron Radiat Facil, Karlsruhe, Germany..
    Koenig, T.
    KIT, ANKA Synchrotron Radiat Facil, Karlsruhe, Germany..
    Wong, Winnie S.
    CERN, Geneva, Switzerland.;Univ Lausanne Hosp, Inst Radiat Phys, Lausanne, Switzerland..
    Zuber, M.
    KIT, ANKA Synchrotron Radiat Facil, Karlsruhe, Germany..
    Spectral response of the energy-binning Dosepix ASIC coupled to a 300 mu m silicon sensor under high fluxes of synchrotron radiation2015Ingår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 804, s. 43-49Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Dosepix hybrid pixel detector was designed for dosimetry and radiation monitoring applications. It has three programmable modes of operation: photon counting mode, energy integration mode, and dosimetry mode. The dosimetry mode measures the energy of individual X-ray photons and automatically sorts events into pre-defined energy bins. The output is a histogram representing the measured X-ray energy spectrum, permitting a dose reconstruction that accounts for the attenuation of photons at each energy bin. This presents a potential radiation protection and dosimetry instrument in medical radiodiagnostic practices, including high flux systems such as computed tomography (CT). In this paper, we characterise the Dosepix chip by investigating the energy response and count rate capabilities when coupled to a 300 pm silicon sensor under high fluxes of monochromatic synchrotron radiation. Under nominal settings, the Dosepix detector can detect photons down to 3.5 keV, with an energy resolution of 16.5% FWHM for 8.5 keV photons and 8% FWHM for 40 keV photons. The chip can count up to 1.67 Mcps/mm(2) of 40 keV photons whilst maintaining linear counting behaviour. This count rate range can be further increased by changing the programmable operating settings of the detector, making it suitable for a range of photon dosimetry applications.

  • 10.
    Fröjdh, Erik
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion. CERN, CH-1211 Geneva 23, Switzerland..
    Campbell, M.
    CERN, CH-1211 Geneva 23, Switzerland..
    De Gaspari, M.
    CERN, CH-1211 Geneva 23, Switzerland..
    Kulis, S.
    CERN, CH-1211 Geneva 23, Switzerland..
    Llopart, X.
    CERN, CH-1211 Geneva 23, Switzerland..
    Poikela, T.
    Turku Cerntre Comp Sci, Turku 20520, Finland.
    Tlustos, L.
    CERN, CH-1211 Geneva 23, Switzerland.;Univ Freiburg, D-79098 Freiburg, Germany..
    Timepix3: first measurements and characterization of a hybrid-pixel detector working in event driven mode2015Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 10, artikel-id C01039Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Timepix3 is a hybrid pixel detector readout chip. It features a data driven readout mode where the chip sends out a data packet containing pixel coordinate, time over threshold and time of arrival immediately after the hit is processed by the pixel. The maximum hit rate is 40 Mhits/cm(2)/s with a minimum time step in the arrival time measurement of 1.56 ns. The pixel matrix consist of 256 x 256 square pixels at a 55 m m pitch and the pixel front end noise is 61 e(-) RMS. In this paper we present the first radiation measurements with Timepix3 bump bonded to a 300 m m thick silicon sensor. The chip is calibrated per pixel, using internal test pulses and the calibration is verified using X-ray fluorescence. The energy resolution, threshold dispersion and gain dispersion is measured. The energy resolution in time over threshold mode under normal operation conditions is 4.07 keV FWHM at 59.5 keV. At 10.5 keV an energy resolution of 0.72 keV FWHM was achieved in photon counting mode and in time over threshold mode, by optimizing the energy response, we achieved a 1.38 keV FWHM. We also investigate the time walk and present first results on using the time information for track reconstruction.

  • 11.
    Fröjdh, Erik
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Fröjdh, Anna
    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.
    Spectral response of a silicon detector with 220 mu m pixel size bonded to MEDIPIX22011Ingår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 633, nr Supplement 1, s. S125-S127Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The standard detector used with the MEDIPIX2 [1] readout chip suffers from severe charge sharing that reduces the spectral performance of the device. This problem is expected to be solved in the MEDIPIX3 [2] design. In order to significantly reduce the charge sharing and to make a detector which could be expected to have a similar response to MEDIPIX3 we have fabricated detectors with a pixel size of 220 um and bonded these detectors to the MEDIPIX2 chip using only a limited number of pixels on the readout chip. This makes the active area of the pixel comparable with the area covered by the charge summing in MEDIPIX3.

    The charge collection properties of the device have been tested by scanning a narrow beam over a pixel. The spectral response has been measured by taking a flood exposure at different tube voltages and comparing the result with the spectrum obtained from exposing the centre of the pixel with a narrow beam thus eliminating the charge sharing. This work represents an improved characterisation as compared to [3].

    Some initial images of different objects have been taken by placing the device in an X-ray microscope with a nanofocus X-ray tube imaging objects with magnification to simulate the original pixel size of 55 um.

    References[1] - X. Llopart, M. Campbell, R. Dinapoli, D. San Segundo and E. Pernigotti, IEEE Trans. Nucl. Sci., vol. 49, 2279-2283, October 2002.[2] - R. Ballabriga, M. Campbell, E. H. M. Heijne, X. Llopart, L. Tlustos, IEEE Trans. Nucl. Sci., Vol. 54, No. 5, October 2007.[3] – B. Norlin, C. Fröjdh, G. Thungström, D. Greiffenberg, NSS Conference record,19-25 Oct. 2008, Pages:3464 – 3469, Digital Object Identifier 10.1109/NSSMIC.2008.4775083

  • 12.
    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.
    Gimenez, E
    Diamond Light Source, Didcot, Oxfordshire OX11 0DE, United Kingdom.
    Maneuski, D
    University of Glasgow, Glasgow G12 8QQ, United Kingdom.
    Marchal, J
    Diamond Light Source, Didcot, Oxfordshire OX11 0DE, United Kingdom.
    Norlin, Börje
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    O'Shea, V
    University of Glasgow, Glasgow G12 8QQ, United Kingdom.
    Stewart, G
    University of Glasgow, Glasgow G12 8QQ, United Kingdom.
    Wilhelm, H
    Diamond Light Source, Didcot, Oxfordshire OX11 0DE, United Kingdom.
    Modh Zain, R
    University of Glasgow, Glasgow G12 8QQ, United Kingdom.
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Depth of interaction and bias voltage dependence of the spectral response in a pixellated CdTe detector operating in time-over-threshold mode subjected to monochromatic X-rays2012Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 7, nr 3, s. Art. no. C03002-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High stopping power is one of the most important figures of merit for X-ray detectors. CdTe is a promising material but suffers from: material defects, non-ideal charge transport and long range X-ray fluorescence. Those factors reduce the image quality and deteriorate spectral information. In this project we used a monochromatic pencil beam collimated through a 20Όm pinhole to measure the detector spectral response in dependance on the depth of interaction. The sensor was a 1mm thick CdTe detector with a pixel pitch of 110Όm, bump bonded to a Timepix readout chip operating in Time-Over-Threshold mode. The measurements were carried out at the Extreme Conditions beamline I15 of the Diamond Light Source. The beam was entering the sensor at an angle of ∌20 degrees to the surface and then passed through ∌25 pixels before leaving through the bottom of the sensor. The photon energy was tuned to 77keV giving a variation in the beam intensity of about three orders of magnitude along the beam path. Spectra in Time-over-Threshold (ToT) mode were recorded showing each individual interaction. The bias voltage was varied between -30V and -300V to investigate how the electric field affected the spectral information. For this setup it is worth noticing the large impact of fluorescence. At -300V the photo peak and escape peak are of similar height. For high bias voltages the spectra remains clear throughout the whole depth but for lower voltages as -50V, only the bottom part of the sensor carries spectral information. This is an effect of the low hole mobility and the longer range the electrons have to travel in a low field. © 2012 IOP Publishing Ltd and Sissa Medialab srl.

  • 13.
    Fröjdh, Erik
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion. CERN, CH-1211, Geneva, 23, Switzerland .
    Fröjdh, Christer
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Gimenez, E. N.
    Diamond Light Source, Harwell Science and Innovation Campus, Chiltern, Didcot, Oxfordshire, OX11 0QX, United Kingdom .
    Krapohl, David
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Maneuski, D.
    University of Glasgow, Glasgow, G12 8QQ, United Kingdom .
    Norlin, Börje
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    O'Shea, V.
    University of Glasgow, Glasgow, G12 8QQ, United Kingdom .
    Wilhelm, H.
    Diamond Light Source, Harwell Science and Innovation Campus, Chiltern, Didcot, Oxfordshire, OX11 0QX, United Kingdom .
    Tartoni, N.
    Diamond Light Source, Harwell Science and Innovation Campus, Chiltern, Didcot, Oxfordshire, OX11 0QX, United Kingdom .
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Zain, R. M.
    University of Glasgow, Glasgow, G12 8QQ, United Kingdom .
    Probing Defects in a Small Pixellated CdTe Sensor Using an Inclined Mono Energetic X-Ray Micro Beam2013Ingår i: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 60, nr 4, s. 2864-2869Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 14.
    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.
    Gimenez, Eva
    Diamond Light Source.
    Krapohl, David
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Maneuski, Dizmitry
    Glasgow University.
    O'Shea, Val
    Glasgow University.
    Norlin, Börje
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Wilhelm, Heribert
    Diamond Light Source.
    Tartoni, Nicola
    Diamond Light Source.
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Zain, Rasif
    Glasgow University.
    Probing Defects in a Small Pixellated CdTe Sensor Using an Inclined Mono Energetic X-Ray Micro Beam2012Ingår i: 2012 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE RECORD (NSS/MIC), IEEE conference proceedings, 2012, s. 4233-4236, artikel-id 6551965Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 15.
    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.

  • 16.
    Fröjdh, Erik
    et al.
    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.
    Fröjdh, Christer
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Spectral Response in a Pixellated X-ray Imaging CdTe Detector with Single Photon Processing Readout2010Ingår i: Proceeddings of 2010 Nuclear Science Symposium and Medical Imaging Conference, IEEE conference proceedings, 2010, s. 1079-1080Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The image forming process in a CdTe detector is both a function of the X-ray interaction in the material, including scattering and fluorescence, and the charge transport in the material [2]-[4]. The response of individual photons has been investigated using two pixellated CdTe image detectors with pixel pitches of 55 mu m and 110 mu m. The detectors were bonded to TIMEPIX [5] readout chips and operated in time over threshold mode (ToT). We have illuminated the sensors with monoengertic photons generated by X-ray fluorescence in metal sheets and with gamma photons from Am-241 and Cs-137. Results shows a large degradation in energy resolution caused by charge sharing and fluorescence. By summing pixels together we can correct for the charge sharing and some, but not all fluorescence.

  • 17.
    Fröjdh, Erik
    et al.
    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.
    Fröjdh, Christer
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    X-ray absorption and charge transport in a pixellated CdTe detector with single photon processing readout2011Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 6, nr 2, s. Art. no. P02012-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The image forming process in a CdTe detector is both a function of the X-ray interaction in the material, including scattering and fluorescence, and the charge transport in the material [2-4]. The response to individual photons has been investigated using a CdTe detector with a pixel size of 110 m m, bonded to a TIMEPIX [5] readout chip operating in time over threshold mode. The device has been illuminated with mono-energetic photons generated by fluorescence in different metals and by gamma emission from Am-241 and Cs-137. Each interaction will result in charge distributed in a cluster of pixels where the total charge in the cluster should sum up to the initial photon energy. By looking at the individual clusters the response from shared photons as well as fluorescence photons can be identified and separated. By using energies below and above the K-edges of Cd and Te the contribution from fluorescence can be further isolated. The response is analyzed to investigate the effects of both charge diffusion and fluorescence on the spectral response in the detector.

  • 18.
    George, S. P.
    et al.
    CERN, CH-1211 Geneva 23, Switzerland.
    Severino, C. T.
    CERN, CH-1211 Geneva 23, Switzerland.
    Fröjdh, Erik
    CERN, CH-1211 Geneva 23, Switzerland.
    Murtas, F.
    CERN, CH-1211 Geneva 23, Switzerland.
    Silari, M.
    CERN, CH-1211 Geneva 23, Switzerland.
    Measurement of an accelerator based mixed field with a Timepix detector2015Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 10, artikel-id P03005Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present an analysis of a high energy mixed field taken with a Timepix chip at the CERF facility at CERN. The Timepix is an active array of 65K energy measuring pixels which allows visualization and energy measurement of the tracks created by individual particles. This allows characteristics of interest such as the LET and angular distributions of the incoming tracks to be calculated, as well as broad morphological track categories based on pattern recognition techniques. We compute and compare LET-like and angular information for different morphological track categories. Morphological track categories are found to possess overlapping LET and energy spectra, however the approaches are found to be complementary with morphological clustering yielding information which is indistinguishable on the basis of LET alone. The use of the Timepix as an indirect monitoring device outside of the primary beam at CERF is briefly discussed.

  • 19.
    Krapohl, David
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Fröjdh, Christer
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Fröjdh, Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Maneuski, D
    Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom .
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Investigation of charge collection in a CdTe-Timepix detector2013Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 8, nr May, s. Art. no. C05003-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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].

  • 20.
    Krapohl, David
    et al.
    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, Erik
    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.
    Fröjdh, Christer
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Simulation of the Spectral Response of a Pixellated X-Ray Imaging Detector in Single Photon Processing Mode2010Ingår i: 2010 Nuclear Science Symposium and Medical Imaging Conference, IEEE conference proceedings, 2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 21.
    Maneuski, D.
    et al.
    School of Physics and Astronomy, University of Glasgow, G12 8QQ, United Kingdom.
    Astromskas, V
    School of Physics and Astronomy, University of Glasgow, G12 8QQ, United Kingdom.
    Fröjdh, Erik
    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.
    Gimenez, E
    Diamond Light Source Ltd., Oxfordshire, Didcot OX11 0DE, United Kingdom.
    Marchal, J
    Diamond Light Source Ltd., Oxfordshire, Didcot OX11 0DE, United Kingdom.
    O'Shea, V
    School of Physics and Astronomy, University of Glasgow, G12 8QQ, United Kingdom.
    Stewart, G.
    School of Physics and Astronomy, University of Glasgow, G12 8QQ, United Kingdom.
    Tartoni, N
    Diamond Light Source Ltd., Oxfordshire, Didcot OX11 0DE, United Kingdom.
    Wilhelm, H.
    Diamond Light Source Ltd., Oxfordshire, Didcot OX11 0DE, United Kingdom.
    Wraight, K
    School of Physics and Astronomy, University of Glasgow, G12 8QQ, United Kingdom.
    Zain, R
    School of Physics and Astronomy, University of Glasgow, G12 8QQ, United Kingdom.
    Imaging and spectroscopic performance studies of pixellated CdTe Timepix detector2012Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 7, nr 1, s. Art. no. C01038-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work the results on imaging and spectroscopic performances of 14 × 14 × 1 mm CdTe detectors with 55 × 55Όm and 110 × 110Όm pixel pitch bump-bonded to a Timepix chip are presented. The performance of the 110 × 110Όm pixel detector was evaluated at the extreme conditions beam line I15 of the Diamond Light Source. The energy of X-rays was set between 25 and 77 keV. The beam was collimated through the edge slits to 20Όm FWHM incident in the middle of the pixel. The detector was operated in the time-over-threshold mode, allowing direct energy measurement. Energy in the neighbouring pixels was summed for spectra reconstruction. Energy resolution at 77 keV was found to be ΔE/E = 3.9%. Comparative imaging and energy resolution studies were carried out between two pixel size detectors with a fluorescence target X-ray tube and radioactive sources. The 110 × 110Όm pixel detector exhibited systematically better energy resolution in comparison to 55 × 55Όm. An imaging performance of 55 × 55Όm pixellated CdTe detector was assessed using the Modulation Transfer Function (MTF) technique and compared to the larger pixel. A considerable degradation in MTF was observed for bias voltages below -300 V. Significant room for improvement of the detector performance was identified both for imaging and spectroscopy and is discussed. © 2012 IOP Publishing Ltd and SISSA.

  • 22.
    Norlin, Börje
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Fröjdh, Christer
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Fröjdh, Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Spectral X-ray imaging with single photon processing detectors2013Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 8, s. Art. no. C02010-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spectral X-ray imaging with single photon processing detectors gains substantial interest for many applications. In this paper we discuss fundamental parameters as contrast to noise ratio (CNR) and spectral response as a function of the material in the object. Image properties have been simulated for different photon energies using MCNP5, assuming an ideal detector with 32 x 32 pixels. Simulations are supported by experimental results obtained with detectors from the MEDIPIX family. The CNR is strongly dependent on the number of incident photons and the number of photons absorbed in the object. The requirement for substantial absorption in the object limits the range of useful photon energies. In most cases the CNR is improved when high energy photons are removed from the spectrum. Materials can be uniquely identified or layers of different materials can be separated provided that there is a substantial difference in their spectral X-ray absorption. In most cases an absorption edge in the spectrum is needed to obtain good results. Several examples of material identification and material separation are discussed.

  • 23.
    Norlin, Börje
    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.
    O'Nils, Mattias
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Fröjdh, Anna
    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.
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Energy Resolved X-ray Imaging as a Tool for Characterization of Paper Coating Quality2009Ingår i: IEEE Nuclear Science Symposium Conference Record 2009, IEEE conference proceedings, 2009, s. 1703-1706Konferensbidrag (Refereegranskat)
    Abstract [en]

    Energy resolved X-ray imaging can be used as a tool to analyze the variation in the chemical content of an object. In this work we have used energy resolved X-ray imaging to measure the variation in the chemical content of paper and paper coating. This is an important quality parameter for the paper industry. In order to separate the variation in coating thickness from the variation in paper thickness, energy resolution is used to separate the response of the coating from the response of the paper. The MEDIPIX2 single photon processing X-ray imaging system [1] has been used in the measurements.  The measurement results are compared to simulations with MCNP. The influence of charge sharing is discussed and the effects have been studied by comparing results from detectors with 220x220 µm2 pixels and detectors with 55x55 µm2 pixels. There is a trade-off between good spatial resolution obtained with detectors with small pixels and good energy resolution obtained with detectors with large pixels. The requirements on image quality, to achieve the resolution of coating distribution relevant for the application, are discussed.

  • 24.
    Norlin, Börje
    et al.
    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.
    Krapohl, David
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Fröjdh, Anna
    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.
    Fröjdh, Christer
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Spectroscopic X-Ray Imaging Using a Pixelated Detector with Single Photon Processing Readout2010Ingår i: Proceedings of 2010 IEEE NUCLEAR SCIENCE SYMPOSIUM CONFERENCE, IEEE conference proceedings, 2010, s. 1074-1078, artikel-id 5873931Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 25.
    Norlin, Börje
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Reza, Salim
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    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, Medipix Consortium, Geneva, Switzerland.
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Readout cross-talk for alpha-particle measurements in a pixelated sensor system2015Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 10, artikel-id C05025Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 26.
    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.

  • 27.
    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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