miun.sePublications
Change search
Refine search result
1 - 14 of 14
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1. Badel, X.
    et al.
    Linnros, J.
    Kleimann, P.
    Norlin, Börje
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Koskiahde, E.
    Valpas, K.
    Nenonen, S.
    Petersson, Sture
    Department of Microelectronics, Roy. Inst. of Technology of Sweden, Kista.
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Metallized and Oxidized Silicon Macropore Arrays Filled with a Scintillator for CCD-based X-ray Imaging Detectors2004In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 51, no 3 Part 3, p. 1001-1005Article in journal (Refereed)
    Abstract [en]

    Silicon Charge Coupled Devices (CCD)covered with a scintillating film are now available on the market for use in digital medical imaging. However, these devices could still be improved in terms of sensitivity and especially spatial resolution by coating the CCD with an array of scintillating waveguides. In this work, we fabricated such waveguides by first etching pores in silicon, then performing metallization or oxidation of the pore walls and finally filling the pores with CsI(Tl). The resulting structures were observed using SEM and tested under X-ray exposure. The detector performances were also compared with simulations, indicating that the optimal pore depth for metallized macropore arrays is about 80 um while it is around 350 um for oxidized ones. This result, together with the roughness of the metal coating, explains why lower performances were measured experimentally with the metallized macropores. Indeed, our macropore arrays had depths in the range of 210-390 um, which is favorable to oxidized structures.

  • 2.
    Badel, X
    et al.
    KTH.
    Norlin, Börje
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kleimann, P
    Université Claude Bernard Lyon-I, France.
    Williams, L
    Applied Scintillation Technology, United Kingdom.
    Moody, S.J.
    Applied Scintillation Technology, United Kingdom.
    Tyrrell, G.C.
    Applied Scintillation Technology, United Kingdom.
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Linnros, J
    KTH.
    Performance of Scintillating Waveguides for CCD-based X-ray Detectors2006In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 53, no 1, p. 3-8Article in journal (Refereed)
    Abstract [en]

    Scintillating films are usually used to improve the sensitivity of CCD-based X-ray imaging detectors. For an optimal spatial resolution and detection efficiency, a tradeoff has to be made on the film thickness. However, these scintillating layers can also be structured to provide a pixellated screen. In this paper, the study of CsI(Tl)-filled pore arrays is reported. The pores are first etched in silicon, then oxidized and finally filled with CsI(Tl) to form scintillating waveguides. The dependence of the detector sensitivity on pore depth, varied from 40 to 400 µm here, follows rather well theoretical predictions. Most of the detectors produced in this work have a detective quantum efficiency of the incoming X-ray photons of about 25%; however, one detector shows that higher efficiency can be achieved. The comparison of its efficiency to a 1-mm thick CsI(Tl) crystal indicates that light collection efficiency in the guides may approach what is theoretically possible. Imaging capabilities of the detectors are demonstrated.

  • 3.
    Chmeissani, M
    et al.
    IFAE Barcelona .
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Gal, O
    CEA France.
    Llopart, X
    CERN.
    Ludwig, J
    Albert-Ludwigs-Universität-Freiburg.
    Ponchut, C
    ESRF.
    Russo, P
    INFN, Italy.
    Tlustos, L
    CERN.
    First experimental tests with a CdTe photon counting pixel detector hybridized with a Medipix2 readout chip2004In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 51, no 5, p. 2379-2385Article in journal (Refereed)
    Abstract [en]

    We present preliminary tests of hybrid pixel detectors consisting of the Medipix2 readout chip bump-bonded to a 1-mm-thick CdTe pixel detector. This room temperature imaging system for single photon counting has been developed within the Medipix2 European Collaboration for various imaging applications with X-rays and gamma rays, including dental radiography, mammography, synchrotron radiation, nuclear medicine, and radiation monitoring in nuclear facilities. The Medipix2 + CdTe hybrid detector features 256 × 256 square pixels, a pitch of 55 μm, a sensitive area of 14×14 mm2. We analyzed the quality of the detector and bump-bonding and the response to nuclear radiation of the first CdTe hybrids. The CdTe pixel detectors, with Pt ohmic contacts, showed an ohmic response when negatively biased up to less than 60 V (electrons collection mode). Tests were also performed in holes collection mode, where a nonresistive behavior was observed above +15 V. We performed a series of imaging tests at low voltage bias with gamma radioactive sources and with an X-ray tube. Under uniform irradiation, we observed for all detectors the presence of numerous, stable structures in the form of small circles of about 200 μm diameter, with the central pixels showing a reduced counting efficiency with respect to the periphery (in electrons counting regime). Also long filament structures have been observed. Further investigations will reveal whether they are due to an intrinsic detector response (e.g., due to Te inclusions) or to the bump-bonding process.

  • 4. Duan, M.
    et al.
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Wang, W.
    Linnros, J.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Deposition of Scintillating Layers of Bismuth Germanate (BGO) Films for X-ray detector applications1998In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 45, no 3, p. 525-527Article in journal (Refereed)
    Abstract [en]

    Bi4Ge3O12 films were deposited by pulsed laser ablation on glass and SiO2/Si substrates. The crystal structures of the films depend on the deposition temperature. XRD patterns indicate that the films deposited at substrate temperature less than 400°C are amorphous. The as deposited amorphous films can be crystallized by post rapid thermal annealing (RTA) in the temperature window from 750°C to 800°C for 2 minutes in a oxygen ambient environment. RBS measurements confirm that the films have the same chemical composition as that of the target. The surface morphology of the films were characterized by atomic force microscopy (AFM)

  • 5.
    Fröjdh, Christer
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nelvig, P.
    Simulation of the X-ray Response of Scintillator Coated Silicon CCDs1998In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 45, no 3, Pt 1, p. 374-378Article in journal (Refereed)
  • 6.
    Fröjdh, Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. CERN, CH-1211, Geneva, 23, Switzerland .
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Gimenez, E. N.
    Diamond Light Source, Harwell Science and Innovation Campus, Chiltern, Didcot, Oxfordshire, OX11 0QX, United Kingdom .
    Krapohl, David
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Maneuski, D.
    University of Glasgow, Glasgow, G12 8QQ, United Kingdom .
    Norlin, Börje
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    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
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    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 Beam2013In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 60, no 4, p. 2864-2869Article in journal (Refereed)
    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.

  • 7. Irsigler, R
    et al.
    Andersson, J
    Alverbro, J
    Borglind, J
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Helander, P
    Manolopoulos, S
    Martijn, H
    O'Shea, V
    Smith, K M
    X-ray imaging using a 320 x 240 hybrid GaAs pixel detector1999In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 46, no 3, p. 507-512Article in journal (Refereed)
  • 8.
    Kittelmann, T.
    et al.
    European Spallat Source ERIC, Lund.
    Kanaki, K.
    European Spallat Source ERIC, Lund.
    Klinkby, E.
    European Spallat Source ERIC, Lund.
    Cai, X. X.
    European Spallat Source ERIC, Lund; Tech Univ Denmark, DTU Nutech, Roskilde, Denmark.
    Cooper-Jensen, C. P.
    European Spallat Source ERIC, Lund; Uppsala Univ, Dept Phys & Astron, Uppsala.
    Hall-Wilton, Richard
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. European Spallat Source ERIC, Lund.
    Using Backscattering to Enhance Efficiency in Neutron Detectors2017In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 64, no 6, p. 1562-1573, article id 7903709Article in journal (Refereed)
    Abstract [en]

    The principle of using strongly scattering materials to recover efficiency in detectors for neutron instruments, via backscattering of unconverted thermal neutrons, is discussed in general. The feasibility of the method is illustrated through Geant4-based simulations involving thermal neutrons impinging on a specific setup with a layer of polyethylene placed behind a single-layered boron-10 thin-film gaseous detector. The results show that detection efficiencies can be as much as doubled in the most ideal scenario, but with associated adverse contributions to spatial and timing resolutions of, respectively, centimeters and tens of microseconds. Potential mitigation techniques to contain the impact on resolution are investigated and are found to alleviate the issues to some degree, at a cost of reduced gain in efficiency.

    Download full text (pdf)
    fulltext
  • 9.
    Kleimann, P
    et al.
    KTH.
    Linnros, J
    KTH.
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    An x-ray imaging pixel detector based on a scintillating guides screen2000In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 47, no 4, p. 1483-1486Article in journal (Refereed)
  • 10.
    Krapohl, David
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Schubel, Armin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. University of Heidelberg, Heidelberg, Germany.
    Fröjdh, Erik
    Paul Scherrer Institute, Villigen, Switzerland.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. Paul Scherrer Institute, Villigen, Switzerland.
    Validation of Geant4 Pixel Detector Simulation Framework by Measurements with the Medipix Family Detectors2016In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 63, no 3, p. 1874-1881, article id 7497723Article in journal (Refereed)
    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.

  • 11.
    Llopart Cudié, Xavier
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Campbell, M
    Dinapoli, R
    San Segundo, D
    Pernigotti, E
    Medipix2, a 64k pixel readout chip with 55 μm square elements working in single photon counting mode2002In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 49, p. 2279-2283Article in journal (Refereed)
    Abstract [en]

    The Medipix2 chip is a pixel detector readout chip consisting of 256×256 identical elements, each working in single photon counting mode for positive or negative input charge signals. Each pixel cell contains around 500 transistors and occupies a total surface area of 55 μm×55 μm. A 20 μm width octagonal opening connects the detector and the preamplifier input via bump-bonding. The preamplifier feedback provides compensation for detector leakage current on a pixel by pixel basis. Two identical pulse height discriminators are used to create a pulse if the preamplifier output falls within a defined energy window. These digital pulses are then counted with a 13-bit pseudo-random counter. The counter logic, based in a shift register, also behaves as the input/output register for the pixel. Each cell also has an 8-bit configuration register which allows masking, test-enabling and 3-bit individual threshold adjust for each discriminator. The chip can be configured in serial mode and read out either serially or in parallel. The chip is designed and manufactured in a 6-metal 0.25 μm CMOS technology. Preliminary measurements show very good agreement with simulations.

  • 12.
    Nilsson, Hans-Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Monte Carlo simulation of charge sharing effects in silicon and GaAs photon-counting X-ray imaging detectors2004In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 51, no 4, p. 1636-1640Article in journal (Refereed)
    Abstract [en]

    In this work we present a numerical study of charge sharing in photon counting X-ray imaging detectors. The study is based on charge transport simulations combined with a system level Monte Carlo simulation code to calculate the energy resolution of different pixel detector configurations. Our simulations show that the charge sharing is very sensitive to the electric field distribution in the device, and that the higher doping levels used in GaAs detectors reduce the effect of charge sharing significantly. Our study concludes that one of advantage's in using very heavy semiconductor materials in X-ray imaging detectors is the possibility to suppress charge sharing utilizing structures with much higher electric field. A 100 mum thick epitaxial GaAs detector absorbs 52% of the photons, while a 300 pin thick Silicon detector absorbs only 8% of the photons (30keV source). In addition to the superior stopping power, the GaAs detector has 5 times lower charge diffusion, resulting in superior spatial and energy resolution.

  • 13. Tlustos, L
    et al.
    Ballabriga, R
    Campbell, M
    Heijne, E H M
    Kincade, K
    Llopart Cudié, Xavier
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Stejskal, P
    Imaging properties of the Medipix2 system exploiting single and dual enery thresholds2006In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 53, p. 1323-1328Article in journal (Refereed)
    Abstract [en]

    Low noise, high resolution and high dose efficiency are the common requirements for most X-ray imaging applications. Especially in medical applications the dose efficiency is a necessity for detector systems. We present the imaging performance of the Medipix2 readout chip bump bonded to a 300 mu m thick Si detector as a function of the detection threshold, a free parameter not available in conventional integrating imaging systems. Spatial resolution has been measured using the modulation transfer function (MTF) and it varies between 8.2 Ip/mm and 11.0 Ip/mm at 70%. An associated measurement of noise power spectrum (NPS) permits us to derive the detective quantum efficiency (DQE) which can be as a high as 25.5 % for a broadband incoming spectrum. The influence of charge diffusion in the sensor together with threshold variation in the readout chip is discussed. Although the Medipix2 system is used in photon counting mode with a single threshold in energy, the system is also capable of counting within a given energy window of down to ~1.4 keV. First measurements and images using this feature reveal capabilities that allow to identify fluorescence and other sources of disturbance.

  • 14. Tlustos, L
    et al.
    Campbell, M
    Heijne, E H M
    Llopart Cudié, Xavier
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Signal variations in high granularity Si pixel detectors2004In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 51, p. 3006-3012Article in journal (Refereed)
    Abstract [en]

    Fixed pattern noise is one of the limiting factors of image quality and degrades the achievable spatial resolution. In the case of silicon sensors non-uniformities due to doping inhomogeneities can be limited by operating the sensor in strong overdepletion. For high granularity photon counting pixel detectors an additional high frequency interpixel signal variation is an important factor for the achievable signal to noise ratio (SNR). It is common practice to apply flatfield corrections to increase the SNR of the detector system. For the case of direct conversion detectors it can be shown that the Poisson limit can be reached for floodfield irradiation. However when used for imaging with spectral X-ray sources flatfield corrections are less effective. This is partly a consequence of charge sharing between adjacent pixels, which gives rise to an effective energy spectrum seen by the readout, which is different from the spectral content of the incident beam. In this paper we present simulations and measurements of the limited applicability of flatfield corrections for spectral source imaging and investigate the origins of the high frequency interpixel noise component The model, calculations and measurements performed suggest that flatfield correction maps for photon counting detectors with a direct conversion Si sensor can be obtained from electrical characterization of the readout chip alone.

1 - 14 of 14
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf