Showing papers by "Michael Fiederle published in 2012"
TL;DR: The imaging properties of Medipix2 MXR multi-chip assemblies bump bonded to 1 mm thick CdTe sensors are described and the finding that higher maximum count rates come at the cost of a reduced energy resolution is concluded.
Abstract: Spectroscopic x-ray imaging by means of photon counting detectors has received growing interest during the past years. Critical to the image quality of such devices is their pixel pitch and the sensor material employed. This paper describes the imaging properties of Medipix2 MXR multi-chip assemblies bump bonded to 1 mm thick CdTe sensors. Two systems were investigated with pixel pitches of 110 and 165 μm, which are in the order of the mean free path lengths of the characteristic x-rays produced in their sensors. Peak widths were found to be almost constant across the energy range of 10 to 60 keV, with values of 2.3 and 2.2 keV (FWHM) for the two pixel pitches. The average number of pixels responding to a single incoming photon are about 1.85 and 1.45 at 60 keV, amounting to detective quantum efficiencies of 0.77 and 0.84 at a spatial frequency of zero. Energy selective CT acquisitions are presented, and the two pixel pitches' abilities to discriminate between iodine and gadolinium contrast agents are examined. It is shown that the choice of the pixel pitch translates into a minimum contrast agent concentration for which material discrimination is still possible. We finally investigate saturation effects at high x-ray fluxes and conclude with the finding that higher maximum count rates come at the cost of a reduced energy resolution.
96 citations
TL;DR: In this article, the authors investigated the impact of uncompensated impurities on the detection efficiency of CdTe and Cd0.9Zn0.1Te Schottky diodes.
Abstract: In this paper we report on the strong impact of the concentration of uncompensated impurities on the detection efficiency of CdTe and Cd0.9Zn0.1Te Schottky diodes. The results of our study explain the observed poor detection properties of some Cd0.9Zn0.1Te detectors with resistivity and lifetime of carriers comparable to those of good CdTe detectors. We show that the concentration of uncompensated impurities in a highly efficient CdTe Schottky diode detector is several orders of magnitude higher than that of a CdZnTe, which does not register the gamma spectra of commonly used isotopes (59–662 keV) by using photoelectric measurements. The significant difference of the concentration of uncompensated impurities between CdTe and Cd0.9Zn0.1Te crystals is confirmed by our study of the temperature change of the resistivity and of the Fermi level energy. The degree of compensation of the donor complex, responsible for the electrical conductivity of the material, is much lower in the CdTe crystal compared to that in the Cd0.9Zn0.1Te crystal. The calculations of the detection efficiency of x/γ-radiation by a Schottky diode result in a dependence on the concentration of uncompensated impurities described by a curve with a pronounced maximum. The position of this maximum occurs at a concentration of uncompensated impurities which ranges from 3 × 1010 to 3 × 1012 cm−3 depending on the registered photon energy of x/γ-rays and on the lifetime of the charge carriers. Our measurements and calculations lead to the conclusion that the concentration of uncompensated impurities in this range is a necessary condition for the effective operation of x- and γ-ray Schottky diode detectors based on CdTe and Cd1−xZnxTe crystals.
26 citations
TL;DR: Chen et al. as discussed by the authors proposed a CZT detector array with improved sensitivity for medical imaging and homeland security applications, which achieved uniformity of charge collection efficiency with THM grown CdZnTe crystals.
Abstract: ix Conference Committee xiii Introduction SESSION 1 CZT DETECTORS I 7449 02 CZT device with improved sensitivity for medical imaging and homeland security applications (Invited Paper) [7449-01] H. Chen, S. A. Awadalla, P. Marthandam, K. Iniewski, P. H. Lu, G. Bindley, Redlen Technologies (Canada) 7449 04 Dual anode contact geometries for x-ray and gamma-ray spectroscopy and 3D localization [7449-03] J.W. Martin, A. B. Garson III, Q. Li, K. Lee, Washington Univ. in St. Louis (United States); M. Groza, V. Buliga, A. Burger, Fisk Univ. (Uni ted States); H. Krawczynski, Washington Univ. in St. Louis (United States) 7449 05 Front-end ASIC for pixilated wide bandgap detectors [7449-04] E. Vernon, G. De Geronimo, J. Fried, Brookhaven National Lab. (United States); C. Herman, F. Zhang, Z. He, Univ. of Michigan, Ann Arbor (United States) SESSION 2 CZT CHARACTERIZATION I 7449 08 Uniformity of charge collection efficiency in Frisch collar spectrometer with THM grown CdZnTe crystals [7449-07] A. Kargar, A. C. Brooks, Kansas State Univ. (U nited States); M. J. Harrison, Univ. of Florida (United States); H. Chen, S. Awadalla, G. Bindley, B. Redden, Redlen Technologies (Canada); D. S. McGregor, Kansas State Univ. (United States) SESSION 3 CZT DETECTORS II 7449 09 Characterization of a 15-mm-long virtual Frisch-grid CZT detector array (Invited Paper) [7449-08] A. E. Bolotnikov, Brookhaven National Lab. (U nited States); S. Babalola, Fisk Univ. (United States) and Vanderbilt Univ. (United States); G. S. Camarda, Y. Cui, Brookhaven National Lab. (United States); S. U. Egarievwe, Fisk Univ. (United States); P. M. Fochuk, Chernivtsi National Univ. (Ukraine); M. Hirt, Univ. of Mi chigan (United States); A. Hossain, K. Kim, Brookhaven National Lab. (United States); O. V. Kopach, Chernivtsi National Univ. (Ukraine); N. D. Sferrazza, Brookhaven National Lab. (United States); J. Sturgess, Vanderbilt Univ. (United States); K. Polack, Univ. of Michigan (United States); B. Raghothamachar, Stony Brook Univ. (United States); G. Yang, R. B. Ja mes, Brookhaven National Lab. (United States)
14 citations
TL;DR: In this article, the authors investigated the thermal activation energy of Cd0.9Zn0.1Te and found that the donor level dominates in the conductivity of the material and its compensation is virtually complete (Na/Nd) as predicted by theory.
Abstract: Cd0.9Zn0.1Te:In crystals with semi-intrinsic conductivity have been investigated. Temperature dependence of their electrical characteristics shows a number of unconventional peculiarities: the thermal activation energy of conductivity is “anomalously” low (0.60–0.62 eV); the resistivity at elevated temperatures is greater than its intrinsic value for Cd0.9Zn0.1Te; the inversion of the conduction from n- to p-type occurs at a temperature slightly above 300 K, etc. The observed features are explained in terms of statistics of electrons and holes in a semiconductor containing a self-compensation complex, whose concentration is much higher than those of uncontrolled (background) impurities and defects. Comparison of the calculation results and experimental data leads to the conclusion that the donor level, which is far distant from the middle of the band gap, dominates in the conductivity of the material and its compensation is virtually complete (Na/Nd = 0.99996–0.99998) as predicted by theory.
6 citations
TL;DR: In this article, the photoconductivity (PC) measurements of Cd 1-x Zn x Te (x = 0.1) crystals from two different manufacturers were studied by PC measurements.
Abstract: The Cd 1-x Zn x Te ( x = 0.1) crystals from two different manufacturers were studied by photoconductivity (PC) measurements. The samples 1 and 2 were subjected to chemical etching and irradiation with nanosecond laser pulses. The IR transmittance spectra of the crystals before and after laser irradiation were also monitored. The PC spectrum of the sample 1 had a typical one-band shape while the spectrum of the sample 2 exhibited two bands roughly corresponding to the bandgaps of CdTe and Cd 1-x Zn x Te that could be attributed to inhomogeneities in the surface region of the crystal. The positions of the maximum and red edge of the PC spectra did not correspond to the component compositions x in the bulk of Cd 0.9 Zn 0.1 Te crystals, however chemical polishing etching of the samples in a brominemethanol solution or/and laser irradiation led to this correspondence. Moreover, depending of laser pulse energy density, irradiation of Cd 1-x Zn x Te crystals resulted in a short-wavelength shift of the PC spectra, transformation of two bands to one in the case of the sample 2, and an increase in the photosensitivity of the semiconductor. The laser processing provided equalization of parameters in the surface and bulk regions.
4 citations
Patent•
23 Nov 2012TL;DR: In this paper, a detector and a method for the detection of ionising radiation are proposed, which exhibits a detector body made from a semiconductor material in which incident ionizing radiation generates free electron-hole pairs, a cathode side ( 4 ) of the detector body ( 2 ) to which the free holes generated drift in an electric field.
Abstract: A detector and a method for the detection of ionising radiation are proposed. The detector ( 1 ) exhibits a detector body ( 2 ) made from a semiconductor material in which incident ionising radiation generates free electron-hole pairs, a cathode side ( 4 ) of the detector body ( 2 ) to which the free holes generated drift in an electric field, an anode side ( 3 ) of the detector body ( 2 ) to which the free electrons generated drift in an electric field, at least two electrodes ( 5, 6 ) on the anode side ( 3 ) and at least two electrodes ( 7, 8 ) on the cathode side ( 4 ). There is a potential difference between the electrodes ( 5, 6, 7, 8 ). The potential difference between the individual electrodes ( 7, 8 ) on the cathode side ( 4 ) is smaller than the potential difference between each of the electrodes ( 5, 6 ) on the anode side ( 3 ) on the one hand and each of the electrodes ( 7, 8 ) on the cathode side ( 4 ) on the other hand. As a result of irradiation of the detector body ( 2 ) with ionising radiation, electron-hole pairs are generated in the detector body ( 2 ). Signals are detected at the electrodes ( 7, 8 ) on the cathode side. The difference is calculated and evaluated from these signals.
3 citations
01 Oct 2012
TL;DR: In this paper, the suitability of thin Eu2+ activated SrI2-screens for X-ray radiography applications was tested and a packaging technique was developed that protected the hygroscopic screens during measurements.
Abstract: The Eu2+ activated SrI2 is gaining ground in spectroscopic applications, thanks to its excellent scintillation properties like high light yield and good energy resolution. The exploitation of these properties for other application fields is limited by the hygroscopic nature of the SrI2. Single crystal scintillating screens exhibit high spatial resolution, this combined with the high density, high effective atomic number, and the high light yield of the SrI2 could be used for high resolution X-ray imaging. In this work, the suitability of thin SrI2-screens for Xray radiography applications was tested. First a packaging technique was developed that protected the hygroscopic screens during measurements. Our results show high resolution of the images obtained with thin SrI2-scintillator screens. With these results, we think that the SrI2-scinitillator is not only a candidate for spectroscopic applications, but also for high resolution X-ray imaging applications.
3 citations
TL;DR: In this article, measurements with Medipix2 MXR detectors attached to CdTe sensors with pixel pitches of 110 and 165 μm were carried out at the Topo-Tomo beamline of the ANKA synchrotron at the Karlsruhe Institute of Technology (KIT).
Abstract: The energy resolution of photon counting pixel detectors depends strongly on the pixel pitch Small pixels increase the effects of characteristic X-rays and the sharing of charges between adjacent pixels To investigate the effects of different pixel pitches, measurements with Medipix2 MXR detectors attached to CdTe sensors with pixel pitches of 110 and 165 μm were carried out at the Topo-Tomo beamline of the ANKA synchrotron at the Karlsruhe Institute of Technology (KIT) Photo peaks are measured at a number of energies and are used to calculate the fraction of events in the photo peak compared to the total Finally, we investigate the linearity of the energy calibration curves as a function of the pixel pitch
3 citations
TL;DR: In this paper, a 0.314 cm3 SrI2:Eu (6 mol%) single crystal was grown in silica ampoule to prevent hydration and oxygen contamination using the vertical Bridgman technique.
Abstract: Much work is going on presently to improve the crystal growth and packaging of the Eu2+ activated SrI2 scintillator, thanks to its excellent scintillation properties like high light yield and good energy resolution. Larger crystals are needed for spectroscopic applications, and proper packaging is important for long-time field use and application in other areas due to its hygroscopic nature. In this paper, we report on the successful growth of a SrI2:Eu [6 mol%] single crystal in silica ampoule to prevent melt hydration and oxygen contamination using the vertical Bridgman technique. The scintillation properties of a 0.314 cm3 SrI2:Eu sample are presented, showing a light output of ~80 000 ph/MeV . A 360 μm sample was investigated for X-ray imaging applications; we also show how the sample was prepared for the measurement and the result of this preliminary investigation.
3 citations
01 Oct 2012
TL;DR: In this paper, the authors focus on the evaluation of spectroscopic background radiation measurements performed at an outdoor facility on the Schauinsland mountain in Germany using two temperature stabilized Coplanar Grid (Cd,Zn)Te detectors together with a custom digital multi-channel analyzer.
Abstract: This work focuses on the evaluation of spectroscopic background radiation measurements performed at an outdoor facility on the Schauinsland mountain in Germany The detector system that was used consisted of two temperature stabilized Coplanar Grid (Cd,Zn)Te detectors together with a custom digital Multi Channel Analyzer The research presented includes the evaluation of the spectroscopic outdoor performance, the analysis of the correlation of count rates in certain energy regions with meteorological factors and the quantification of the temperature stability
3 citations
Patent•
23 Nov 2012TL;DR: In this paper, the main portion of the detector is made of semiconductor material in which incident ionizing radiation generates free electron-hole pairs which drift in electric field with anode and cathode sides (3,4) of main portion.
Abstract: The detector (1) has detector main portion (2) that is made of semiconductor material in which incident ionizing radiation generates free electron-hole pairs which drift in electric field with anode and cathode sides (3,4) of main portion. Sections of the first and second electrodes are arranged next to each other on cathode side and extend across entire cathode side. The potential difference between the first and second electrodes on the cathode side is smaller than the potential difference between third and fourth electrodes (5,6) on the anode side. An independent claim is included for method for detection of ionizing radiation.
01 Oct 2012
TL;DR: A novel method which uses hole drift times in Coplanar Grid detectors to determine the interaction depth and identify multi-hit events is presented.
Abstract: We present a novel method which uses hole drift times in Coplanar Grid detectors to determine the interaction depth and identify multi-hit events Theoretical considerations in chapter II explain the method, furthermore a simple simulation is introduced Chapter III introduces a modified Coplanar Grid detector Chapters IV and V show and discuss experimental results regarding the drift time dependent depth correction
TL;DR: In this paper, the extrinsic molecular doping of zinc oxide (ZnO) thin films grown by plasma enhanced molecular beam epitaxy (P-MBE) was investigated, and the dopant was thermally evaporated arsenic trioxide (formula: As2O3 in the solid state), which appeared as As4O6 molecule in the gaseous phase.
Abstract: This work investigates the extrinsic molecular doping of zinc oxide (ZnO) thin films grown by plasma enhanced molecular beam epitaxy (P-MBE). The dopant was thermally evaporated arsenic trioxide (formula: As2O3 in the solid state), which appears as As4O6 molecule in the gaseous phase. Cracking experiments of these As4O6 molecules were made using a radio frequency oxygen plasma. Structural, chemical and optical investigations were made with (High Resolution) X-ray diffraction (HRXRD), secondary ion mass spectroscopy (SIMS) and photoluminescence (PL). These results show high incorporation rates (about 2x1018 cm-3) and optical activity of the dopant. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)