Yazar "Shokr, Mohammad Mahdi" seçeneğine göre listele

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  • Küçük Resim
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    A new spectroscopic imager for X-rays from 0.5 keV to 150 keV combining a pnCCD and a columnar CsI(Tl) scintillator
    (Iop Publishing Ltd, 2017) Schlosser, Dieter Michael; Hartmann, Robert; Kalok, D.; Bechteler, A.; Abboud, Ali; Shokr, Mohammad Mahdi; Strüeder, Lothar; Çonka Yıldız, Tuba
    By combining a low noise fully depleted pnCCD detector with a columnar CsI(Tl) scintillator an energy dispersive spatial resolving detector can be realized with a high quantum efficiency in the range from below 0.5 keV to above 150 keV. The used scintillator system increases the pulse height of gamma-rays converted in the CsI(Tl), due to focusing properties of the columnar scintillator structure by reducing the event size in indirect detection mode (conversion in the scintillator). In case of direct detection (conversion in the silicon of the pnCCD) the relative energy resolution is 0.7% at 122 keV (FWHM = 850 eV) and the spatial resolution is less than 75 mu m. In case of indirect detection the relative energy resolution, integrated over all event sizes is about 9% at 122 keV with an expected spatial precision of below 75 mu m.
  • Küçük Resim
    Öğe
    Application of a pnCCD for energy-dispersive Lauc diffraction with ultra-hard X-rays
    (Int Union Crystallography, 2015) Send, Sebastian; Abboud, Ali; Wiesner, Nadja; Shokr, Mohammad Mahdi; Çonka Yıldız, Tuba; Klaus, Manuela; Hartmann, Robert
    In this work the spectroscopic performance of a pnCCD detector in the ultra-hard energy range between 40 and 140 keV is tested by means of an energy-dispersive Laue diffraction experiment on a GaAs crystal. About 100 Bragg peaks were collected in a single-shot exposure of the arbitrarily oriented sample to white synchrotron radiation provided by a wiggler at BESSY II and resolved in a large reciprocal-space volume. The positions and energies of individual Laue spots could be determined with a spatial accuracy of less than one pixel and a relative energy resolution better than 1%. In this way the unit-cell parameters of GaAs were extracted with an accuracy of 0.5%, allowing for a complete indexing of the recorded Laue pattern. Despite the low quantum efficiency of the pnCCD (below 7%), experimental structure factors could be obtained from the three-dimensional data sets, taking into account photoelectric absorption as well as Compton scattering processes inside the detector. The agreement between measured and theoretical kinematical structure factors calculated from the known crystal structure is of the order of 10%. The results of this experiment demonstrate the potential of pnCCD detectors for applications in X-ray structure analysis using the complete energy spectrum of synchrotron radiation.
  • [ X ]
    Öğe
    Applications of a pnCCD detector coupled to columnar structure CsI(Tl) scintillator system in ultra high energy X-ray Laue diffraction
    (Iop Publishing Ltd, 2017) Shokr, Mohammad Mahdi; Schlosser, Dieter Michael; Abboud, Ali; Algashi, Alaa; Tosson, Amir; Çonka Yıldız, Tuba; Pietsch, Ullrich
    Most charge coupled devices (CCDs) are made of silicon (Si) with typical active layer thicknesses of several microns. In case of a pnCCD detector the sensitive Si thickness is 450 mu m. However, for silicon based detectors the quantum efficiency for hard X-rays drops significantly for photon energies above 10 keV. This drawback can be overcome by combining a pixelated silicon-based detector system with a columnar scintillator. Here we report on the characterization of a low noise, fully depleted 128 x 128 pixels pnCCD detector with 75 x 75 mu m(2) pixel size coupled to a 700 mu m thick columnar CsI(Tl) scintillator in the photon range between 1 keV to 130 keV. The excellent performance of the detection system in the hard X-ray range is demonstrated in a Laue type X-ray diffraction experiment performed at EDDI beamline of the BESSY II synchrotron taken at a set of several GaAs single crystals irradiated by white synchrotron radiation. With the columnar structure of the scintillator, the position resolution of the whole system reaches a value of less than one pixel. Using the presented detector system and considering the functional relation between indirect and direct photon events Laue diffraction peaks with X-ray energies up to 120 keV were efficiently detected. As one of possible applications of the combined CsI-pnCCD system we demonstrate that the accuracy of X-ray structure factors extracted from Laue diffraction peaks can be significantly improved in hard X-ray range using the combined CsI(Tl)-pnCCD system compared to a bare pnCCD.