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Instruments / Technical Area	Publication Details	Published
B16-Test Beamline	Investigating the suitability of GaAs:Cr material for high flux X-ray imaging Matt Veale , Steven Bell , Diana Duarte , Marcus French , Matthew Hart , Andreas Schneider , Paul Seller , Matthew Wilson , Slava Kachkanov , A D Lozinskaya , V A Novikov , O P Tolbanov , A. Tyazhev , A N Zarubin Journal Of Instrumentation 9, C12047 - C12047 16th International Workshop on Radiation Imaging Detectors DOI: 10.1088/1748-0221/9/12/C12047 Diamond Proposal Number(s): [4984] Open Access Show Abstract ▼ Abstract: Semi-insulating wafers of GaAs material with a thickness of 500 micrometres have been compensated with chromium by Tomsk State University. Initial measurements have shown the material to have high resistivity (3 × 10[9] ohm cm) and tests with pixel detectors on a 250 micrometres pitch produced uniform spectroscopic performance across an 80 × 80 pixel array. At present, there is a lack of detectors that are capable of operating at high X-ray fluxes (> 10^8 photons s-1 mm-2) in the energy range 550 keV. Under these conditions, the poor stopping power of silicon, as well as issues with radiation hardness, severely degrade the performance of traditional detectors. While high-Z materials such as CdTe and CdZnTe may have much greater stopping power, the formation of space charge within these detectors degrades detector performance. Initial measurements made with GaAs:Cr detectors suggest that many of its material properties make it suitable for these challenging conditions. In this paper the radiation hardness of the GaAs:Cr material has been measured on the B16 beam line at the Diamond Light Source synchrotron. Small pixel detectors were bonded to the STFC Hexitec ASIC and were irradiated with 3 × 10^8 photons s-1 mm-2 monochromatic 12 keV X-rays up to a maximum dose of 0.6 MGy. Measurements of the spectroscopic performance before and after irradiation have been used to assess the extent of the radiation damage.	Dec 2014
	Edge effects in a small pixel CdTe for X-ray imaging Diana Duarte , Steven Bell , John Lipp , Andreas Schneider , Paul Seller , Matt Veale , Matthew Wilson , M A Baker , Paul Sellin , Vyacheslav Kachkanov , Kawal Sawhney Journal Of Instrumentation 8, P10018 - P10018 DOI: 10.1088/1748-0221/8/10/P10018 Show Abstract ▼ Abstract: Large area detectors capable of operating with high detection efficiency at energies above 30 keV are required in many contemporary X-ray imaging applications. The properties of high Z compound semiconductors, such as CdTe, make them ideally suitable to these applications. The STFC Rutherford Appleton Laboratory has developed a small pixel CdTe detector with 80 × 80 pixels on a 250 ?m pitch. Historically, these detectors have included a 200 ?m wide guard band around the pixelated anode to reduce the effect of defects in the crystal edge. The latest version of the detector ASIC is capable of four-side butting that allows the tiling of N × N flat panel arrays. To limit the dead space between modules to the width of one pixel, edgeless detector geometries have been developed where the active volume of the detector extends to the physical edge of the crystal. The spectroscopic performance of an edgeless CdTe detector bump bonded to the HEXITEC ASIC was tested with sealed radiation sources and compared with a monochromatic X-ray micro-beam mapping measurements made at the Diamond Light Source, U.K. The average energy resolution at 59.54 keV of bulk and edge pixels was 1.23 keV and 1.58 keV, respectively. 87% of the edge pixels present fully spectroscopic performance demonstrating that edgeless CdTe detectors are a promising technology for the production of large panel radiation detectors for X-ray imaging.	Oct 2013
B16-Test Beamline	Synchrotron Characterisation of Non-Uniformities in a Small Pixel Cadmium Zinc Telluride Imaging Detector M. C. Veale , S. J. Bell , D. D. Duarte , A. Schneider , P. Seller , M. D. Wilson , V. Kachkanov , K. J. S. Sawhney Nuclear Instruments And Methods In Physics Research Section A: Accelerators, Spectrometers, Detectors And Associated Equipment DOI: 10.1016/j.nima.2013.07.054 Show Abstract ▼ Abstract: A small pixel cadmium zinc telluride detector has been fabricated, assembled and tested at the Rutherford Appleton Laboratory. The detector consists of 74×74 pixels on a 250 ?m pitch with a 50 ?m spacing. Flat field irradiations with an 241Am ?-ray source have demonstrated that there are significant variations in the number of counts detected by each pixel as well as large differences in the FWHM of the X-ray photo-peak. A 10×10 ?m microbeam of 20 keV X-rays has been used to characterise these non-uniformities. These measurements have shown that variations in the counting and spectroscopic performance of individual pixels are due to the presence of a non-uniform electric field within the detector	Jul 2013

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