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Instruments / Technical Area	Publication Details	Published
Detectors	Characterisation of the Medipix3 detector for 60 and 80 keV electrons J. A. Mir , R. Clough , R. Macinnes , C. Gough , R. Plackett , I. Shipsey , H. Sawada , I. Maclaren , R. Ballabriga , D. Maneuski , V. O'Shea , D. Mcgrouther , A. I. Kirkland Ultramicroscopy DOI: 10.1016/j.ultramic.2017.06.010 Open Access Show Abstract ▼ Abstract: In this paper we report quantitative measurements of the imaging performance for the current generation of hybrid pixel detector, Medipix3, used as a direct electron detector. We have measured the modulation transfer function and detective quantum efficiency at beam energies of 60 & 80 keV. In single pixel mode, energy threshold values can be chosen to maximize either the modulation transfer function or the detective quantum efficiency, obtaining values near to, or exceeding those for a theoretical detector with square pixels. The Medipix3 charge summing mode delivers simultaneous, high values of both modulation transfer function and detective quantum efficiency. We have also characterized the detector response to single electron events and describe an empirical model that predicts the detector modulation transfer function and detective quantum efficiency based on energy threshold. Exemplifying our findings we demonstrate the Medipix3 imaging performance recording a fully exposed electron diffraction pattern at 24-bit depth together with images in single pixel and charge summing modes. Our findings highlight that for transmission electron microscopy performed at low energies (energies <100 keV) thick hybrid pixel detectors provide an advantageous architecture for direct electron imaging.	Jun 2017
	Review of hybrid pixel detector readout ASICs for spectroscopic X-ray imaging R. Ballabriga , J. Alozy , M. Campbell , E. Frojdh , E. H. M. Heijne , T. Koenig , X. Llopart , J. Marchal , D Pennicard , T. Poikela , L. Tlustos , P. Valerio , W. Wong , M. Zuber Journal Of Instrumentation 11, P01007 - P01007 DOI: 10.1088/1748-0221/11/01/P01007 Open Access Show Abstract ▼ Abstract: Semiconductor detector readout chips with pulse processing electronics have made possible spectroscopic X-ray imaging, bringing an improvement in the overall image quality and, in the case of medical imaging, a reduction in the X-ray dose delivered to the patient. In this contribution we review the state of the art in semiconductor-detector readout ASICs for spectroscopic X-ray imaging with emphasis on hybrid pixel detector technology. We discuss how some of the key challenges of the technology (such as dealing with high fluxes, maintaining spectral fidelity, power consumption density) are addressed by the various ASICs. In order to understand the fundamental limits of the technology, the physics of the interaction of radiation with the semiconductor detector and the process of signal induction in the input electrodes of the readout circuit are described. Simulations of the process of signal induction are presented that reveal the importance of making use of the small pixel effect to minimize the impact of the slow motion of holes and hole trapping in the induced signal in high-Z sensor materials. This can contribute to preserve fidelity in the measured spectrum with relatively short values of the shaper peaking time. Simulations also show, on the other hand, the distortion in the energy spectrum due to charge sharing and fluorescence photons when the pixel pitch is decreased. However, using recent measurements from the Medipix3 ASIC, we demonstrate that the spectroscopic information contained in the incoming photon beam can be recovered by the implementation in hardware of an algorithm whereby the signal from a single photon is reconstructed and allocated to the pixel with the largest deposition.	Jan 2016
B16-Test Beamline Detectors	Medipix3RX: characterizing the Medipix3 redesign with synchrotron radiation Eva Gimenez-Navarro , Rafael Ballabriga , Gabriel Blaj , Michael Campbell , Igor Dolbnya , Erik Frodjh , Ian Horswell , Xavier Llopart-Cudie , Julien Marchal , John Mcgrath , David Omar , Richard Plackett , Kawal Sawhney , Nicola Tartoni Ieee Transactions On Nuclear Science 62 (3), 1413 - 1421 DOI: 10.1109/TNS.2015.2425227 Show Abstract ▼ Abstract: The Medipix3RX is the latest version of the Medipix3 photon counting ASICs, which implements two new operational modes, with respect to the Medipix2 ASIC, aimed at eliminating charge shared events (referred to as Charge Summing Mode (CSM)) and at providing spectroscopic information (referred to as Colour Mode (CM)). The Medipix3RX is a redesign of the Medipix3v0 ASIC and corrects for the underperformance of CSM features observed in the previous version. This paper presents the results from synchrotron X-rays tests to evaluate the Medipix3RX ASIC performance. The newly implemented CSM algorithm eliminates the charge sharing effect at the same time as allocating the event to the readout pixel corresponding to the sensor pixel where the X-ray photon impinged. The new pixel trimming circuit led to a reduced dispersion between pixels. Further results of the linearity for all the gain modes, energy resolution and pixel uniformity are also presented.	Jun 2015

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