Assessment of a MEDIPIX2 Detector for Coherent X-ray Diffractive Imaging

Our group is concerned with addressing the limitations of current x-ray imaging devices for Coherent X-ray Diffractive Imaging (CXDI). CCDs are well established in this area of research. However the signal to noise ratio and dynamic range of integrating devices are sub-optimal for CXDI. For successful CXDI image reconstruction the recorded signal should be accurately measured over a wide dynamic range. This is best achieved by measuring precisely the number of photons registered by a pixel. Accurate data sets allow reconstruction algorithms to converge in a shorter time than if noisy estimates of the intensities are used. Using modern very large scale integrated circuit (VLSI) technology complex pixel readout circuitry can be fabricated with a footprint of less than 100 microns square. Placing an x-ray sensitive material above such a circuit matrix and electrically or optically connecting to it, produces a versatile and accurate x-ray detector. The name given to such a device is a hybrid pixel detector (HPD). We have chosen the MEDIPIX2 HPD to assess against the demands of CXDI. This paper reports on laboratory tests of a device with a 300 micron thick silicon as the x-ray converter, and an array of 256 x 256 pixels each of 55 microns square.