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This work presents the design and development of a CdTe sensor, Medipix3RXv2 readout ASICs photocounting detector of 55 pm pixel size arranged in an arc modular distribution for its use in X-ray Pair Distribution Function (PDF) applications at the Diamond Light Source (DLS) synchrotron. This contribution highlights the concept and technical solutions adopted for this new detector which include the development of a fibre optic link between the detector head and the readout FPGA cards. This solution enables a considerable reduction in the weight and size of the detector head.

The Timepix3 ASIC can be used very effectively for time resolved experiments at synchrotron facilities. We have carried out characterizations with the synchrotron beam in order to determine the time resolution and other characteristics such as the energy resolution, charge sharing and signals overlapping. The best time resolution achieved is 19 ns FWHM for 12 keV photons and 350 V bias voltage. The time resolution shows dependency on the photon energy as well as on the chip and acquisition parameters.

This paper focuses on the evaluation of operational conditions such as temperature, exposure time and flux on the polarization of a Schottky electron collection CdTe detector. A Schottky ${\rm e}^ - $ collection CdTe Medipix3RX hybrid pixel detector was developed as a part of the CALIPSO-HIZPAD2 EU project. The $128 \times 128$ pixel matrix and 0.75 mm thick CdTe sensor bump-bonded to Medipix3RX readout chips enabled the study of the polarization effects. Single and quad module Medipix3RX chips were used which had $128 \times 128$ and $256 \times 256$ pixel matrices, respectively. This study reports the sensor-level and pixel-level polarization effects of the detector obtained from a laboratory X-ray source. We report that the sensor-level polarization is highly dependent on temperature, flux and exposure time. Furthermore, the study of pixel-level polarization effects led to identification of a new type of pixel behaviour that is characterised by three distinct phases and, thus, named “tri-phase” (3-P) pixels. The 3-P pixels were the dominant cause of degradation of the flat-field image uniformity under high flux operation. A new method of identifying the optimum operational conditions that utilises a criterion related to the 3-P pixels is proposed. A generated optimum operational conditions chart under the new method is reported. The criterion is used for bias voltage reset depolarization of the detector. The method successfully represented the dependency of polarization on temperature, flux and exposure time and was reproducible for multiple sensors. Operating the detector under the 3-P pixel criterion resulted in the total efficiency not falling below 95%.

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.

A multichip CdTe-Medipix3RX detector system was developed in order to bring the advantages of photon-counting detectors to applications in the hard X-ray range of energies. The detector head consisted of 2×2 Medipix3RX ASICs bump-bonded to a 28 mm×28 mm e − collection Schottky contact CdTe sensor. Schottky CdTe sensors undergo performance degrading polarization which increases with temperature, flux and the longer the HV is applied. Keeping the temperature stable and periodically refreshing the high voltage bias supply was used to minimize the polarization and achieve a stable and reproducible detector response. This leads to good quality images and successful results on the energy resolving capabilities of the system.

A three million pixel photon counting large area detector has been commissioned for the coherent diffraction imaging beamline (I13) of Diamond Light Source. Challenging requirements of small pixel size, large area and fast frame rates required the construction of a detector based upon a tiling of a large number of the latest generation of the Medipix family of photon counting ASICs, Medipix3RX and a highly parallel readout system based upon the Front End Module cards developed by STFC. Such a detector provides a significant improvement in field of view whilst maintaining the resolution afforded by the small pixel size, when compared to previously available Medipix-based detectors such as the quad-chip Merlin. A number of commissioning experiments have been performed on the beamline, and this Conference Record provides intial results from these measurements and determines the capabilities of the detector and beamline system.

This study focuses on Monte Carlo (MC) based techniques to calculate the system matrix (SM) for iterative image reconstruction of small animal PET data. For most PET scanners, the calculation of the SM requires extremely long simulation times due to the large number of image voxels, even when considering symmetries. Our goal is to determine in advance which simplifications can be done to accelerate the MC simulation without jeopardizing the accuracy of the SM. Our small animal scanner prototype was simulated using GATE. It consists of a continuous LSO crystal (42×42×10 mm 3 ) attached to Flat Panel position sensitive photomultipliers. We investigated three different radioactivity distribution models to compute the SM elements for five representative voxel positions. The results show that the simulation time required to compute the whole SM and the accuracy of the SM depend on the model and on the voxel position. In the inner region of the field of view (FOV), the model with eight point sources distributed within each voxel yields the best trade-off between simulation time and SM accuracy. Whereas, for the peripheral region of the FOV, the model with one emission point at the center of the voxel yields the best compromise. The analysis was carried out with and without having depth-of-interaction (DOI) into account. The effect of the distribution model is more significant when DOI is considered.

We have studied a new and inexpensive method of measuring the depth of interaction (DOI) in /spl gamma/-ray detectors with large-sized scintillation crystals. This method takes advantage of the strong correlation between the width of the undisturbed light-distribution in continuous crystals and the /spl gamma/-ray's DOI. In order to quantify the dependence of the distribution's width with respect to the DOI, we first studied an analytical model of the light-distribution and tested it by means of Monte Carlo (MC) simulations of the light transport inside the crystal. Further we present an inexpensive modification of the commonly used charge division circuit that allows analog and instantaneous computation of the light-distribution's second moment without affecting the determination of the centroid. This redesigned resistor network is based on the position-sensitive proportional counter (DPC) readout and allows, together with position sensitive photo-detectors, the additional measurement of the light-distribution's standard-deviation /spl sigma/. We tested the proposed circuit using the design-tool OrCAD and found the signal sufficiently large for digitalization. Finally, we conducted MC simulations of a realistic Positron Emission Tomography (PET) detector module setup that mimic a continuous Lu/sub 2/SiO/sub 5/:Ce/sup 3+/ (LSO) crystal of dimensions 40/spl times/40/spl times/10 mm/sup 3/ together with the new large area position-sensitive photo multiplier tube (PSPMT) H8500 from Hamamatsu. The influence of Compton scattering on the DOI determination was also estimated by MC simulations. Altogether, we obtained /spl les/ 5 mm DOI resolution. PACS: 87.57.Ce, 87.58.Fg, 87.62.+n, 07.85.-m.

We have developed a mini gamma camera based on the new “flat-panel”-type multianode PSPMT (H8500) from Hamamatsu Photonics. The gamma camera is intended for intra-surgical use. The dimensions of the camera are 14 cm×7 cm×7 cm, with a useful field of view of 44 mm, and a weight of 1.2 kg. Its intrinsic resolution is better than 1.5 mm and its energy resolution is about 13%, when using a CsI(Na) scintillating crystal. We present here the most important performance features of the camera and the image reconstruction process followed. Several clinical tests, on breast cancer and melanoma patients, were performed and compared with conventional cameras, to check the quality of the camera. For an administered dose of 3 mCi of 99mTc around the tumour, 1 h before the lymphscintigraphy, we take high-quality images of the nodes in about 30 s using a pinhole collimator.

A portable gamma camera based on the multianode technology has been built and tested. The camera consists in optically coupling four “Flat Panel” H8500 PSPMTs to a 100×100×4 mm 3 CsI(Na) continuous scintillation crystal. The dimensions of the camera are 17×12×12 cm 3 including the pinhole collimator and it weighs a total of 2 kg. Its average spatial resolution is 2 mm, its energy resolution is about 15%, and it shows a field of view of 95 mm. Because of its portability, its FOV and its cost, it is a convenient choice for osteological, renal, mammary, and endocrine (thyroid, parathyroid and suprarenal) scintigraphies, as well as other important applications such as intraoperatory detection of lymph nodes and surgical oncology. We describe the simulations performed which explain the crystal choice, the mechanical design of the camera and the method of calibration and algorithms used for position, energy and uniformity correction. We present images taken from phantoms. We plan to increase the camera sensitivity by using a four-holes collimator in combination with the MLEM algorithm, in order to decrease the exploration time and to reduce the dose given to the patient.

Silicon sensor technologies with reduced dead area at the sensor's perimeter are under development at a number of institutes. Several fabrication methods for sensors which are sensitive close to the physical edge of the device are under investigation utilising techniques such as active-edges, passivated edges and current-terminating rings. Such technologies offer the goal of a seamlessly tiled detection surface with minimum dead space between the individual modules. In order to quantify the performance of different geometries and different bulk and implant types, characterisation of several sensors fabricated using active-edge technology were performed at the B16 beam line of the Diamond Light Source. The sensors were fabricated by VTT and bump-bonded to Timepix ROICs. They were 100 and 200 μ m thick sensors, with the last pixel-to-edge distance of either 50 or 100 μ m. The sensors were fabricated as either n-on-n or n-on-p type devices. Using 15 keV monochromatic X-rays with a beam spot of 2.5 μ m, the performance at the outer edge and corners pixels of the sensors was evaluated at three bias voltages. The results indicate a significant change in the charge collection properties between the edge and 5th (up to 275 μ m) from edge pixel for the 200 μ m thick n-on-n sensor. The edge pixel performance of the 100 μ m thick n-on-p sensors is affected only for the last two pixels (up to 110 μ m) subject to biasing conditions. Imaging characteristics of all sensor types investigated are stable over time and the non-uniformities can be minimised by flat-field corrections. The results from the synchrotron tests combined with lab measurements are presented along with an explanation of the observed effects.

Hybrid pixel detectors like the Medipix and TIMEPIX developed by the Medipix collaboration combined with high-z materials are of growing interest. In particular the TIMEPIX detector can be operated in photon counting mode and time-over-threshold mode (ToT) to obtain spectral information. Previous studies showed that 110 μm pixel sizes obtain a better energy resolution than 55 μm pixel sizes. Furthermore, threshold scans obtained a better spectral resolution than operation in ToT mode. In this work the influence of noise sources in different measurement approaches on the spectral response of a TIMEPIX chip bump-bonded to CdTe sensor are presented. Two 1mm thick CdTe sensors with pixel sizes of 55 μm and 110 μm, bump-bonded to a TIMEPIX readout chip, were evaluated at the Diamond Light Source synchrotron. A finely collimated, perpendicular pencil beam with x-ray energies of 25 keV and 79 keV was used to investigate single pixels. A small area of 10x10 pixels was investigated in ToT-mode and compared to a threshold scan of the same pixels on both detectors. The measurements are compared to an analytical SPICE/Python simulation that emulates photon counting and time-over-threshold mode.

Reduced edge or "edgeless" detector design offers seamless tileability of sensors for a wide range of applications from particle physics to synchrotron and free election laser (FEL) facilities and medical imaging. Combined with through-silicon-via (TSV) technology, this would allow reduced material trackers for particle physics and an increase in the active area for synchrotron and FEL pixel detector systems. In order to quantify the performance of different edgeless fabrication methods, 2 edgeless detectors were characterized at the Diamond Light Source using an 11 μm FWHM 15 keV micro-focused X-ray beam. The devices under test were: a 150 μm thick silicon active edge pixel sensor fabricated at VTT and bump-bonded to a Medipix2 ROIC; and a 300 μm thick silicon strip sensor fabricated at CIS with edge reduction performed by SCIPP and the NRL and wire bonded to an ALiBaVa readout system. Sub-pixel resolution of the 55 μm active edge pixels was achieved. Further scans showed no drop in charge collection recorded between the centre and edge pixels, with a maximum deviation of 5% in charge collection between scanned edge pixels. Scans across the cleaved and standard guard ring edges of the strip detector also show no reduction in charge collection. These results indicate techniques such as the scribe, cleave and passivate (SCP) and active edge processes offer real potential for reduced edge, tiled sensors for imaging detection applications.

High quantum efficiency is important in X-ray imaging applications. This means using high-Z sensor materials. Unfortunately many of these materials suffer from defects that cause non-ideal charge transport. In order to increase the understanding of these defects, we have mapped the 3D response of a number of defects in two 1 mm thick CdTe sensors with different pixel sizes (55μm and 110 μm) using a monoenergetic microbeam at 79 keV. The sensors were bump bonded to Timepix read out chips. Data was collected in photon counting as well as time-over-threshold mode. The time-over-threshold mode is a very powerful tool to investigate charge transport properties and fluorescence in pixellated detectors since the signal from the charge that each photon deposits in each pixel can be analyzed. Results show distorted electrical field around the defects and indications of excess leakage current and large differences in behavior between electron collection and hole collection mode. The experiments were carried out in the Extreme Conditions Beamline I15 at Diamond Light Source.

A three million pixels photon counting area detector for the coherent diffraction imaging beam line (113) of Diamond Light Source has been developed by a joint team of Diamond and STFC staff. The detector is the state of the art of X-ray detection technology since it exploits the latest generation of Medipix ASICs family that introduced a number of innovations. The specifications required by the beam line represented a severe challenge to all of the components of the detector. The frame rate of Excalibur is up to 1,000 frames per second when stored in local RAM or up to 100 frames per second when streamed to storage. Tests with an X-ray set show the imaging capabilities of the detector as well as the data acquisition speed.

High stopping power is one of the most important figures of merit for X-ray detectors. CdTe is a promising material but suffers from: material defects, non-ideal charge transport and long range X-ray fluorescence. Those factors reduce the image quality and deteriorate spectral information. In this project we used a monochromatic pencil beam collimated through a 20μm pinhole to measure the detector spectral response in dependance on the depth of interaction. The sensor was a 1mm thick CdTe detector with a pixel pitch of 110μm, bump bonded to a Timepix readout chip operating in Time-Over-Threshold mode. The measurements were carried out at the Extreme Conditions beamline I15 of the Diamond Light Source. The beam was entering the sensor at an angle of \texttildelow20 degrees to the surface and then passed through \texttildelow25 pixels before leaving through the bottom of the sensor. The photon energy was tuned to 77keV giving a variation in the beam intensity of about three orders of magnitude along the beam path. Spectra in Time-over-Threshold (ToT) mode were recorded showing each individual interaction. The bias voltage was varied between -30V and -300V to investigate how the electric field affected the spectral information. For this setup it is worth noticing the large impact of fluorescence. At -300V the photo peak and escape peak are of similar height. For high bias voltages the spectra remains clear throughout the whole depth but for lower voltages as -50V, only the bottom part of the sensor carries spectral information. This is an effect of the low hole mobility and the longer range the electrons have to travel in a low field.

In this work the results on imaging and spectroscopic performances of 14 × 14 × 1 mm CdTe detectors with 55 × 55 μm and 110 × 110 μm pixel pitch bump-bonded to a Timepix chip are presented. The performance of the 110 × 110 μm pixel detector was evaluated at the extreme conditions beam line I15 of the Diamond Light Source. The energy of X-rays was set between 25 and 77 keV. The beam was collimated through the edge slits to 20 μm FWHM incident in the middle of the pixel. The detector was operated in the time-over-threshold mode, allowing direct energy measurement. Energy in the neighbouring pixels was summed for spectra reconstruction. Energy resolution at 77 keV was found to be ΔE/E = 3.9%.\ud \ud Comparative imaging and energy resolution studies were carried out between two pixel size detectors with a fluorescence target X-ray tube and radioactive sources. The 110 × 110 μm pixel detector exhibited systematically better energy resolution in comparison to 55 × 55 μm. An imaging performance of 55 × 55 μm pixellated CdTe detector was assessed using the Modulation Transfer Function (MTF) technique and compared to the larger pixel. A considerable degradation in MTF was observed for bias voltages below -300 V. Significant room for improvement of the detector performance was identified both for imaging and spectroscopy and is discussed.

Medipix3 is the latest generation of photon counting readout chips of the Medipix family. With the same dimensions as Medipix2 (256 x 256 pixels of 55 mu m x 55 mu m pitch each), Medipix3 is however implemented in an 8-layer metallization 0.13 mu m CMOS technology which leads to an increase in the functionality associated with each pixel over Medipix2. One of the new operational modes implemented in the front-end architecture is the Charge Summing Mode (CSM). This mode consists of a charge reconstruction and hit allocation algorithm which eliminates event-by-event the low energy counts produced by charge-shared events between adjacent pixels. The present work focuses on the study of the CSM mode and compares it to the Single Pixel Mode (SPM) which is the conventional readout method for these kind of detectors and it is also implemented in Medipix3. Tests of a Medipix3 chip bump-bonded to a 300 mu m thick silicon photodiode sensor were performed at the Diamond Light Source synchrotron to evaluate the performance of the new Medipix chip. Studies showed that when Medipix3 is operated in CSM mode, it generates a single count per detected event and consequently the charge sharing effect between adjacent pixels is eliminated. However in CSM mode, it was also observed that an incorrect allocation of X-rays counts in the pixels occurred due to an unexpectedly high pixel-to-pixel threshold variation. The present experiment helped to better understand the CSM operating mode and to redesign the Medipix3 to overcome this pixel-to-pixel mismatch.

Three-dimensional (3D) silicon sensors offer potential advantages over standard planar sensors for radiation hardness in future high energy physics experiments and reduced charge-sharing for X-ray applications, but may introduce inefficiencies due to the columnar electrodes. These inefficiencies are probed by studying variations in response across a unit pixel cell in a 55μm pitch double-sided 3D pixel sensor bump bonded to TimePix and Medipix2 readout ASICs. Two complementary characterisation techniques are discussed: the first uses a custom built telescope and a 120GeV pion beam from the Super Proton Synchrotron (SPS) at CERN; the second employs a novel technique to illuminate the sensor with a micro-focused synchrotron X-ray beam at the Diamond Light Source, UK. For a pion beam incident perpendicular to the sensor plane an overall pixel efficiency of 93.0±0.5% is measured. After a 10o rotation of the device the effect of the columnar region becomes negligible and the overall efficiency rises to 99.8±0.5%. The double-sided 3D sensor shows significantly reduced charge sharing to neighbouring pixels compared to the planar device. The charge sharing results obtained from the X-ray beam study of the 3D sensor are shown to agree with a simple simulation in which charge diffusion is neglected. The devices tested are found to be compatible with having a region in which no charge is collected centred on the electrode columns and of radius 7.6±0.6μm. Charge collection above and below the columnar electrodes in the double-sided 3D sensor is observed. © 2011 IOP Publishing Ltd and SISSA.

X-ray photon-counting detectors consisting of a silicon pixel array sensor bump-bonded to a CMOS electronic readout chip offer several advantages over traditional X-ray detection technologies used for synchrotron applications. They offer high frame rate, dynamic range, count rate capability and signal-to-noise ratio. A survey of the requirements for future synchrotron detectors carried out at the Diamond Light Source synchrotron highlighted the needs for detectors with a pixel size of the order of 50 mu m. Reducing the pixel size leads to an increase of charge-sharing events between adjacent pixels and, therefore, to a degradation of the energy resolution and image quality of the detector. This effect was observed with MEDIPIX2, a photon-counting readout chip with a pixel size of 55 mu m. The lastest generation of the MEDIPIX family, MEDIPIX3, is designed to overcome this charge-sharing effect in an implemented readout operating mode referred to as Charge Summing Mode. MEDIPIX3 has the same pixel size as MEDIPIX2, but it is implemented in an 8-metal 0.13 mu m CMOS technology which enables increased functionality per pixel. The present work focuses on the study of the charge-sharing effect when the MEDIPIX3 is operated in Charge Summing Mode compared to the conventional readout mode, referred to as Single Pixel Mode. Tests of a standard silicon photodiode array bump-bonded to MEDIPIX3 were performed in beamline B16 at the Diamond Light Source synchrotron. A monochromatic micro-focused beam of 2.9 mu m x 2.2 mu m size at 15keV was used to scan a cluster of nine pixels in order to study the charge collection and X-ray count allocation process for each readout mode, Single Pixel Mode and Charge Summing Mode. The study showed that charge-shared events were eliminated when Medipix3 was operated in Charge Summing Mode.

Synchrotron applications such as coherent X-ray diffraction and X-ray photon-correlation spectroscopy require detectors with a pixel pitch of 50 μm as highlighted by a survey with beamline scientists of Diamond Light Source synchrotron. Furthermore, the detector should also have a high frame rate, large dynamic range and large detection efficiency. The Medipix3 readout chip with a pixel pitch of 55 μm emerged as a good candidate to develop a new detector for the aforementioned applications. Additionally, it implements a new operating mode, referred to as Charge Summing Mode (CSM), with the purpose of eliminating charge-shared events. This mode can be very useful in this case, since the charge-sharing effect increases as the detector pixel size decreases. Also, its design is expected to be more radiation hard that its predecessor Medipix2. The present work focuses on the evaluation of the radiation hardness and the CSM operating mode of a Medipix3-based detector in order to develop a large area detector for synchrotron applications.

In this article we report on the use micro-focus synchrotron X-ray radiation and pion beams to compare the detection efficiencies and charge sharing properties of novel 3D detectors to that of the current planar technology. Detector substrates are bump-bonded to the Medipx2 and Timepix chips. 55μm square pixel maps of the detection efficiencies have been produced using X-ray and MIP beams. For X-rays, a drop of 3-4% detection efficiency over the pixel area was found due to the central electrode. The corner electrodes show no degradation in efficiency compared to that of the planar device. For MIPs a drop of 0.5% in efficiency due to the central electrode was observed. Evidence of a considerable reduction in charge sharing in the 3D detectors compared to the planar devices is also shown. ©2009 IEEE.

This study focuses on Monte-Carlo (MC) based techniques to calculate the system matrix (SM) for iterative image reconstruction of small animal PET data. Our goal is to determine in advance if some simplifications can be done to accelerate the MC simulation without jeopardizing the accuracy of the system model. For most PET scanners, the calculation of the SM would imply extremely long simulation times, even when considering symmetries. Our small animal scanner prototype consists of a continuous LSO crystal (42 times 42 times 10 mm3 ) attached to a flat panel position sensitive photomultiplier tube which was simulated using GATE. To compute the SM elements, we investigated three different radioactivity distribution models: (a) homogeneous distribution within the voxel, (b) one unique emission point at the center of the voxel and (c) eight point sources distributed within the voxel. Each of these models was simulated for five representative voxel positions inside the field of view (FOV), two of these voxels in the inner region of the FOV and the other three voxels were in the peripheral region of the FOV. The storage and discretization of the SM elements was performed by means of: (i) tube-of-response (TOR) histograms and (ii) sinograms. By comparing the SM's elements generated for each distribution model at each voxel's position, the accuracy of the models was studied. The results show that in the inner region of the FOV, model C distribution yields the best trade-off between simulation time and SM accuracy. Whereas, for the peripheral region of the FOV, model B yields the best compromise. These results are independent of the discretization process considered. Since the scanner is capable to yield depth-of-interaction (DOI) information, the study was performed taking DOI into account

A simulation toolkit developed for use at Diamond Light Source is presented, accompanied with experimental validation using a silicon pixel-array sensor coupled to a Medipix3RX chip controlled via the Merlin Readout System. The simulation makes use of Geant4, where photons are tracked in order to determine their position of interaction and energy deposition. Further to this, a Finite Element Methods package, Comsol, is used to model the Charge Induction Efficiencies of various sensors. Results are coupled to Geant4 simulations to provide an accurate method for computing the signals generated on each pixel within the sensor and then an algorithm to model the front-end electronics of the device. The validity of the simulation toolkit is tested by investigating charge-sharing effects using a Medipix3RX chip bump-bonded to a silicon pixel-array sensor. The dependence of the imaging parameters, on the energy threshold, is presented from both simulation and experiment for the Medipix3RX chip operated with and without the charge sharing compensation circuitry enabled. This simulation toolkit can be used to calculate image quality parameters for the next generation of detectors, including CdTe, as well as to improve data corrections on existing detectors on synchrotron beamlines.

Coherent X-ray diffraction experiments on synchrotron X-ray beamlines require detectors with high spatial resolution and large detection area. The read-out chip developed by the MEDIPIX3 collaboration offers a small pixel size of 55 microns resulting in a very high spatial resolution when coupled to a direct X-ray conversion segmented silicon sensor. MEDIPIX3 assemblies present also the advantages of hybrid pixel detectors working in single photon counting mode: noiseless imaging, large dynamic range, extremely high frame rate. The EXCALIBUR detector is under development for the X-ray Coherence and Imaging Beamline I13 of the Diamond Light Source. This new detector consists of three modules, each with 16 MEDIPIX3 chips which can be read-out at 100 frames per second in continuous mode or 1000 frames per second in burst mode. In each module, the sensor is a large single silicon die covering 2 rows of 8 individual MEDIPIX3 read-out chips and provides a continuous active detection region within a module. Each module includes 1 million solder bumps connecting the 55 microns pixels of the silicon sensor to the 55 microns pixels of the 16 MEDIPIX3 read-out chips. The detection area of the 3-module EXCALIBUR detector is 115 mm × 100 mm with a small 6.8 mm wide inactive region between modules. Each detector module is connected to 2 FPGA read-out boards via a flexi-rigid circuit to allow a fully parallel read-out of the 16 MEDIPIX3 chips. The 6 FPGA read-out boards used in the EXCALIBUR detector are interfaced to 6 computing nodes via 10Gbit/s fibre-optic links to maintain the very high frame-rate capability. The standard suite of EPICS control software is used to operate the detector and to integrate it with the Diamond Light Source beamline software environment. This article describes the design, fabrication and characterisation of the MEDIPIX3-based modules composing the EXCALIBUR detector.

This contribution reports on the development of a new high rate readout system for the Medipix3 hybrid pixel ASIC developed by the Detector Group at Diamond Light Source. It details the current functionality of the system and initial results from tests on Diamond's B16 beamline. The Merlin system is based on a National Instruments PXI/FlexRIO system running a Xilinx Virtex5 FPGA. It is capable of recording Medipix3 256 by 256 by 12 bit data frames at over 1 kHz in bursts of 1200 frames and running at over 100 Hz continuously to disk or over a TCP/IP link. It is compatible with the standard Medipix3 single chipboards developed at CERN and is capable of driving them over cable lengths of up to 10 m depending on the data rate required. In addition to a standalone graphical interface, a system of remote TCP/IP control and data transfer has been developed to allow easy integration with third party control systems and scripting languages. Two Merlin systems are being deployed on the B16 and I16 beamlines at Diamond and the system has been integrated with the EPICS/GDA control systems used. Results from trigger synchronisation, fast burst and high rate tests made on B16 in March are reported and demonstrate an encouraging reliability and timing accuracy. In addition to normal high resolution imaging applications of Medipix3, the results indicate the system could profitably be used in `pump and probe' style experiments, where a very accurate, high frame rate is especially beneficial. In addition to these two systems, Merlin is being used by the Detector Group to test the Excalibur 16 chip hybrid modules, and by the LHCb VELO Pixel Upgrade group in their forthcoming testbeams. Additionally the contribution looks forward to further developments and improvements in the system, including full rate quad chip readout capability, multi-FPGA support, long distance optical communication and further functionality enhancements built on the capabilities of the Medipix3 chips.

Hybrid silicon photon-counting detectors are becoming standard equipment for many synchrotron applications. The latest in the Medipix family of read-out chips designed as part of the Medipix Collaboration at CERN is the Medipix3, which while maintaining the same pixel size as its predecessor, offers increased functionality and operating modes. The active area of the Medipix3 chip is approx 14mm × 14mm (containing 256 × 256 pixels) which is not large enough for many detector applications, this results in the need to tile many sensors and chips. As a first step on the road to develop such a detector, it was decided to build a prototype single chip readout system to gain the necessary experience in operating a Medipix3 chip. To provide a flexible learning and development tool it was decided to build an interface based on the recently released FlexRIOTM system from National Instruments and to use the LabVIEWTM graphical programming environment. This system and the achieved performance are described in this paper.

Hybrid pixel detectors consisting of an array of silicon photodiodes bump-bonded to CMOS read-out chips provide high signal-to-noise ratio and high dynamic range compared to CCD-based detectors and Image Plates. These detector features are important for SAXS experiments where a wide range of intensities are present in the images. For time resolved SAXS experiments, high frame rates are compulsory. The latest CMOS read-out chip developed by the MEDIPIX collaboration provides high frame rate and continuous acquisition mode. A read-out system for an array of MEDIPIX3 sensors is under development at Diamond Light Source. This system will support a full resolution frame rate of 1 kHz at a pixel counter depth of 12-bit and a frame rate of 30 kHz at a counter depth of 1 bit. Details concerning system design and MEDIPIX sensors characterization are presented.

Digital trigger algorithms performed over large sequences of data can be an efficient way to shift processing time from baseline samples or singles to coincident photo multiplier tube pulses. This paper describes a coincidence processing system intended to implement fully digital trigger and pre-processing algorithms for a positron emission tomography scanner dedicated to breast imaging. In order to efficiently address all the emerging issues of high resolution PET detectors, a high performance DSP processor has been embedded into the backbone of the system. Signals from 12 channels of a dual-head PET camera are acquired in free-running sampling while a first stage of FIFO memories, implemented using a Virtex-II Pro FPGA, translate data from a sequential sample-by-sample processing basis to a more efficient block-by-block one. This approach enables us to carry out trigger and pre-processing tasks in parallel. Moreover, the scheme offers additional benefits: intrinsic temporal coherence, zero data acquisition dead time, and a more flexible software approach to pre- and post-processing issues (from pile-ups and scatter correction to pre-reconstruction processing). It also heavily reduces the bandwidth required for the link to the host computer, enabling the use of a high speed USB port. The DAQ system is capable of handling count rates up to 10 Mevents/s, pre-processing the samples on the fly and lastly delivering data to the host computer for image reconstruction.

A design for an inexpensive depth of interaction (DOI) detector for gamma rays, suitable for nuclear medical applications, especially positron emission tomography (PET), has been developed, studied by simulations and tested experimentally. The detector consists of a continuous LSO-scintillator of dimensions 42/spl times/42/spl times/10 mm/sup 3/ and a new compact large-area (49/spl times/49 mm/sup 2/) position sensitive photo-multiplier (PSPMT) H8500 from Hamamatsu. Since a continuous crystal is used, the scintillation light distribution is not destroyed and its first 3 moments can be used to determine the energy (0th moment), the centroids along the x- and y-direction (1st moments) and the depth of interaction (DOI), which is strongly correlated to the distribution's width and thus its standard deviation (2nd moment). The simultaneous computation of these moments allows a three-dimensional reconstruction of the position of interaction of the /spl gamma/-rays within the scintillating crystal and will be realized by a modified position sensitive proportional (PSP) resistor network. No additional photo detectors or scintillating crystals are needed. According to previous Monte Carlo simulations which estimated the influence of Compton scattering for 511 keV /spl gamma/-rays, the transport of the scintillation light within the detector assembly and also the behavior of the modified PSP resistor network, we expect a spatial resolution of /spl lsim/ 2 mm and a DOI resolution of /spl ap/ 5 mm. The first experimental results presented here yield an intrinsic spatial resolution of /spl lsim/ 1.8 mm and 2.6 mm for the x- and y-direction respectively and a DOI resolution /spl lsim/ 1 cm. Further we measured an energy resolution of 12%-18%.

We have built a PET camera for small animals based on continuous block LSO crystals coupled to a PS-PMT flat panel. When working with continuous crystals, surface treatment is an important factor that strongly determines the main characteristics of the detector module. As a part of the work done for the development of our small animals PET camera, we have investigated the effect of the scintillator crystal surface treatment on the PET detector module performances, in order to optimize crystal configuration. We present the results for spatial resolution, image compression and energy resolution obtained when using different surface treatments in continuous LSO crystals. These results are compared with those obtained from simulations that have been carried out using DETECT2000 package.