Cyril Ponchut

MAXIPIX, a fast readout photon-counting X-ray area detector for synchrotron applications

A 2D photon-counting X-ray detector system with 1.4 kHz frame rate and 55 μm spatial resolution has been developed and commissionned on ESRF beamlines. The system called MAXIPIX (Multichip Area X-ray detector based on a photon-counting PIXel array) consists of a detector module implementing up to five MEDIPIX-2 or TIMEPIX photon-counting readout chips, a custom readout interface board and a Linux acquisition workstation. The detector module readout time is 290 microseconds, allowing the system to achieve sustained frame rates of 280 Hz to 1400 Hz depending on the number of connected chips. An effective time resolution of 60 ns was measured using the ESRF pulsed modes and a TIMEPIX module. The system architecture and characteristics are presented, as well as a summary of its applications on ESRF beamlines.

Improving the performance of high-resolution X-ray spectrometers with position-sensitive pixel detectors

A dispersion-compensation method to remove the cube-size effect from the resolution function of diced analyzer crystals using a position-sensitive two-dimensional pixel detector is presented. For demonstration, a resolution of 23 meV was achieved with a spectrometer based on a 1 m Rowland circle and a diced Si(555) analyzer crystal in a near-backscattering geometry, with a Bragg angle of 88.5 degrees . In this geometry the spectrometer equipped with a traditional position-insensitive detector provides a resolution of 190 meV. The dispersion-compensation method thus allows a substantial increase in the resolving power without any loss of signal intensity.

Fast processes in liquid metal foams investigated by high-speed synchrotron x-ray microradioscopy

Rupture of an individual film in an evolving liquid metal foam is investigated by means of high-speed x-ray radioscopy using white synchrotron radiation. At a frame rate of 5000frames∕s, the rupture event is spread over three to four images. The images show that the remnants of the rupturing film are pulled into the surrounding plateau borders in 600±100μs which conforms well with a liquid movement governed by inertia and not by viscosity. Within one order of magnitude, the viscosity of the liquid involved must be similar to the viscosity of pure liquid aluminium.

Evaluation of a photon-counting hybrid pixel detector array with a synchrotron X-ray source

A photon-counting hybrid pixel detector (Medipix-1) has been characterized using a synchrotron X-ray source. The detector consists of a readout ASIC with 64 � 64 independent photon-counting cells of 170 � 170mm 2 pitch, bumpbonded to a 300mm thick silicon sensor, read out by a PCIbus-based electronics, and a graphical user interface (GUI) software. The intensity and the energy tunability of the X-ray source allows characterization of the detector in the time, space, and energy domains. The system can be read out on external trigger at a frame rate of 100 Hz with 3 ms exposure time per frame. The detector response is tested up to more than 7 � 10 5 detected events/pixel/s. The point-spread response shows o2% crosstalk between neighboring pixels. Fine scanning of the detector surface with a 10mm beam reveals no loss in sensitivity between adjacent pixels as could result from charge sharing in the silicon sensor. Photons down to 6 keV can be detected after equalization of the thresholds of individual pixels. The obtained results demonstrate the advantages of photon-counting hybrid pixel detectors and particularly of the Medipix-1 chip for a wide range of X-ray imaging applications, including those using synchrotron X-ray beams. r 2001 Published by Elsevier Science B.V.

Characterization of X-ray area detectors for synchrotron beamlines

In order to deal with the problem of quantitative and consistent evaluation of two-dimensional X-ray detectors at synchrotron beamlines, the methodology for X-ray area detector characterization is reviewed. It is based on the definition of a minimum yet complete set of imaging parameters able to describe any kind of two-dimensional detector regardless of its operating range, field of application and detecting principle. Measuring and derivation methods are reviewed for each parameter. Imaging parameters are to a large extent directly exploitable to assess the performance of a detector for any scientific application. Imaging characterization aims at helping two-dimensional detector developers and two-dimensional detector users in defining or choosing the device best suited for a given application, based on quantitative arguments.

Two-dimensional camera for millisecond range time-resolved small-and wide-angle X-ray scattering

A combined small-angle and wide-angle X-ray scattering (SAXS/WAXS) camera has been implemented using area detectors suitable for real time experiments down to millisecond time range. The design is based on the existing high brilliance SAXS camera with a sample-to-detector distance variable from 1 m to 10 m and to which a two-dimensional WAXS detector is coupled. Two independent image intensified CCD detectors allow simultaneous real-time SAXS/WAXS experiments on oriented samples down to the millisecond time range. A wide scattering vector range spanning from 0.001 A-1 to 6 A-1 is covered by this combined setup. Both detectors have single photon sensitivity and the spatial resolution is about 200 m. The WAXS detector is mounted at an angle inclined to the primary beam and the process of image transformation into non-arbitrary scattering vector coordinates is demonstrated for a standard p-bromobenzoic acid sample.

XAS and XMCD under high magnetic field and low temperature on the energy-dispersive beamline of the ESRF

The present paper demonstrates the feasibility of X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) under high magnetic fields up to 26 T and low temperatures down to 5 K on the ID24 energy-dispersive XAS beamline of the ESRF. The pulsed magnetic field set-up, entirely developed at the ESRF, is described as well as the beamline set-up, the synchronization and the measurement procedure. It allows field strengths up to 30 T. Finally, as an example, we report a recent XMCD study at the Re L2 and L3 absorption edges of the double perovskite Sr2CrReO(6).

A new detector for sub-millisecond EXAFS spectroscopy at the European Synchrotron Radiation Facility

The design and performance of the new sub-millisecond detector for time-resolved X-ray absorption spectroscopy at ID24 at the ESRF is described.

A large-solid-angle X-ray Raman scattering spectrometer at ID20 of the European Synchrotron Radiation Facility

An end-station for X-ray Raman scattering spectroscopy at beamline ID20 of the European Synchrotron Radiation Facility is described. This end-station is dedicated to the study of shallow core electronic excitations using non-resonant inelastic X-ray scattering. The spectrometer has 72 spherically bent analyzer crystals arranged in six modular groups of 12 analyzer crystals each for a combined maximum flexibility and large solid angle of detection. Each of the six analyzer modules houses one pixelated area detector allowing for X-ray Raman scattering based imaging and efficient separation of the desired signal from the sample and spurious scattering from the often used complicated sample environments. This new end-station provides an unprecedented instrument for X-ray Raman scattering, which is a spectroscopic tool of great interest for the study of low-energy X-ray absorption spectra in materials under in situ conditions, such as in operando batteries and fuel cells, in situ catalytic reactions, and extreme pressure and temperature conditions.

Studying macromolecular solutions without wall effects by stroboscopic small-angle x-ray scattering

Small-angle x-ray scattering patterns have been collected stroboscopically from ballistic microdrops of cytochrome C protein solution. The microdrops, measuring around 80 μm diameter (∼268pl), were generated by a drop-on-demand system and traveled at approximately 1.7 m/s through a 3 μm synchrotron radiation beam. The scattering patterns were accumulated on a pixel detector, which was activated for a few microseconds during the transit time of each microdrop through the microbeam. The stability of the microdrop sequence allowed observing interface scattering from HCl buffer microdrops. The small-angle x-ray scattering data provide information on the protein conformation free of physical boundaries.